12
Starter Relay
Comments:
For Smart Start system.
13
EVAP (evaporative emission) purge valve
System Operation
The engine is controlled by the PCM. Information from the various sensors, encoders and switches is brought together in the PCM. The PCM also receives information from other control modules via the CAN databus. All the information is processed in the PCM and is used to control or regulate the different actuators.
These are the throttle control unit, the injectors, the camshaft adjuster and the ignition coil. Some values are sent via the CAN databus to other systems.
Overview
The following functions are regulated or controlled by the PCM:
- Starting process
- Fuel supply to the engine including lambda control
- Ignition timing including knock control
- Idle speed control
- Valve timing via the camshaft adjuster for intake and exhaust camshafts including internal exhaust gas recirculation
- A/C compressor
- EVAP purge valve
Fuel is supplied to the engine via a sequential multi-point injection system. Ignition is provided by a distributorless ignition system with one ignition coil unit supplying ignition voltage to all cylinders. Ignition is controlled for each cylinder individually.
Starting process
The PCM enables the starting process when a key providing a valid code is read via the PATS. This code is then verified in the GEM and compared with the saved code. If this code is recognized as correct, matching with other modules is carried out. Only if this matching was successful is starting enabled in the PCM. The PCM connects earth to the starter relay, which then connects power to the starter solenoid. As soon as the engine reaches a certain speed, the PCM disconnects the starter relay and so turns off the starter. This protects the starter.
If the engine does not turn or turns only slowly, the starting process is aborted by the PCM.
Calculation of valve timing adjustment angle
The 1.6L Duratec-16V Ti-VCT (Sigma) engine features two mutually independent camshaft adjustment units.
This allows the PCM to continuously adjust the intake and exhaust-side camshaft adjustments independently of one another. The timings are adjusted by the PCM on the basis of a calibration that is primarily dependent on the engine load and engine speed.
The advantages of this system are:
- Higher torque and improved torque characteristics
- Lower fuel consumption
- Optimized emission behaviour
The continuous adjustment of the camshafts by the PCM is guaranteed by the VVT solenoids, the camshaft adjustment units and two CMP sensors. The adjustment range of the cam adjuster, which works according to the vane cell principle, is 52° crank angle for the intake camshaft and 47° crank angle for the exhaust camshaft. On starting the engine, both camshafts are mechanically locked in their starting positions. The intake camshaft is in the maximum late position and the exhaust camshaft in the maximum early position.
Control is divided into four main areas:
- Low engine speed and low load
- Partial load
- Low engine speed and high load
- High engine speed and high load
At low engine speed and low load, the exhaust valves open early and the intake valves open late. The result is lower consumption and smoother idle running.
In the partial load range, the exhaust valves and the intake valves open late. The late opening of the exhaust valves results in a good utilization of the expanding gases in the cylinder. Closing the exhaust valves after Top Dead Centre allows internal EGR (exhaust gas recirculation) through aspiration of exhaust gases into the combustion chamber. Moreover, the intake valves close after Bottom Dead Centre, allowing the fresh air/fuel mixture and exhaust gases to flow back into the intake tract. This results in lower consumption and less pollutant emission.
At low engine speed and high engine load, the exhaust valves open late and the intake valves open early. Due to the resulting valve opening overlap at Top Dead Centre, the pulsating gas column within the combustion chamber is utilized to achieve better charging of the combustion chamber. The result is increased torque at lower RPM.
At high engine speeds and high engine load, the exhaust valves open early and the intake valves close late. Because a rapid gas exchange must be achieved at high engine speeds, the early opening of the exhaust valves achieves better expulsion of the exhaust gas and the late closing of the intake valves improves cylinder charge efficiency. Optimum power output is achieved.
Fuel metering
With “ignition on, engine off”, the fuel pump runs for one second to build up the system pressure and is then deactivated for safety reasons.
The fuel metering is determined via open or closed-loop control.
The open control loop differs from the closed control loop in that the lambda control is deactivated.
The PCM switches back from closed to open-loop control when the HO2S cools down or fails, as well as during during acceleration, coasting and Wide Open Throttle operation.
The calculation of fuel metering by the PCM depends on the operating state and comprises:
- Control of the fuel pump
- Calculation of the fuel quantity during starting (cranking) of the engine
- Calculation of the desired air/fuel ratio
- Air mass calculation
- Calculation of fuel quantity for the different operating states and corresponding fuel adjustment measures.
Open loop control
Open loop control is used primarily for fuel injection, as long as the signals of the HO2S are not involved in the calculation of the PCM.
The two most important reasons that make it absolutely essential to run the engine without lambda control (open-loop control) are the following operating conditions:
- Cold engine (starting, warm-up phase)
- Full-load operation (WOT (wide open throttle))
Under these operating conditions the engine needs a rich air/fuel mixture with lambda values below λ = 1 in order to achieve optimum running or optimum performance.
Closed-loop control
Closed loop control ensures strict control of exhaust emissions in conjunction with the TWC and economical fuel consumption. With closed loop control, the signals from the HO2S are analyzed by the PCM and the engine always runs in the optimum range of λ = 1. In addition to the normal HO2S, the signal from the monitoring sensor for the catalytic converter is also included in the control. The lambda control is optimized on the basis of this data.
Ignition angle calculation
Since propagation of the flame front in the air/fuel mixture always takes the same amount of time, the ignition of the air/fuel mixture has to take place earlier or later depending on the engine speed. The higher the speed, the earlier ignition must occur. This ensures that maximum combustion pressure is achieved immediately after Top Dead Centre.
The following provide the basis for calculating the ignition angle:
- Engine speed
- Engine load.
- Engine coolant temperature
- KS signal
The ignition angle has a major impact on engine operation. It influences:
- engine performance
- exhaust emissions and
- fuel consumption
The higher the engine load, i.e. the torque demand, the richer the air/fuel mixture, the longer the combustion period and the earlier the ignition.
The engine load is determined by the PCM on the basis of the MAF signal and the throttle valve position. The ignition timing is calculated taking both of these variables and the engine speed into account. It is based on ignition maps stored in the PCM. The ignition timing is adjusted according to the operating condition of the engine, for cold starting for example.
Ignition map
The data in the ignition maps is obtained from test series. Particular attention is paid to the emission behaviour, power and fuel consumption of the engine. The ignition map is stored in the data memory of the PCM.
By adjusting the ignition timing it is also possible to influence the engine speed to some extent without having to change the throttle valve position. This has advantages for idling stabilization, as the engine speed and hence the engine torque respond far more quickly to a change in the ignition timing than to a change in the throttle valve position. Furthermore, the ignition timing can be changed much more quickly.
To keep the ignition point as close as possible to the knock limit and so optimize the efficiency of the engine, two KS are installed in the engine, which pick up the mechanical vibrations of the engine and convert them into an electrical signal for the PCM.
1
Pressure characteristics in cylinder
Knocking combustion takes place when flame speeds near the speed of sound occur. This can happen towards the end of combustion in particular, when unburnt gaseous mixture on the combustion chamber walls self-ignites due to the increase in pressure following initiation of regular combustion. The resulting pressure peaks damage the pistons, cylinder head gasket and cylinder head.
If knocking combustion occurs, the ignition point is adjusted in the late direction only for the cylinder concerned, until knocking combustion ceases. The ignition point is then slowly adjusted back in the early direction, until the ignition point specified by the PCM is reached again.
Alternator control (Smart Charge)
4
LIN (local interconnect network) databus
Comments:
Via the
LIN databus, the
PCM receives information about the alternator load, and the alternator receives information about the optimum voltage calculated by the
PCM.
5
Charge warning light in instrument cluster
Comments:
Is controlled by the
PCM via the
CAN databus.
6
Temperature signal from
IAT sensor
The Smart Charging System comprises the following functions:
- Battery temperature calculation and charging voltage control
- Alternator load feed forward function
- Alternator deactivation on starting the engine
- Idle speed increase under low voltage / high electrical load conditions (to increase alternator output and reduce battery discharge)
In the case of a conventional alternator, a fixed voltage value (setpoint value) is specified by the internal voltage regulator and used to control the system voltage. Although the voltage regulator functions of the alternator are retained with the Smart Charge system, the voltage setpoint is calculated in advance by the PCM.
The Smart Charge system runs without any additional components, features a self-test function in the PCM and can be diagnosed using the Integrated Diagnostic System (IDS).
Under high alternator load, the PCM can increase the idling speed above the basic idling speed in steps of up to 150 rpm, to increase the alternator output.
After the engine has started, the alternator generates alternating current (AC) which it converts to direct current (DC) internally. The DC current is supplied to the battery and vehicle electrical consumers at a voltage regulated by the voltage regulator (located on the back of the alternator). The voltage of the charging system is controlled by the PCM. This is temperature-dependent. The battery is more efficiently charged with a higher voltage when the battery is cold and a lower voltage when the battery is warm. The PCM is able to adjust the charging voltage according to the battery temperature. The battery temperature is calculated on the basis of IAT and ECT.
The PCM simultaneously monitors and controls the output voltage of the alternator. When the current consumption is high or the battery is excessively discharged, the system is able to increase the idle speed. To minimize engine drag torque when starting the engine, the PCM deactivates the alternator. After the engine has started, the PCM increases the alternator output until the required value is reached.
The PCM controls the function of the charge warning light, which is located in the instrument cluster. The PCM is therefore responsible for ensuring that the charge warning light goes off after the engine has started and comes on in the event of a fault. The charge warning light is also activated by the PCM when the ignition is on, the engine is off and the engine stalls.
The battery charging current is optimized through continuous calculation of the battery temperature and regulation of the alternator output voltage. The alternator load feed forward function informs the PCM in advance of imminent electrical loads, i.e. before the alternator torque changes. Based on this information, the PCM is able to guarantee greater idling stability.
If the Smart Charge system is faulty, the voltage setpoint is adjusted to a value defined in the alternator. The charge warning light comes on in the event of faults in the system and if the charging voltage is too low.
Component Description
Powertrain Control Module (PCM)
The PCM optimizes engine power and emissions at all times by processing the sensor signals and information received via the CAN databus and using these for open or closed loop control of the different variables.
The PCM contains part of the PATS.
The PCM is supplied with battery power via fuse F10 in the BJB (battery junction box). This power supply is needed to ensure that saved data is not lost when the engine is switched off. After the engine has been switched off, the PCM continues to be supplied with power for a further 10 seconds to allow data from RAM (random access memory) of the PCM to be written to non-volatile memory.
A voltage transformer integrated into the PCM provides various components of the PCM and sensors on the engine with a 5 volt supply. Functions which work at battery voltage, such as the injectors, are controlled via internal power end stages or, like the ignition coil, via an external power end stage in the ignition coil itself.
To guarantee optimum engine running at all times, the PCM has several adaptive (self-learning) functions. These adapt the output signals to changing circumstances, such as wear or system faults.
In some cases a faulty signal is also replaced with a substitute value or limited. A substitute value can be calculated from other signals or it can be predefined by the PCM. The substitute value allows the vehicle to keep on running without the emission values changing unduly. Depending on the signal failure, the PCM operates in emergency mode. In this mode, the engine power and/or the engine speed is reduced to prevent further damage.
Depending on the faulty signal, a fault code is stored in the error memory of the PCM.
The PCM processes signals from different sensors and evaluates these with internal software. The following sensors send signals to the PCM:
- CMP sensors
- CKP sensor
- MAF sensor
- KS
- ECT sensor
- EOP switches
- TP (throttle position) sensor
- APP sensor
- HO2S
- Catalyst monitor sensor
- IAT sensor
- PSP switches
- Air conditioning (A/C) pressure sensor
- Alternator
The following components receive signals from the PCM:
- Powertrain Control Module relay
- A/C clutch relay
- Injectors
- EI ignition coil
- Cooling fan module
- Throttle control unit
- VVT solenoids
- Starter relay
- EVAP purge valve
- Alternator
- HO2S heating element
- Catalyst monitor sensor heating element
The PCM receives the following signals via the CAN databus:
- Outside air temperature
- APP
- CPP
- BPP
- Vehicle speed
- Query for A/C compressor
- PATS
The PCM sends the following signals via the CAN databus:
- Fuel pump relay on/off
- Engine speed
- Warning lamps on/off
- PATS
- ECT
Camshaft position (CMP) sensor
The intake and exhaust camshafts each have a sensor installed on them. The CMP sensors are used by the PCM for cylinder-1-identification and thus to determine the injection sequence. The signal is also needed to regulate the camshaft adjustment.
Based on the calculated camshaft position and information about the crankshaft position, the PCM is able to determine the correct ignition timing and the correct injection timing for each individual cylinder. Also it can accurately identify a cylinder that is showing a tendency to knocking combustion.
The CMP sensor is realized as a Hall effect sensor and is provided by the PCM with a 5 volt supply. The Hall effect sensor emits a signal when the pulse segments incorporated into the sensor wheel rotate past the tip of the sensor. Thanks to the composition of the pulse segments, and combined with the signals from the CKP sensor, the PCM is able to calculate the position of the individual camshafts at any time. If an increase occurs in the area of the sensor, the PCM receives a 'low' signal with a maximum voltage of 0.5V. If a gap occurs in the area of the sensor, a 'high' signal is sent to the PCM. In this case the voltage is approx. 4.5V.
If one or both CMP sensors fail, a fault is saved in the error memory of the PCM and the camshaft adjustment and knock control are deactivated.
Crankshaft position sensor
The CKP sensor is used by the PCM to detect the engine speed and for TDC (top dead center) recognition.
The periphery of the flywheel has 35 indentations on the engine side, one of which is twice as large as the others. This is used for TDC recognition. The CKP sensor works according to the induction principle and generates a sinusoidal signal voltage whose level and frequency are speed-dependent.
From the frequency of the signal the PCM calculates the engine speed. Due to the double gap in the flywheel, with every engine revolution an altered sinusoidal oscillation is generated, with the help of which the PCM recognizes the TDC position of the crankshaft.
The signal from the CKP sensor is used to determine:
- the crankshaft position
- the engine speed
- the ignition timing
- the fuel injection point
- the adjustment angle of the VVT units
1
Zero transitions: Spacing small/amplitude large
2
Zero transitions: Spacing large/amplitude small
The acceleration of the flywheel at each power stroke results in a change in the CKP signal.
During the power stroke, the combustion pressure acting on the piston causes an acceleration of the crankshaft and thus also of the flywheel. This is apparent in the voltage curve from slightly higher frequencies and amplitudes of the CKP signal.
If the CKP signal fails, no substitute function is provided. The engine is switched off or the engine will not start and a fault is stored in the error memory of the PCM.
Knock Sensors (KS)
The knock sensors convert mechanical vibrations of the cylinder block into electrical pulses which can then be processed by the PCM.
The KS consists of piezoceramic crystals which generate a voltage when a mechanical load is applied to them.
When fastening the KS, make sure the specified torque is adhered to. In this way a defined initial tension is applied to the crystals which exerts an influence on the operation of the KS.
When the engine is running, the pressure fluctuations arising due to the combustion process cause vibrations in the cylinder block. These act on the crystals in the KS, causing the sensors to produce an output signal. These signals are evaluated by the PCM and compared with stored data.
1
Pressure characteristics in cylinder
The PCM is able to identify knocking combustion on each individual cylinder. If knocking occurs, the ignition point for the cylinder concerned is adjusted to late for a few crankshaft revolutions, until knocking combustion ceases. After that the ignition point is slowly returned to the calculated value.
If the signal from one or both KS is implausible or absent, knock control is deactivated. The PCM defaults to an ignition map which is further away from the knock limit, so as not to damage the engine. If a fault occurs, a fault code is stored in the error memory of the PCM.
Heated oxygen sensors (HO2S) and catalyst monitor sensors
The HO2S are located upstream of the TWC. The catalyst monitor sensors are downstream of the TWC. The HO2S measures the residual amount of oxygen in the exhaust before the TWC.
The catalyst monitor sensor measures the amount of oxygen in the exhaust after the TWC.
Both the HO2S and the catalyst monitor sensors send this data to the PCM.
HO2S preheating
The heated oxygen sensor is only able to work at temperatures above 300°C. The normal working temperature in the vehicle is between 350°C and 850°C. If the temperature rises above 1000°C, the heated oxygen sensor will be irreparably damaged.
HO2S are installed so that the optimum operating temperature can be reached as quickly as possible. The heating also serves to maintain a suitable operating temperature while coasting, for example, when no hot gases are flowing past the sensor.
The heating element in the HO2S is a PTC (positive temperature coefficient) resistor. The heating element is supplied with battery voltage as soon as the Powertrain Control Module relay engages. The HO2S is earthed via the PCM. As the heating current is high when the element is cold, it is limited via PWM (pulse width modulation) in the PCM until a certain current value is reached. The PCM then permanently connects the heating element to earth.
The PCM is able to detect faults in the heating element and store these in the error memory.
Heated oxygen sensor
The two HO2S are installed before the TWC. The HO2S consists of a solid galvanic zirconium dioxide cell surrounded by a porous ceramic body. The output voltage of the HO2S depends on the amount of oxygen in the exhaust gas and at lambda = 1 lies between 300 and 500 mV. If the air/fuel mixture becomes richer, the voltage rises as high as 900mV. If it becomes leaner, the voltage falls as far as 0V.
The HO2S are used by the PCM to determine the amount of oxygen in the exhaust gas before it enters the TWC. This allows the PCM to regulate the injected volume of fuel so as to provide an optimum air/fuel mixture for combustion of lambda = 1 at all times.
The HO2S emit a linear voltage signal which corresponds to the ratio of oxygen in the exhaust gas to the oxygen in the ambient air. For this comparison, the HO2S has a small bore hole through which the ambient air reaches into the interior.
Catalyst monitor sensor
The two catalyst monitor sensors are arranged downstream of the TWC. They are used by the PCM to measure the amount of oxygen in the exhaust gas after it emerges from the TWC. If all the conditions for catalyst diagnostics are met, based on this information the PCM can check that the TWC is working satisfactorily. The information is also used to improve the air/fuel mixture adjustment.
The catalyst monitor sensors work in a similar way to the HO2S, except that they emit a binary rather than a linear signal to the PCM. This signal changes very markedly if the oxygen content of the exhaust gas changes. For this reason, catalyst monitor sensors are also called "jump lambda sensors".
Variable valve timing (VVT) solenoid
One VVT solenoid is installed for the intake camshaft and one for the exhaust camshaft.
The VVT solenoids are used to regulate the camshaft adjustment units, which in turn adjust the valve timings in the early or late directions. In this way the engine performance is increased and internal exhaust gas recirculation is realized. The VVT solenoids for the intake and exhaust camshafts differ only in terms of the position of the fastening point by which they are fixed to the camshaft adjustment bridge.
Via the VVT solenoid, under the prevailing EOP, a defined quantity of engine oil is allowed into and out of the camshaft adjustment units. In this way the valve timings are adjusted according to the operating condition of the engine.
The VVT solenoids are actuated via a PWM signal by the PCM.
A
Bore hole for connection to chamber A
B
Bore hole for connection to chamber B
3
Engine oil pressure supply bore and ring groove for camshaft adjustment unit chamber B
5
Engine oil pressure supply bore and ring groove for camshaft adjustment unit chamber A
6
Engine oil pressure supply bore for
VVT solenoid
When idling and during deceleration, the VVT solenoids are activated repeatedly by the PCM in order to remove any dirt which may be on the bore holes and ring grooves.
If a fault is detected on the VVT solenoids, they are no longer actuated.
To avoid a malfunction of the VVT units at excessively low ambient or engine-oil temperatures, they are activated by the PCM with a time delay via the VVT solenoids. The PCM obtains the information needed for this purpose from the ECT sensor and the IAT sensor.
Mass Air Flow (MAF) sensor / Intake Air Temperature (IAT) sensor
The MAF sensor works according to the hot-wire principle.
The MAF sensor is powered via the Powertrain Control Module relay in the BJB. The MAF sensor and the IAT sensor are connected to earth via the PCM.
The MAF sensor has an extended moulding which projects into the centre of the outlet pipe of the air filter, where it measures the air mass aspirated by the engine and the intake air temperature.
The air mass aspirated by the engine is determined on the basis of the cooling effect of the intake air via a hot-film element in the MAF sensor. The greater the aspirated air mass, the greater the cooling effect and the lower the electrical resistance of the hot-film element. The electronics in the MAF sensor process this resistance value and send a voltage signal to the PCM corresponding to the aspirated air mass.
This analogue voltage signal is between 0.5V and 5V. With a small aspirated air mass the voltage signal is low, with a large aspirated air mass it is correspondingly high.
From this voltage, the PCM calculates the air mass aspirated by the engine. Using this value, the quantity of fuel to be injected and the ignition timing are determined.
The MAF sensor is monitored by the PCM and in the event of malfunctions corresponding fault codes are saved in the error memory of the PCM. If a fault occurs in the MAF sensor, a substitute value is calculated from the engine speed and the throttle flap position.
The MAF is integrated into the IAT sensor. This is realized as an NTC (negative temperature coefficient) resistor, whose resistance diminishes with decreasing temperature. Via the PCM, a 5V reference voltage is applied to the IAT sensor. The voltage at the IAT drops by a varying amount depending on the resistance. From this voltage drop, the PCM determines the intake air temperature.
If the IAT sensor is faulty, a fixed value of 20°C is used for the calculation.
Accelerator pedal position (APP) sensor
The APP sensor identifies the current position of the accelerator and sends this to the PCM and the GEM.
The APPsensor is a double contactless inductive sensor. The APP sensor is integrated with the accelerator pedal in the accelerator pedal module.
The inductive sensor essentially works in a similar way to a transformer. The incoming DC voltage first has to be converted into AC voltage. Depressing the accelerator pedal moves a rotor. This rotor induces the AC voltage between the primary coil and the secondary coil.
In the APP sensor the signals are split as follows:
- APP 1 = PWM signal to the GEM and from there via the CAN data bus to the PCM.
- APP 2 = the analogue DC (direct current) signal is sent directly to the PCM.
Both signals are monitored by the PCM for plausibility.
If one of the two APP sensors fails then the vehicle drives with reduced acceleration. Top speed can nevertheless be achieved.
If both of the APP sensors fail, the engine is regulated to a defined speed following a plausibility check after the BPP switch and brake light switch have been actuated once. The vehicle can then only be accelerated to a defined speed.
In either case, a fault is saved in the error memory of the PCM.
Clutch pedal position (CPP) switch
The CPP switch sends an earth signal to the GEM as soon as the clutch is depressed. This signal is passed on by the GEM via the CAN databus to the PCM. The PCM needs this signal to improve engine running performance during switching processes.
Failure of the CPP switch can cause the engine to judder during the switching process.
Brake pedal position (BPP) switch
The BPP switch tells the PCM whether the vehicle is being braked. In its rest state the switch is closed and sends an earth signal to the GEM. This signal is sent to the PCM via the CAN databus.
The brake light switch is likewise connected to the GEM and is opened in the rest state. When the vehicle is braked, the brake light switch sends a signal to the GEM. This compares the signals from the BPP switch and the brake light switch. If a discrepancy occurs, a fault is stored in the error memory of the GEM.
Information from both switches is needed for emergency operation if the APP sensor fails.
If the APP sensor fails and the BPP switch is actuated, the engine is set to idle speed via the PCM.
Air Conditioning (A/C) Pressure Sensor
The A/C pressure sensor is installed on the high-pressure side of the A/C (air conditioning). The A/C pressure sensor sends a continuous analogue signal to the PCM, which describes the pressure status in the A/C high pressure line. More accurate fan control is possible thanks to this linear signal profile. The input voltage is 5V, the output voltage is between 0.5V and 4.5V depending on the cryogenic fluid pressure. When the cryogenic fluid pressure is low, the output voltage is also low.
The signal is also used to turn the A/C compressor on or off via the A/C clutch relay at certain pressure values.
Air conditioning clutch relay
The A/C clutch relay is located in the BJB at slot R3.
The A/C clutch relay switches the A/C compressor on and off. It is actuated by the PCM. The driver's wishes are communicated to the PCM from the climate control operating panel via the CAN databus.
If a fault occurs due to the pressure conditions in the A/C circuit, the A/C compressor is turned off via the A/C clutch relay. The PCM also turns off the A/C clutch relay for a short time under certain conditions (high engine load, when accelerating, high coolant temperature).
Throttle control unit
4
Throttle flap return spring
6
Electric motor with pinion
CAUTION:The throttle control unit must not be repaired or adjusted. The stop of the throttle valve must on no account be adjusted.
The APP sensor provides the PCM with information about the driver's request for acceleration.
The throttle control unit receives a corresponding input signal from the PCM. An electric motor then moves the throttle valve shaft by means of a set of gears. The throttle valve position is constantly detected by the TP sensor and information about the position is processed and monitored by the PCM. With the throttle valve position kept constant, the ignition angle and the injected fuel quantity are then varied to meet the torque demands. Depending on the operating state of the engine, a change in the position of the throttle flap may not be necessary when the APP sensor changes.
If a fault develops in the throttle control unit, a standby function is executed. This standby function allows a slight opening of the throttle flap, so that enough air passes through to allow limited engine operation. For this purpose, there is a throttle flap adjustment screw on the throttle housing. The return spring closes the throttle flap until the stop of the toothed segment touches the stop screw. In this way a defined throttle flap gap is formed for limp home mode.
The stop screw has a spring loaded pin, which holds the throttle flap open for limp home mode. In normal operating mode, this spring loaded pin is pushed in by the force of the electric motor when the throttle flap must be closed past the limp home position (e.g. for idle speed control or overrun shutoff).
Engine Oil Pressure (EOP) switch
This connects earth to the EOP depending on the PCM. This signal is needed to actuate the VVT solenoid.
This information is also conveyed via the CAN databus to the instrument cluster, where the EOP warning light is turned on or off accordingly.
Engine Coolant Temperature (ECT) sensor
The ECT sensor is designed as an NTC resistor and is used to measure the exact ECT.
The PCM uses the signal from the ECT sensor to correct the following values:
- Determination of injection duration
- Engine idle speed
- Control of cooling fan
- Control of A/C compressor
A voltage of 5V is applied to the ECT sensor by the PCM. The PCM is able to determine the coolant temperature from the temperature-dependent voltage drop at the sensor.
If the signal from the ECT sensor fails, the cooling fan is on all the time and the A/C is turned off. When the ignition is switched on, the value from the IAT sensor is read. When the engine is running, the temperature is calculated using a temperature map stored in the PCM according to how long the engine has been running. This substitute value is then used as the basis for calculating the injected fuel quantity and the ignition timing.
Evaporative emission canister purge valve
The EVAP purge valve is only actuated by the PCM if the coolant temperature is at least 60°C. In that case the EVAP purge valve is opened and the vacuum in the intake manifold sucks ambient air through the activated charcoal in the evaporative emission canister. In this way the adsorbed hydrocarbons are led to the combustion chamber of the engine.
The EVAP purge valve is deactivated and purging of the system is halted as soon as the engine management system goes into idling and/or fuel adjustment mode.
Cooling fan module
The cooling fan module is directly supplied with battery power via a 60A fuse in the BJB. It is actuated via a PWM signal from the PCM depending on the operating state of the engine and the air-conditioning system.
The speed of the cooling fan motor is controlled according to this signal.
Power Steering Pressure (PSP) switch
The PSP switch registers pressure in the line between the power steering pump and the steering gear. When a predefined pressure is reached, the switch is opened, thereby allowing the PCM to stabilize the idle speed in good time.
If the PSP switch fails, this can lead to idling fluctuations which could cause the engine to stall in case of large steering deflections (when parking).
Injectors
The electromagnetically controlled injectors dose and atomize the fuel. The quantity of injected fuel is regulated by the duration of actuation of the fuel injectors. The fuel injectors are either closed (not actuated) or opened (actuated). Each cylinder has its own injector. The injection is accurately dosed and takes place at a time determined by the PCM. Injection takes place immediately in front of the intake valves of the cylinder.
3
Fuel inlet with fine sieve
7
Valve needle with solenoid armature
8
Valve seat with nozzle hole disk
The fuel injectors consist of a housing with fuel passages, a coil and an injector needle with a solenoid armature. The fuel inlet in the injector features a fine sieve. The injectors are controlled via end-stages integrated into the PCM with the signal calculated by the engine management system on the earth side. Power is supplied via the Powertrain Control Module relay and fuse F9 in the BJB. The injected fuel quantity depends on the opening time, the fuel pressure and the diameter of the nozzle holes. There are two holes in the nozzle hole disk. These are arranged so that two jets of fuel emerge. Each jet supplies one intake valve.
Electronic ignition coil
The electronic ignition system is a fully electronic, distributorless ignition system with no moving parts on the high-voltage side.
The electronic ignition system is integrated into the PCM.
With an electronic ignition system, high-voltage distribution to the individual cylinders is realized via special double spark coils. The signal from the CKP sensor forms the basis for ignition timing calculations. From an ignition map, the PCM determines the optimum closing time and current rise of the primary current circuit of the ignition coil with switching carried out via end-stages in the PCM. The ignition timing is determined by the PCM on the basis of the engine operating conditions. Once the ignition timing has been determined, the PCM interrupts the current supply to the primary circuit of the ignition coil, triggering a high voltage which causes a spark in the cylinder via the ignition cable and spark plug.
The spark plugs are activated in pairs (cylinders 1 and 4, and cylinders 2 and 3) and send a strong main spark to the cylinder in the compression cycle and a weak secondary spark to the cylinder in the exhaust cycle. The main spark is generated automatically in the cylinder that is in the compression cycle, because a higher resistance exists between the electrodes on account of the high compression.
On one spark plug a spark jumps across from the centre electrode to the earth electrode, and on the other spark plug from the earth electrode to the centre electrode.
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