DeVille DTS V8-4.6L VIN 9 (2002)
Engine Control Module: Description and Operation
General Description
POWERTRAIN CONTROL MODULE
The PCM verifies that the password received from the theft deterrent control module via the Class 2 serial data circuit is correct. The PCM can learn
only one enable password. If the enable password is correct, the PCM enables the starting and fuel delivery systems.
The PCM disables the starting and fuel delivery systems if any of the following conditions occur:
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The enable password is incorrect.
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The system disable password is sent by the theft deterrent control module.
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No passwords are received - there is no communication with the theft deterrent control module.
Powertrain
The powertrain used in this vehicle consists of a twin cam V8 engine mated to a 4T80-E transaxle. The powertrain has electronic controls to reduce
exhaust emissions while maintaining excellent driveability and fuel economy. The Powertrain Control Module (PCM) manages the operation of the
engine control system.
The PCM is designed to maintain exhaust emission levels to Federal or California standards while providing excellent driveability and fuel efficiency.
Review the components and wiring diagrams in order to determine which systems are controlled by the PCM. The PCM monitors numerous engine and
vehicle functions. The following are some of the functions that the PCM controls:
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Engine fueling
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Ignition Control (IC)
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Knock Sensor (KS) system
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Evaporative Emission (EVAP) system
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Secondary Air Injection (AIR) system (if equipped)
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Exhaust Gas Recirculation (EGR) system
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Automatic transmission functions
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A/C Clutch Control
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Cooling Fan Control
Powertrain Control Module Function
The PCM constantly looks at the information from various sensors and other inputs, and controls systems that affect vehicle performance and emissions.
The PCM also performs diagnostic tests on various parts of the system. The PCM can recognize operational problems and alert the driver via the
Malfunction Indicator Lamp (MIL). When the PCM detects a malfunction, the PCM stores a Diagnostic Trouble Code (DTC). The problem area is
identified by the particular DTC that is set. The PCM supplies a buffered voltage (5 V or 12 V) to various sensors and switches. The input and output
devices in the control module include analog to digital converters, signal buffers, counters, multiple function drivers, and output drivers. The multiple
function drivers (i.e., EGR Control, Fuel Pump Relay) are electronic switches that supply ignition voltage to energize the circuit. The output drivers are
electronic switches that, when energized, complete the ground path. Most PCM controlled components are operated via output drivers. The PCM
monitors these driver circuits for proper operation. In most cases, if a problem is detected, a DTC corresponding to the controlled device will set.
Torque Management
Torque Management is a function of the PCM that reduces engine power under certain conditions. Torque management is performed for three reasons:
1. To prevent overstress of powertrain components.
2. To limit engine power when brakes are applied.
3. To prevent damage to the vehicle during certain abusive maneuvers.
The PCM uses manifold vacuum, intake air temperature, spark retard, engine speed, engine coolant temperature, A/C clutch status, and EGR valve
position to calculate engine output torque. The PCM then looks at torque converter status, transaxle gear ratio, and brake switch inputs and determines if
any torque reduction is required. If torque reduction is required, the PCM retards spark as appropriate to reduce engine torque output. In the case of
abusive maneuvers, the PCM may also shut-off fuel to certain cylinders to reduce engine power.
There are five instances when engine power reduction is likely to be experienced
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During transaxle upshifts and downshifts.
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Heavy acceleration from a standing start.
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If brakes are applied with moderate to heavy throttle.
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When the driver is performing stress-inducing (abusive) maneuvers such as shifting into gear at high throttle angles.
In the first two instances, the driver is unlikely to even notice the torque management actions. In the other cases, engine power output will be moderate at
full throttle.
When the PCM determines that engine power reduction is required, the PCM calculates the amount of spark retard necessary to reduce power by the
desired amount. This spark retard is then subtracted from the current spark advance. In the case of abusive maneuvers, the PCM will momentarily disable
fuel injectors to obtain the necessary amount of torque reduction.
Traction Control
Traction control is a function of the PCM and electronic brake and traction control module (EBCM) to reduce wheel slip during acceleration. When
wheel slip is detected, the EBCM applies the front brakes, and the PCM reduces engine power. The PCM continuously sends the EBCM a PWM signal
