LR3/Disco 3
Difficulty in starting or start - stall.
Poor throttle response / engine performance.
Lambda control and idle speed control halted.
Emissions incorrect.
AFM signal offset
The Inlet Air Temperature (IAT) sensor is integrated into the Mass Air Flow meter. It is a temperature dependent resistor
(thermistor), i.e. the resistance of the sensor varies with temperature. This thermistor is a negative temperature coefficient
(NTC) type element meaning that the sensor resistance decreases as the sensor temperature increases. The sensor
forms part of a voltage divider chain with an additional resistor in the ECM. The voltage from this sensor changes as the
sensor resistance changes, thus relating the air temperature to the voltage measured by the ECM.
The ECM stores a 25°C default value for air temperature in the event of a sensor failure.
MANIFOLD ABSOLUTE PRESSURE SENSOR (MAP)
The MAP sensor provides a voltage proportional to the absolute pressure in the intake manifold. This signal allows the
load on the engine to be calculated and used within the internal calculations of the ECM. The sensor is located on the
rear of the air intake manifold.
The output signal from the MAP sensor, together with the CKP and IAT sensors, is used by the ECM to calculate the
amount of air induced into the cylinders. This enables the ECM to determine ignition timing and fuel injection duration
values.
The MAP sensor receives a 5V supply voltage from pin 48 of ECM connector C0634 and provides an analogue signal to
pin 69 of ECM connector C0634, which relates to the absolute manifold pressure and allows the ECM to calculate engine
load. The ECM provides a ground for the sensor via pin 11 of ECM connector C0634.
If the MAP signal is missing, the ECM will substitute a default manifold pressure reading based on crankshaft speed and
throttle angle. The engine will continue to run with reduced drivability and increased emissions, although this may not be
immediately apparent to the driver. The ECM will store fault codes which can be retrieved using T4.
KNOCK SENSORS
Pin No Description
1
MAP signal
2
Sensor supply
3
Not used
4
Sensor ground
