Computer Control Components Description
Engine Control Module (ECM) - (up to 99MY)
The engine control module (ECM) prior to 99MY is a GEMS (Generic Engine Management System), it is located in a plastic moulded box behind the battery in the engine compartment.
The ECM has various sensors fitted to the engine to allow it to monitor engine condition The ECM processes these signals and decides what actions to carry out to maintain driveability, after comparing the information from these signals to mapped data within its memory.
Input/Output:
The black plastic case which houses the ECM protects it from sources of contamination including heat. The ECM itself is contained in a cast aluminium case. The ECM has 3 independent connectors totalling 90 pins, of which up to 66 are used, dependent on market variations.
18-pin black connector (C509):
This connector is used primarily for ECM power and earth connections.
NOTE: Voltages and other measurements given are approximations only. Actual values will depend on particular specification and will be effected by accuracy and calibration of the measurement tool used and impedances caused by harness wiring etc.
ECM Pin Details For Connector C509::
36-pin red connector (C507):
This connector is used primarily for sensor inputs to the ECM.
NOTE: Voltages and other measurements given are approximations only. Actual values will depend on particular specification and will be effected by accuracy and calibration of the measurement tool used and impedances caused by harness wiring etc.
ECM Pin Details For Connector C507::
ECM Pin Details For Connector C507 Continued::
36-pin black connector (C505):
This connector is used primarily for outputs to actuators and sensors driven by the ECM.
NOTE: Voltages and other measurements given are approximations only. Actual values will depend on particular specification and will be effected by accuracy and calibration of the measurement tool used and impedances caused by harness wiring etc.
ECM Pin Details For Connector C505::
ECM Pin Details For Connector C505 Continued::
Crankshaft position (CKP) sensor - (up to 99MY)
The crankshaft position sensor is the most important sensor on the engine. It is located in the left hand side of the flywheel housing and uses a different thickness of spacer for manual and automatic gearboxes. The signal it produces informs the ECM:
- the engine is turning
- how fast the engine is turning
- which stage the engine is at in the cycle
As there is no default strategy, failure of the CKP sensor will result in the engine failing to start. The fault is indicated by illumination of the malfunction indicator light (MIL) on North American specification vehicles.
The output signal from the CKP sensor is obtained from the magnetic path being made and broken as the reluctor ring teeth pass the sensor tip. The reluctor ring has 35 teeth and one missing tooth spaced at 10°intervals. The missing tooth is positioned at 20° after TDC.
Fault codes:
- P0335 - Crankshaft sensor circuit fault - no signal
- P0336 - Crankshaft sensor generating poor quality signal
Camshaft position (CMP) sensor - (up to 99MY)
The camshaft sensor is located in the engine front cover, between the belt pulleys. It is a Hall Effect device which produces four pulses for every two revolutions of the engine. The signal is used for two purposes, injector timing corrections for fully sequential fuelling and active knock control. The CMP sensor signal pulses are generated from four gaps on the cam wheel, one gap is smaller than the other three, consequently one of the pulses is longer than the others.
If the camshaft sensor fails, default operation is to continue normal ignition timing. The fuel injectors will be actuated sequentially, timing the injection with respect to top dead centre. Injection will either be correct or one revolution out of synchronisation. The fault is not easily detected by the driver. The fault is indicated by illumination of the malfunction indicator light (MIL) on North American specification vehicles.
Fault codes:
- P0340 - Camshaft sensor circuit fault or signal timing different from crankshaft sensor signal.
NOTE: It is physically possible to interchange the camshaft gear wheel fitted to pre-99MY and post-99MY vehicles. However, because the GEMS and Motronic Systems are incompatible, an incorrect camshaft signal will be received by the ECM and a P0340 fault code will result.
Mass air flow (MAF) sensor - (up to 99MY)
The 'hot wire' type mass air flow sensor is mounted rigidly to the air filter and is connected by flexible hose to the plenum chamber inlet. The MAF sensor is a hot wire anemometer. The main sensing element of the sensor is a heated wire, positioned in the stream of intake air. Changes in intake air flow changes the temperature, and hence resistance, of the wire. The ECM measures this change in resistance and calculates the amount of air flowing into the engine.
As there is no default strategy, failure will result in the engine starting, and dying when it reaches 550 rev/mm, when the ECM detects no MAF sensor signal. The fault is indicated by illumination of the malfunction indicator light (MIL) on North American specification vehicles.
Intake Air Temperature (IAT) sensor - (up to 99MY)
The IAT sensor is another resistive sensor, located in the body of the air cleaner. The sensor resistance varies with changes in air temperature. The signal from the IAT sensor is used to retard the ignition timing if the air temperature rises above 55° C. If the sensor is disconnected or failure occurs a default value will be used by the system. The default value selected will represent nominal operating conditions. The fault may not be evident to the driver, there may be slight power loss in high ambient temperatures. The fault is indicated by illumination of the malfunction indicator light (MIL) on North American specification vehicles.
Throttle Position (TP) sensor - (up to 99MY)
The throttle position sensor is mounted on the throttle body in line with the throttle plate shaft. The sensor is a variable resistor, the signal from which (0 - 5V) informs the ECM of the actual position of the throttle disc and the rate of change of throttle position. This information is used by the ECM for regulation of acceleration enrichment fuelling. Sensor failure will adversely affect the acceleration performance. The closed throttle voltage is continuously monitored and updated when engine conditions indicate that the throttle is closed.
The GEMS ECM performs a throttle potentiometer range check by cross checking with the measured air flow. If the two values do not correlate and fuelling feedback indicates that fuelling and therefore airflow is correct, the potentiometer is assumed to have failed. In the event that a fault is detected, GEMS supplies a default value dependent on air flow.
The throttle angle is also supplied to the gearbox ECM, the loss of this signal will result in poor gear change quality and loss of kickdown.
WARNING: If the throttle potentiometer is changed, it is necessary to reset the closed throttle voltage.
Fault codes:
- P0121 - Throttle potentiometer signal inconsistent with MAF, IACV, air temperature and engine rpm.
- P0122 - Throttle potentiometer circuit low input
- P0123 - Throttle potentiometer circuit high input
Engine Coolant Temperature (ECT) sensor - (up to 99MY)
The sensor is located at the top front of the engine, to the right of the alternator and in front of the plenum chamber.
The sensor comprises a temperature dependent resistive metal strip. The resistance of the strip varies considerably with coolant temperature, i.e. from 28K ohms at - 30° C to 90 ohms at 130° C. At 85° C the resistance is 300 ohms. The ECT sensor signal is vital to engine running, as the correct fuelling is dependent upon engine temperature i.e. richer mixture at low temperatures.
If the sensor is disconnected or failure occurs, a default value will be supplied to the system. The initial default value selected will be based on the value of the air intake temperature. This will increase to a nominal warmed up value over a given time, programmed for each default value. The fault may not be evident to the driver, there may be a hot restart problem. The fault is indicated by illumination of the malfunction indicator light (MIL) on North American specification vehicles.
Fault codes:
- P0116 - Coolant temperature sensor - falling temperature fault
- P0117 - Coolant temperature sensor circuit low range fault
- P0118 - Coolant temperature sensor circuit high range fault
- P0125 - Coolant temperature sensor - no warm-up fault
Knock Sensors (KS) - up to 99MY
The knock sensor produces an output voltage which is proportional to mechanical vibration caused by the engine. A sensor is located in each cylinder bank between 2/4 and 3/5 cylinders. The ECM calculates if the engine is knocking by taking camshaft and crankshaft sensor signals to determine the position of the engine in the combustion cycle.
The ECM can also work out exactly which cylinder is knocking and progressively retards the ignition on that particular cylinder until the knock disappears. It then advances the ignition to find the optimum ignition timing for that cylinder.
The ECM can simultaneously adjust the timing of each cylinder for knock. It is possible that all eight cylinders could have different advance angles at the same time. If the camshaft sensor fails, the knock control will be disabled.
Fault codes:
- P0331 - Continuous knock on bank B
- P0332 - Knock background noise low, bank B
- P0333 - Knock background noise high, bank B
- P0326 - Continuous knock on bank A
- P0327 - Knock background noise low, bank A
- P0328 - Knock background noise high, bank A
Note that coil 1 feeds cylinders 1 and 6, coil 2 feeds cylinders 5 and 8, coil 3 feeds cylinders 4 and 7, and coil 4 feeds cylinders 2 and 3. The resistance of the spark plug in the compression cylinder is higher than that in the exhaust cylinder and hence more spark energy is dissipated in the compression cylinder. Coil failure will result in a lack of ignition, resulting in a misfire in the related cylinders. The fault is indicated by illumination of the malfunction indicator light (MIL) on North American specification vehicles.
Idle Air Control (IAC) valve - up to 99MY
The idle speed control stepper motor is located on the side of the inlet manifold. Idle speed is controlled by the stepper motor, which comprises two coils, mounted to the throttle housing. When energised in the correct sequence, the coils move a plunger which opens or closes the throttle bypass valve controlling the quantity of idle air. The stepper motor controls idle speed by moving the plunger a set distance called a step. Fully open is 200 steps (180 steps for vehicles up to 97MY) and fully closed 0 steps. Failure of the stepper motor will result in low or high idle speed, poor idle, engine stall or non start. If the number of recorded steps changes beyond a set threshold (opening or closing) without a corresponding change in airflow, then a fault code will be stored. The GEMS diagnostics also check for short circuit conditions during normal stepper operation and open circuit during power down. Detected faults are indicated by illumination of the malfunction indicator light (MIL) on North American specification vehicles.
The stepper motor coil resistance is 53 ohms ± 2 ohms.
CAUTION: The pintle must not be moved by force.
Fault codes:
- P0506 - Low idle speed
- P0507 - High idle speed
- P1508 - IACV stepper motor open circuit
- P1509 - IACV stepper motor short circuit
Heated Oxygen Sensor (HO2S) - up to 99MY
The heated oxygen sensors consist of a titanium metal sensor surrounded by a gas permeable ceramic coating. Oxygen in the exhaust gas diffuses through the ceramic coaling on the sensor, and reacts with the titanium wire altering the resistance of the wire. From this resistance change the ECM calculates the amount of oxygen in the exhaust gas. The injected fuel quantity is then adjusted to achieve the correct air:fuel ratio, thus reducing the emissions of carbon monoxide (CO), hydrocarbons (HC), and oxides of nitrogen (NOx). Two HO2S sensors are fitted, one in each exhaust front pipe and positioned in front of the catalytic convertor. On North American specification vehicles, an additional HO2S sensor is fitted behind each catalytic converter. These additional sensors are used to monitor the operating efficiency of the catalysts. Note that if the wiring to these sensors is crossed, the vehicle will start and idle correctly until the sensors reach operating temperature. Then the ECM will read the signals from them and send one bank of cylinders very rich and the other very weak. The engine will misfire, have a rough idle and emit black smoke, with possible catalyst damage.
The oxygen sensors are heated to ensure rapid warm up and continued operation when the exhaust temperature may be below the working temperature of the sensor. Both the upstream sensor heaters and the downstream sensor heaters are connected in parallel. The heaters are directly driven from the GEMS ECM by a pulse width modulated (PWM) signal to enable temperature control of the heater to be achieved. When the sensor is powered up, the duty ratio of the PWM signal to the heater is started low and then increased over a period of approximately 30 seconds. This is to ensure the sensor is not heated up too quickly, which might cause the ceramic interior of the sensor to crack. The duty ratio of the heater signal may be altered during normal operation to maintain sensor temperature.
In the event of sensor failure, the system will default to 'open loop' operation. Fuelling will be calculated using signals from the remaining ECM inputs.
On North American Specification vehicles, a fault with any of the HO2S sensors is indicated by illumination of the malfunction indicator light (MIL). ECM diagnostics also use the Heated Oxygen Sensors to detect catalyst damage, misfire and fuel system faults.
CAUTION: Although robust within the vehicle environment, Heated Oxygen Sensors are easily damaged by dropping, excessive heat and contamination. Care must be exercised when working on the exhaust system not to damage the sensor housing or tip.
Fault codes:
- P0130 - Oxygen sensor circuit slow response, upstream sensor bank A
- P0136 - Oxygen sensor circuit slow response, upstream sensor bank A
- P0150 - Oxygen sensor circuit slow response, upstream sensor bank B
- P0156 - Oxygen sensor circuit slow response, upstream sensor bank B
- P0131 - Oxygen sensor circuit low voltage, upstream sensor bank A
- P0151 - Oxygen sensor circuit low voltage, upstream sensor bank B
- P0137 - Oxygen sensor circuit low voltage, downstream sensor bank A
- P0157 - Oxygen sensor circuit low voltage, downstream sensor bank B
- P0132 - Oxygen sensor circuit high voltage, upstream sensor bank A
- P0152 - Oxygen sensor circuit high voltage, upstream sensor bank B
- P0138 - Oxygen sensor circuit high voltage, downstream sensor bank A
- P0158 - Oxygen sensor circuit high voltage, downstream sensor bank B
- P0133 - Oxygen sensor circuit slow response, upstream sensor bank A
- P0153 - Oxygen sensor circuit slow response, upstream sensor bank B
- P0139 - Oxygen sensor circuit slow response, downstream sensor bank A
- P0159 - Oxygen sensor circuit slow response, downstream sensor bank B
- P1138 - Oxygen sensor problem with switching lean, sensor(s) for bank A
- P1158 - Oxygen sensor problem with switching lean, sensor(s) for bank B
- P1137 - Oxygen sensor problem with switching rich, sensor(s) for bank A
- P1157 - Oxygen sensor problem with switching rich, sensor(s) for bank B
- P1139 - Oxygen sensor circuit switching period too long bank A
- P1159 - Oxygen sensor circuit switching period too long bank B
- P1171 - System too lean bank A and bank B
- P1172 - System too rich bank A and bank B
- P0171 - System too lean bank A
- P0174 - System too lean bank B
- P0172 - System too rich bank A
- P0175 - System too rich bank B
- P1185 - Oxygen sensor heater circuit open circuit, upstream sensors
- P1186 - Oxygen sensor heater circuit short circuit, upstream sensors
- P1187 - Oxygen sensor heater circuit inferred open circuit, upstream sensors
- P1188 - Oxygen sensor heater circuit high resistance, upstream sensors
- P1189 - Oxygen sensor heater circuit inferred low resistance,upstream sensors
- P1190 - Oxygen sensor heater circuit low resistance, upstream sensors
- P1191 - Oxygen sensor heater circuit open circuit, downstream sensors
- P1192 - Oxygen sensor heater circuit short circuit, downstream sensors
- P1193 - Oxygen sensor heater circuit inferred open circuit, downstream sensors
- P1194 - Oxygen sensor heater circuit high resistance, downstream sensors
- P1195 - Oxygen sensor heater circuit inferred low resistance, downstream sensors
- P1196 - Oxygen sensor heater circuit low resistance, downstream sensors
- P0420 - Catalyst efficiency is low, bank A
- P0430 - Catalyst efficiency is low, bank B
Relays - (up to 99MY)
The engine management system employs four relays, which are all located in the main under bonnet fusebox.
Main Relay:
The main relay supplies the power feed to the ECM to feed the fuel injectors (8 amps) and air flow meter (4 amps). This relay is controlled by the GEMS ECM which has a second power feed. This enables the ECM to remain powered up after ignition is switched off. During this 'ECM power down routine' the ECM records all temperature readings and powers the stepper motor to the cold start position. Failure of this relay will result in the engine management ECM not being powered up, resulting in engine not starting due to absence of fuel and ignition.
Starter Motor Relay:
The starter motor relay is ignition key controlled and activated with the key in position 3 only. Releasing the key after cranking cuts supply to the relay and switches off the starter motor. Failure of this relay will result in the starter motor not working.
Ignition Relay:
The ignition relay supplies the power teed to the coils (6.5 amps), purge valve (1 amp, non-continuous) and heating elements of the HO2S sensors (8 amps, non-continuous). The relay is ignition key controlled, when the key is turned off, supply to the coils is immediately cut. Failure of this relay will result in no ignition.
Ignition switch sense:
This is used to initiate the power up and power down routines within GEMS. The input is supplied from the ignition relay. When the ignition is turned on, the ignition relay is enerigised and the GEMS ECM starts its power up routines and turns on the ECM main relay, the main power to GEMS and its associated system components. When the ignition is turned off, GEMS will usually maintain its powered up state for several seconds (up to 20 minutes in extreme cases when cooling fans are required) while it initiates its power down routine. On completion of the power down routine, the ECM main relay is turned off.
See EMISSION CONTROL, Description and operation. Description and Operation
Fault codes:
- P1440 - Purge valve stuck open.
- P0442 - Evaporative loss control system - small leak
- P0448 - Evaporative loss control system - major leak
- P0496 - Evaporative loss control system - major leak
- P0446 - Purge canister closure valve information
- P1447 - Purge canister closure valve - poor performance
Inertia Fuel Shut-off (IFS) Switch
The inertia switch isolates the power supply to the fuel pump in the event of sudden deceleration, as encountered during an accident. The inertia switch is located in the right hand side footwell behind an access flap. It is reset by depressing the central plunger at the top of the switch.
Electronic Automatic Gearbox Intricate - up to 99MY
Engine Torque Signal
The engine torque signal is calculated by the GEMS ECM and output to the gearbox ECU in a 12 volt PWM signal format. Warm up status of GEMS is passed on start-up for OBDII purposes.
Throttle Angle Signal
The throttle signal is output by the GEMS ECM to the gearbox ECU in a 12 volt PWM signal format. The signal is used to calculate when a gear change is necessary. If a fault occurs with this signal, then the gearbox ECU assumes a default throttle angle. The signal is also used to indicate engine temperature at starting.
Ignition Retard (Torque Reduction)
The gearbox ECU calculates the optimum shift point and in order to produce a smooth gear change, sends a torque reduction signal to the GEMS ECM which retards the ignition so reducing the engine torque to allow a smooth shift.
Engine Speed Signal
The engine speed signal is output to the gearbox ECU via the Body electronic control module (BeCM). The signal comprises a 12 volt square wave with 4 pulses for every engine revolution.
The following fault modes are possible:
- Harness wiring or connector faulty
- Power up problems
- Faulty gearbox ECU
Fault codes:
- P1775 - Gearbox has signalled a fault condition to the ECM
- P1776 - Gearbox ignition retard request duration fault
- P1777 - Gearbox ignition retard request line fault
See AUTOMATIC GEARBOX, Description and operation.