Fuel Management Components Descriptions
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::
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 Fuel Temperature (EFT) sensor - (up to 99MY)
The EFT sensor is located on the fuel rail by cylinders 3 and 5. The sensor measures the temperature of the rail rather than the fuel. The resistance varies with changes in temperature. The signal is used to increase the injection pulse time when undergoing hot restarts. When the fuel is hot, vapourisation can occur in the fuel rail and bubbles form in the injectors. Increasing the pulse time helps flush the fuel vapour away. An EFT sensor 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:
- P0181 - Fuel temperature sensor fault - reading invalid compared with water temperature
- P0182 - Fuel temperature sensor circuit low range fault
- P0183 - Fuel temperature sensor circuit high range 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
Fuel injectors - (up to 99MY)
A multiport Sequential Fuel Injection (SFI) system is used which utilises one injector per cylinder. Each injector comprises a small solenoid which is activated by the ECM to allow a metered quantity of fuel to pass into the combustion chamber. Due to the pressure in the fuel rail and the shape of the injector orifice, the fuel is injected into the cylinder in a fine spray which aids combustion. In the unlikely event of total injector failure or leakage which will cause a rich mixture, a misfire will occur in the affected cylinder. The fault is indicated by illumination of the malfunction indicator light (MIL) on North American specification vehicles.
Fault codes:
- P0201 - Injector circuit fault, cylinder 1
- P0202 - Injector circuit fault, cylinder 2
- P0203 - Injector circuit fault, cylinder 3
- P0204 - Injector circuit fault, cylinder 4
- P0205 - Injector circuit fault, cylinder 5
- P0206 - Injector circuit fault, cylinder 6
- P0207 - Injector circuit fault, cylinder 7
- P0208 - Injector circuit fault, cylinder 8
- P1201 - Injector circuit open or ground short, cylinder 1
- P1202 - Injector circuit open or ground short, cylinder 2
- P1203 - Injector circuit open or ground short, cylinder 3
- P1204 - Injector circuit open or ground short, cylinder 4
- P1205 - Injector circuit open or ground short, cylinder 5
- P1206 - Injector circuit open or ground short, cylinder 6
- P1207 - Injector circuit open or ground short, cylinder 7
- P1208 - Injector circuit open or ground short, cylinder 8
CAUTION: The injectors are extremely sensitive, they must not be dropped or contaminated.
CAUTION: When assembling the injector to the fuel rail, only use clean engine oil to aid assembly. DO NOT use petroleum jelly or other forms of grease, as this will contaminate the injector.
The injectors can be checked using a multimeter to test the resistance values:
- Injector resistance at 20° C 16.2 ohms ± 0.5 ohms
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
Fuel pressure regulator - (up to 99MY only)
The fuel pressure regulator is a mechanical device controlled by manifold depression and is mounted at the rear of the engine in the fuel rail. The regulator ensures that fuel pressure is maintained at a constant pressure difference to that in the inlet manifold. As manifold depression increases, the regulated fuel pressure is reduced in direct proportion. When pressure exceeds the regulator setting, excess fuel is spill returned to the fuel tank swirl pot which contains the fuel pick up strainer.
Failure of the regulator will result in a rich mixture at idle but normal at full load, or a rich mixture resulting in engine flooding, or a weak mixture. Although the fault will not illuminate the MIL, faults caused by the failure may be indicated.
Accumulator - (up to 99MY only)
Certain derivatives have an accumulator fitted into the feed line connection at the fuel rail. The purpose of this device is to damp out pulsations in the fuel system caused by the normal opening and closing of the injectors. These pulsations, called injector knock, may otherwise be detected inside the vehicle.
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.
Fuel Pump Relay:
The fuel pump relay is fed from the ignition relay and controlled by the ECM. The relay is activated in ignition key position 2 to prime the fuel system for a period of time controlled by the ECM. Failure of this relay will result in no fuel pressure.
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
Fuel Tank Pressure Sensor
This sensor is used on NAS vehicles with advanced evaporative emissions systems. The sensor is located in the fuel tank sender unit and is not a serviceable item. The GEMS ECM checks for any fuel system leaks through joints and holes, by measuring the pressure drop after the vent seal valve is shut. The diagnostic system performs out of range and validity checks.
The following failure modes are possible:
- Connector or harness open circuit
- Sensor earthing problem
- Blocked sensor
Certain failure modes may cause the 5V supply voltage which is shared with the throttle position sensor to be reduced to less than 1V.
Fault codes:
- P0451 - Fuel tank pressure sensor poor performance fault
- P0452 - Fuel tank pressure sensor low range fault
- P0453 - Fuel tank pressure sensor high range fault
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.