Functions
Engine Control Module
The engine management system is controlled by the Engine Control module (ECM), which is installed in the control module enclosure in the engine compartment. The ECM provides optimum control of the engine under all operating conditions. It also incorporates a comprehensive monitoring and diagnostic capability. Software variations ensure that the system complies with the latest diagnostic and emissions legislation of the destination market.
The ECM receives inputs from engine related sensors and various vehicle systems, and provides outputs for the following:
- Electronic Throttle
- Fuel Pump
- Fuel Injection
- Ignition
- EVAP System
- Variable Valve Timing
- EGR System (where equipped)
- Engine Starting
- HO2S Heaters
- Instrument Cluster
- A/C Compressor Clutch
- Windshield and Backlight Heaters
- Radiator Cooling Fans
- Diagnostics
Cruise Control
The ECM operates the vehicle cruise control system, in all forward gears, in response to driver inputs through the master, SET+, SET-, CANCEL and RES switches.
Stability/Traction Control
If the CAN-TORQUE REDUCTION THROTTLE message from the brake control module requests torque reduction, the ECM reduces the throttle valve opening. It also changes the CAN-TRACTION ACKNOWLEDGE message to confirm that torque reduction is in progress.
Engine Power Limiting
If the TCM detects a fault in the transmission, it changes the CAN-TRANSMISSION OVERLOAD message to request an engine torque limit. The ECM then limits throttle valve opening to 18° maximum in all forward gears.
Vehicle Speed Limiting
The ECM uses throttle control to limit the vehicle's maximum speed to 248 km/h (155 mph).
Reverse Gear Torque Reduction
When reverse gear is selected the CAN-TRANSMISSION OVERLOAD message from the TCM requests an engine torque limit. The ECM then limits throttle valve opening to 18° maximum.
Fuel Pump
An output from the ECM controls the relay that operates the fuel pump. At ignition on, the pump will operate for 2 seconds without the ignition switch being set to crank, after which time the pump will be de-energized. Similarly, if the engine stops with the ignition on, the pump will be de-energized after 2 seconds. The pump operates continuously while the ignition switch is set to crank, or to on with the engine running. Supercharged vehicles are equipped with 2 fuel pumps that are operated together.
Fuel Injection
The ECM operates eight injectors to provide the engine with fuel. The amount of fuel required is determined from a base air:fuel ratio which is then adjusted for specific operating conditions. The ECM varies the number and duration of injector pulses per engine cycle to regulate the fuel flow. Injector timing is synchronized with engine rotation, except during starting and acceleration.
Feedback signals from the two HO2S in the vehicle's exhaust system enable the ECM to exercise closed loop fueling control and adaptive fueling. Separate channels in the ECM control each bank of injectors.
Adaptive fueling accommodates engine efficiency variations, system tolerances and engine ageing. Adaptations are produced at idle speed and four other points through the RPM/load range, on a fully warm engine, when the adaptive fueling function centralizes the feedback range. The ECM retains the adaptations in memory, for use in subsequent driving cycles. If the difference between the new and previous adaptations is excessive, a DTC is logged in the ECM memory. If the battery supply to the ECM is disrupted (eg. battery disconnection), the adaptations are lost from memory. On restoration of the battery supply, engine operation may be uneven until the adaptations are restored, especially at idle speed. The two 02S in the vehicle's exhaust system provide inputs which enable the ECM to monitor the efficiency of the downpipe catalytic converters. These inputs also enable the ECM to modify the HO2S inputs, to optimize the life of the catalytic converters.
Base Fuel Map
The ECM contains a base fuel map that corrects the base air:fuel ratio to the optimum mixture for a nominal engine throughout the engine speed and load ranges.
Battery Voltage Correction
Fuel flow through the injectors changes with voltage, so the ECM monitors their supply voltage and compensates for any variation from the nominal.
Starting
The fueling start strategy operates independent of accelerator pedal position or movement, with the exception of a wide open throttle. The ECM produces steady state running at the target idle speed within 2 seconds of firing, after an overshoot of 200 to 300 RPM maximum.
If the accelerator pedal demands a wide open throttle during cranking, the ECM disables fuel injection (and signals the throttle valve to the fully open position) to clear the fuel vapor from a "flooded" engine.
Warm-up Enrichment
During engine warm-up, the ECM determines the fuel required from maps which modify an enrichment factor for coolant temperature, engine speed and load.
Transient Fueling
During acceleration and deceleration, the ECM adjusts fueling to optimize the air:fuel ratio for exhaust emission, response and economy. This function operates over the full temperature range for all acceleration and deceleration rates.
Full Load Enrichment
At full load, the ECM inhibits closed loop fueling and increases the fuel supply to enrich the air:fuel ratio. Full load is derived from throttle valve position and engine speed. The degree of enrichment is dependent on engine speed.
Over-run Fuel Cut-off
When the throttle is closed at high engine speeds, the ECM disables fuel injection until the engine is at a lower speed. The speeds at which fuel injection is disabled and re-instated are mapped against coolant temperature.
On re-instatement the ECM uses a lean air:fuel ratio, to provide a smooth transition between the two states, which it then progressively returns to the nominal. The initial injector pulses are given a correction value to compensate for cylinder wall wetting. The ECM derives the air:fuel ratio for reinstatement from throttle valve position and engine speed.
During over-run fuel cut-off, operation of the EVAP valve, EGR valve (where fitted) and closed loop fueling are inhibited.
Engine Overspeed Protection
The ECM disables fuel injection if engine speed reaches 7100 RPM. Fuel injection is re-instated when RPM falls to 7050.
Stability/Traction Control
If the CAN-FAST TORQUE REDUCTION CYLINDER message from the BCM requests fuel intervention, the ECM reduces engine torque by disabling fuel injection until the throttle valve reaches its required torque reduction position. It also changes the CAN-TRACTION ACKNOWLEDGE message to confirm that torque reduction is in progress.
Ignition
The ECM supplies two ignition amplifier modules, which each supply four spark plug mounted ignition coils. The ECM varies the ignition timing to optimize power, emissions and driveability at all operating conditions.
A diagnostic signal from each amplifier module enables the ECM to monitor the supply to each ignition coil. If the ECM detects a failure it disables fuel injection to the affected cylinder.
Base Ignition Map
A base ignition map contains optimum timing for a nominal engine throughout the engine speed and load ranges. Corrections are then added to adjust for specific operating conditions.
Temperature Corrections
Corrections are added to the ignition timing to compensate for variations in intake air temperature and engine coolant temperature.
Knock Control
Between 700 and 6800 RPM, the ECM retards the ignition timing of individual cylinders if it detects detonation. Also, during acceleration at critical load and speed conditions, the ECM retards the ignition timing to prevent the onset of detonation.
Full Load Advance
At full load, the ECM advances the ignition timing at the same time as fuel enrichment is applied. The degree of advancement is dependent on engine speed.
Fuel Cut-off Interaction
Immediately prior to over-run fuel cut-off, the ECM retards the ignition timing to provide a smooth transition between the two states. On fueling re-instatement the ECM progressively returns the ignition timing to the nominal.
Throttle valve position and engine speed determine the rate at which the timing is returned to the nominal.
Starting
The ECM incorporates separate timing values for starting.
EGR (Where Equipped)
The ignition timing is advanced while the EGR system is active. The degree of advancement is dependent on engine speed and load.
Gear Shift Management
When the TCM decides a gear shift is necessary, it requests a percentage torque reduction using the CAN-TORQUE REDUCTION REQUEST message. The ECM then retards the ignition timing sufficient to achieve the torque reduction requested. As the ECM retards the ignition, it changes the CAN-TORQUE REDUCTION ACKNOWLEDGE message to the TCM to trigger the gear shift.
Transient Interaction
A correction is applied to the ignition timing during throttle transients. The correction is against rate of change for both opening and closing of the throttle.
Stability/Traction Control
If the CAN-FAST TORQUE REDUCTION IGNITION message from the BCM requests ignition intervention, the ECM retards the ignition by the amount requested until the throttle valve reaches its required torque reduction position. It also changes the CAN-TRACTION ACKNOWLEDGE message to confirm that torque reduction is in progress.
EVAP System
The ECM operates the EVAP valve to purge the fuel vapor from the carbon canister. Purge rates (ie. the amount the EVAP valve opens) are a function of engine operating conditions and the vapor concentration level.
The engine operating conditions that affect the purge rate are:
- speed and load
- coolant temperature
- time from start-up
- closed loop fueling
To determine the vapor concentration level, the ECM applies stepped opening signals to the EVAP valve and monitors the subsequent fueling correction. This is usually performed prior to purging, so that when purging starts, the EVAP valve can immediately be set to the optimum position. If the ECM is unable to determine the vapor concentration before purging, it uses a default value which it then modifies while purging is in progress. During purging, the ECM applies a correction to the basic fueling calculation based on the vapor concentration level.
Purging is inhibited during fuel cut-off and stability/traction control fueling intervention.
Variable Valve Timing
The ECM energizes the valve timing solenoids to advance the intake valve timing and de-energizes them to retard it.
The ECM uses engine load and speed maps to decide when to advance and retard the timing. The maps incorporate hysteresis for both engine load and speed to prevent "hunting".
Between 1250 and 4500 RPM (nominal), at engine loads greater than approximately 25% of the maximum, the timing is advanced. At low engine loads and at the two ends of the RPM range, the timing is retarded.
System operation is inhibited at engine coolant temperatures below -10°C (14°F). System operation is monitored using the input from the camshaft position sensor. If a fault is detected the ECM defaults to the retarded (de-energized) condition.
EGR System (Where Equipped)
The ECM operates the 4 pole stepper motor in the EGR valve to control the recirculation of exhaust gases. Unlike previous systems, there are no temperature or position feedback signals from the valve. The ECM monitors EGR operation using changes of mass air flow.
Engine Starting
At ignition on, if the gear selector is in Park or Neutral, the ECM enables the fuel injection and ignition functions. It also outputs a hard wired digital security acknowledge signal to the BPM to enable engine cranking. While the engine cranks, the BPM outputs a hard wired digital engine cranking signal to the ECM, which employs engine starting strategies for the duration of the signal.
If the gear selector is not in Park or Neutral at ignition on, the ECM inhibits the fuel injection and ignition functions, and withholds the security acknowledge signal to prevent cranking.
HO2S Heaters
The ECM energizes the heater elements of the HO2S during engine warm-up to shorten the time it takes for them to produce accurate outputs.
Instrument Cluster
The instrument cluster uses CAN messages from the ECM to operate the trip computer, tachometer, engine coolant temperature gauge and the BRAKE, CHECK ENG and general warning lamps.
Note: The CHECK ENG lamp is commonly known as the MIL.
AIR Compressor Clutch
Operation of the A/C compressor clutch is controlled by the ECM, to prevent unnecessary loads on the engine during unfavorable operating conditions.
On receipt of an A/C request signal from the A/C CM, the ECM immediately energizes the A/C compressor clutch relay provided the engine is not at idle speed, the coolant temperature is not above 119°C (246°F) and the throttle valve is not fully open When the A/C compressor clutch relay energizes, the relay output is sensed by the A/C CM, confirming that the A/C compressor clutch is engaged.
If the engine is at idle speed, the coolant temperature is above 119°C (246°F) or the throttle is fully open, the ECM outputs a load inhibit signal to the A/C CM and delays energizing the A/C compressor clutch relay. At idle speed the delay is only momentary (in the order of 50 ms) while idle speed compensation is implemented, after which the load inhibit signal is removed. At coolant temperatures above 119°C (246°F) or with a fully open throttle, the delay is for the duration of the inhibiting condition.
Similarly, with the A/C compressor clutch relay already energized, if the engine coolant temperature exceeds 119°C (246°) or the throttle goes to fully open, the ECM de-energizes the A/C compressor clutch relay and outputs the load inhibit signal to the A/C CM until the inhibiting condition is removed.
Windshield And Backlight Heaters
When the windshield heaters and/or the backlight heater are requested on, the A/C Control Module sends a screen request signal to the ECM. Provided the engine is not at idle speed, the coolant temperature is not above 119°'C (246°F) and the throttle valve is not fully open, the ECM takes no action and the A/C control module subsequently energizes the heaters.
If the engine is at idle speed, the coolant temperature is above 119°'C (246°F) or the throttle is fully open, the ECM outputs the load inhibit signal (the same one as used for the A/C compressor clutch operation) to the A/C CM to delay energizing the heaters. At idle speed the delay is only momentary while idle speed compensation is implemented, after which the load inhibit signal is removed. At coolant temperatures above 119°C (246°F) or with a fully open throttle, the delay is for the duration of the inhibiting condition.
Similarly, with the heaters already energized, if the engine coolant temperature exceeds 119°C (246°F) or the throttle goes to fully open, the ECM outputs the load inhibit signal to the A/C CM and the heaters are de-energized until the inhibiting condition is removed.
Radiator Cooling Fans
The ECM monitors inputs from the A/C single and triple pressure switches, and from the ECT sensor on the engine, to control the operation of the two radiator cooling fans. Outputs from the ECM control two relays contained in the radiator fans module, to operate the fans in off, slow or fast mode. In the slow mode the fans are connected in series; in the fast mode the fans are connected in parallel. Hysteresis in the temperature and pressure switching values prevents "hunting" between modes.
To counteract the increase in engine coolant temperature that occurs after the engine stops, at ignition off:
- if the fans are already on, the ECM keeps them on for 5 minutes, or until the ECT decreases to a pre-determined value, whichever occurs first
- if the fans are off, the ECM determines, from ECT and intake air temperature inputs, if the fans need to be switched on. If they do, it switches them on for 5 minutes, or until the ECT decreases to a pre-determined value, whichever occurs first.
Radiator Fan Switching Points
Fan Speed Coolant Temperature
Slow: On 90°C (194°F)
Off 86°C (187°F)
Fast: On 97°C (207°F)
Off 93°C (200°F)
Fan Speed A/C System Pressure
Slow: On 12 Bar (174 psi)
Off 8 Bar (116 psi)
Fast: On 22 Bar (319 psi)
Off 17.5 Bar (254 psi)
Diagnostics
The ECM performs self test routines and monitors engine functions, inputs and outputs to ensure correct operation of the engine and the engine management system. Hard wired inputs and outputs are monitored for short and open circuits, and sensor inputs are also monitored for range.
Additional checks are run on the more critical sensor inputs to ensure their validity. Some of the more critical inputs have substitute or default values which the ECM adopts if the input is diagnosed as faulty.
Any faults detected are logged in the ECM memory as DTC. The ECM also outputs engine malfunction messages on the CAN and adopts a default mode of operation. Most default modes retain some degree of engine operation (limp home).
The ECM also stores OBD II related DTC detected by other control modules on the CAN. Non-OBD II related DTC are retained in the memory of the control module that detects the fault.
To prevent false DTC being logged, the monitoring of some inputs and engine functions is inhibited while the vehicle is above a given altitude:
- at altitudes of 2438m (8000ft) and above,the ECM inhibits diagnostics on: EGR valve and EGR flow; EVAP valve and EVAP purge flow; idle speed control; misfire detection; catalytic converter efficiency.
- at altitudes of 2652m (8700ft) and above, the ECM also inhibits diagnostics on: HO2S; MAFS; 02S.