Powertrain Management: Description and Operation

Electronic Throttle
The electronic throttle assembly, in response to signals from both the driver and the ECM, adjusts idle speed, sets the throttle valve to the position requested by the driver's accelerator/throttle pedal, cruise and traction control, power limitation and catalyst warm-up.

Mass Air Flow Meter
The sensor is located in the air flow meter assembly and outputs an analogue voltage to the ECM. This sensor measures air flow into the engine intake system and is calibrated to measure kg/hour.

Intake Air Temperature
The intake air temperature sensor is located in the air flow meter assembly and outputs an analogue voltage to the ECM. The ECM will substitute a default value equal to 50°C should this sensor fail.

Fuel Injectors
The eight bottom fed fuel injectors are located in the fuel rails. The fuel injectors are electromagnetic solenoid valves controlled by the ECM. The pulse time for the injector combined with the fuel pressure determines the volume of fuel injected to the manifold.

Fuel Delivery
The fuel pump provides fuel to the fuel rail where the circulating pressure is controlled by a pressure regulator valve; excess fuel is returned to the fuel tank.
The pressure regulator valve is controlled by manifold depression so that fuel delivery pressure is maintained at approximately 3 bar above manifold pressure.

Fuel Pump Relay
The ECM controls this component for normal engine running. The security system may disable this relay via communication with the ECM.

Fuel Level Sensing
The tank fuel is measured by the fuel level sensor. This signal is used by the ECM as an input to certain diagnostics.

Evaporative Valve
Excess vapor formed in the fuel tank is absorbed into the evaporative emission purge control canister. While the engine is running, the fuel absorbed in the canister is gradually purged back into the engine. The rate of purging is governed by engine operating conditions and vapor concentration level. Operating conditions which affect the purge rate are:
Speed and load
Coolant temperature
Time elapsed from start up
Closed loop fueling
Determination of the vapor concentration is made by stepped opening of the EVAP valve and subsequent monitoring of the fueling correction. This function is performed prior to purging, so that at the onset of purging the EVAP valve can be set to the optimum position. Should the ECM be unable to determine the concentration before purging, a default value is employed, which is then modified whilst purging is in progress.
When the purging process is operational the ECM modifies the basic fueling calculation to maintain the correct air/fuel ratio.
Purging is inhibited during fuel cut-off and stability/traction control intervention.

Coolant Temperature Sensor
The sensor outputs a voltage to the ECM which decreases as temperature increases.

Cooling Fans
In response to engine coolant temperature and climate control system demand, the ECM will energize the cooling fans.

Climate Control Compressor
The ECM will allow the compressor clutch to be engaged if the engine temperature and load demand are normal. Should the driver require maximum engine power or the coolant temperature be high, the request will be denied.

Cranking Signal
The ECM reacts to a signal from the Body Processor Module (BPM) when the starter motor relay is energized. This signal is used to trigger starting, fuel and ignition strategies.

Engine Speed and Crankshaft Position
Engine speed and crank position are monitored by a sensor which is mounted on the cylinder block (flywheel housing) behind the crankshaft drive plate. It indicates rotational speed to the ECM in the form of 12 pulses per crank revolution. Engine speed is used for synchronization of fuel and ignition systems, as well as other functions.

Camshaft Position
The camshaft position sensor is mounted at the rear of Bank 2 cylinder head on the intake side and provides one signal every 720 degrees of crankshaft rotation. The signal, in conjunction with the signal from the crankshaft position sensor, indicates to the ECM that the piston of cylinder 1A is approaching TDC on the compression stroke.

Variable Valve Timing (Where Fitted)
By energizing a solenoid to allow the passage of pressurized oil on each of the intake camshaft drives, the ECM can vary by a single stepped amount, the relative timing of the inlet valves.

Ignition
Ignition spark is produced by individual on-plug coil units.
There are two ignition amplifiers; module #1 drives coils 1A, 2B, 3B & 4A, whilst module #2 drives coils 1B, 2A, 3A & 4B. The ECM controls the amplifiers.

Knock Sensor
This sensor uses a piezo-electric sensing element to detect knock which may occur under acceleration at critical conditions. Should detonation be present the ECM will retard ignition timing of individual cylinders.

Exhaust Gas Recirculation
The EGR valve (where fitted) reduces NOx emissions by recirculating a portion of the exhaust gases back into the intake manifold.

Heated Oxygen Sensors
The heated oxygen sensors, one per bank, are situated upstream of the catalysts. Integral to the sensors are heaters (under ECM control) which allow the sensors to reach their operating temperature as soon as possible after engine start. A comparison between the level of oxygen in the exhaust gas to that in the atmosphere produces an output signal. This signal is used by the engine closed loop fuel strategy to make fueling corrections and so control overall emission levels.

Oxygen Sensors
These sensors, one per bank, are situated downstream of the catalyst. The comparison of upstream and downstream signals allows determination of catalyst conversion efficiency.