System Components - Part 2

DESIGN

Main relay (system relay)



The function of the main relay (system relay) is to supply certain components with voltage. The relay is mechanical and has a closing function. In the rest position the circuit in the relay is open. The main relay terminals (#30 and #86) are supplied with voltage by the battery. When the ignition key has been turned and the engine control module (ECM) is powered, the terminal (#85) on the main relay is grounded by the engine control module (ECM). When the terminal (#85) is grounded, the relay is activated and a number of components are powered via the relay terminal (#87).

The engine control module (ECM) can diagnose the main relay.

The main relay is in the relaylfusebox in the engine compartment.

Air conditioning (A/C) relay



The air conditioning (A/C) relay controls the A/C compressor. when the climate control module (CCM) requests A/C control, a signal is transmitted to the engine control module (ECM) via the controller area network (CAN) to activate the relay. The engine control module (ECM) temporarily deactivates the relay in the event of:
full load acceleration
too high engine coolant temperature.

The relay is mechanical. It has a closing/breaking function and is supplied with power from the system relay.

In the rest position the circuit in the relay is open. The system relay supplies the coil and the relay with power. The relay activates when the coil is grounded in the engine control module (ECM), the circuit closes and the A/C compressor is supplied with power via the relay voltage output.

The relay coil is grounded (signal) when the engine control module (ECM) receives a signal via the Controller area network (CAN) from the climate control module (CCM) to activate the relay and start the compressor.

Fuel pump (FP) relay



The fuel pump (FP) relay supplies the fuel pump with power. The relay also cuts the power to the pump when the ignition is switched off or if the engine stops. The central electronic module (CEM) also cuts the power to the relay if the supplemental restraint module (SRS) transmits a message indicating that an airbag has deployed.

The central electronic module (CEM) activates and deactivates the relay when requested by the engine control module (ECM) (via the Controller area network (CAN)).

When the ignition is switched on, the engine control module (ECM) sends a signal to the central electronic module (CEM) via the controller area network (CAN) to run the fuel pump (FP) for one seconds. This is so that the pressure increases in the fuel system, shortening the start time.

When the flywheel in the engine rotates (generating a signal from the engine speed (rpm) sensor), the engine control module (ECM) will transmit a request to the central electronic module (ECM) via the Controller area network to start the fuel pump (FP). In the event of the engine stopping, the Engine Control Module (ECM) cancels the "activated fuel pump" signal. The central electronic module (CEM) then switches off the fuel pump (FP).

There is a directly connected cable between the engine control module (ECM) and the central electronic module (CEM). In the event of a fault in the Control area network (CAN), this cable is used by the "activated fuel pump" signal

Air distribution valve



Cars from model year 1999-2000 have an air distribution valve. The air distribution valve supplies the injectors with air. This results in better volumetric efficiency, more effective combustion and therefore cleaner exhaust emissions. The valve is also used for idle air trim but is also slightly open at higher engine speeds.

The valve is directly mounted on the inlet hose for the electronic throttle module (ETM). The valve is connected to a hose which supplies air to the air-shrouded injectors via a distribution pipe.

The valve has its own ignition driver stage and solenoid and is supplied with 12V. The valve is controlled steplessly by the Engine Control Module (ECM) using a variable pulse ratio (duty-cycle) which opens or closes a shutter in the valve.

The valve works primarily during cold starts and when idling, to minimize the release of carbon dioxide and hydro-carbons whilst maintaining performance and drivability. This is partly because the size of fuel drops is smaller with fuel mixed with air and does not adhere as easily to the walls of the intake manifold when they are cold and damp. This also reduces fuel consumption when cold starting and cuts the warm up time for both the engine and the three-way catalytic converter (TWC).

The total calculated volume of air to be released into the combustion chamber is distributed between both the Electronic Throttle Module (ETM) and the air distribution valve. The input signals to the Engine Control Module (ECM) which affect the operation of the air distribution valve are: the position of the throttle, engine speed (RPM)/position sensor, engine coolant temperature (ECT) sensor, ambient air pressure and ambient air temperature.

The engine control module (ECM) can diagnose the air distribution valve. The valve can be activated using VIDA.

Injectors



The function of the injectors is to spray fuel into the cylinders in the correct spray patterns. This happens sequentially.

The injectors are in the intake manifold.

It is essential that the injectors are correctly installed with no air leakage around them. Fuel leakage from the top of an injector when it is not activated may lead to starting and driving problems.

The engine control module (ECM) controls the injectors using a pulse width modulation (PWM) signal.

The engine control module (ECM) can diagnose the injectors. The injectors can be activated using VIDA.

Air-shrouded injectors
Cars from model year 1999-2000 have air-shrouded injectors.

The injectors are in the air distribution pipe which is in the intake manifold.

The lower section of the injectors has 2 openings in the side where air can enter.

When the needle in the injector starts to rise, the openings are exposed. This allows air to flow in to the center of the valve at high speed, and the fuel and air are finely distributed and mixed.

When the needle rises further, the injector nozzle opens and the air/fuel mixture is released into the combustion chamber.

Evaporative emission system (EVAP) valve



The evaporative emission system (EVAP) valve is used to open/close the connection between the EVAP canister and the intake manifold. The valve controls the flow of hydro-carbons (fuel vapor) from the EVAP canister to the engine intake manifold using the vacuum in the intake manifold. This ensures that hydro-carbons stored in the EVAP canister are used in the engine combustion process.

The valve is an electro-magnetic valve which is powered from the system relay. When the valve needs to be opened, it is grounded internally in the engine control module (ECM). The evaporative emission system (EVAP) valve is closed when in the standby position (open-circuit).

When the control module requests that the EVAP canister should be emptied (the hydrocarbons stored in the canister should be released into the engine), the control module deploys the evaporative emission system (EVAP) valve by grounding it. The valve is grounded using a pulse width modulation (PWM) signal, allowing the control module to govern the extent to which the valve opens and adapting the emptying of the canister according to how full it is, engine speed (rpm) and load etc.

The engine control module (ECM) can diagnose the evaporative emission system (EVAP) valve. The valve can be activated using VIDA.

The evaporative emission system (EVAP) valve is close to the intake manifold.

Camshaft reset valve (Continuous variable valve timing (CVVT))



The camshaft reset valve controls the oil flow to the continuous variable valve timing (CVVT) unit. The valve consists of an electro-magnetic valve with a spring-loaded piston. There are slits in the piston which channel the engine lubricating oil to different channels in the continuous variable valve timing (CVVT) unit by moving the piston in the reset valve. The continuous variable valve timing (CWT) unit turns the camshaft (the cam timing changes). The direction in which the camshaft turns depends on the chamber in the CWT unit which is supplied with oil (pressure).

The system relay supplies the reset valve with voltage. The valve is grounded (control stage) in the engine control module (ECM). When the valve is grounded using a pulse width modulation (PWM) signal, the oil flow in the valve can be controlled to the different chambers in the continuous variable valve timing (CVVT) unit at variable rates. This allow the angle of the camshaft to be changed precisely and smoothly.

The engine control module (ECM) has diagnostics for the reset valve. The value of the reset valve can be read using VIDA.

Only cars of model year 2000 and later have continuous variable valve timing (CVVT). The valve is on the cylinder head above the camshaft with camshaft control.

Ignition coils



The ignition coils ignite the fuel/air mixture on command from the engine control module (ECM). The signal is re-transmitted so that the control module knows that it worked.

Each ignition coil has its own integrated power stage. The ignition coils are in the sparkplug wells above each spark plug.

The engine control module (ECM) can diagnose the ignition coils. The ignition coils can be activated using VIDA.

Emissions warning lamp



The emissions warning lamp in the Driver Information Module (DIM) has a warning symbol. This warning symbol varies depending on the market and model year. The warning symbols are:
"Engine symbol" (not USA, model year 2001-)
"CHECK ENGINE" (MIL - Malfunction Indicator Lamp, USA only)
"Lambda symbol" (not USA, model year 1999-2000).

The warning symbol lights when the ignition key is turned to position II and goes out when the engine is started if the engine management system does not detect any faults.

The warning lamp is directly connected to the engine control module (ECM).

The warning lamp will light if there is a fault in one of the monitored parameters in the engine management system. The warning lamp will also light in response to a request transmitted via the Control area network (CAN) if there is a fault in one of the following systems which affects emissions:
transmission control module (TCM)
brake control module (BCM)
electronic throttle module (ETM).

Electronically control led throttle system



In addition to the engine control module (ECM), the electronically controlled throttle system consists of an electronic throttle module (ETM) and an accelerator pedal (AP) position sensor. The system does not have a mechanical link system or mechanical cable. The accelerator pedal (AP) position sensor generates two output signals: An analog signal which is approximately 0.5 V when idling and approximately 4.5 V at wide open throttle (WOT). There is also a pulse width modulated digital signal.

The engine control module (ECM) uses the input signal from the accelerator pedal (AP) position sensor to calculate the requested position of the throttle. The calculated signal, which corresponds to the requested air flow, is transmitted to the electronic throttle module (ETM) on the high-speed side of the Controller area network (CAN). The electronic throttle module (ETM) receives the signal and deploys the shutter in the module to the requested position. The electronic throttle module (ETM) transmits a signal (which corresponds to the actual position of the throttle) on the high speed side of the controller area network (CAN) back to the engine control module (ECM) to confirm that the electronic throttle module (ETM) has opened the throttle as requested.

Both the engine control module (ECM) and electronic throttle module (ETM) contain a micro-processor which controls the throttle based on requests from the engine control module (ECM). The micro-processors also diagnose and monitor their own and each other's function. When there is a fault, the micro-processors transmit a message to the driver information module (DIM) via the Controller area network (CAN) requesting that the emissions warning lamp lights. The electronic throttle module (ETM) consists of a damper motor and a throttle disc amongst other components. The throttle disc is mechanically connected to two potentiometers, which are mounted at each end of the throttle spindle.

The damper motor is supplied with 12 V and both potentiometers with 5 V.

For safety reasons, two potentiometers transmit the same signal about the position of the throttle to the electronic throttle module (ETM).

If the signal from one of the potentiometers is missing or faulty, the electronic throttle module (ETM) is still able to calculate the position of the throttle using the signal from the other potentiometer. This maintains the drivability of the car. However the throttle system will be in Limp-home mode and may react differently than normal.

At closed throttle position (CTP) the signal is approximately 0.1 V and at wide open throttle (WOT) it is approximately 4.8 V.

All signals between the engine control module (ECM) and the electronic throttle module (ETM) are transmitted via the Controller area network (CAN). A back-up signal is transmitted via a directly connected signal cable between the accelerator pedal (AP) position sensor and the electronic throttle module (ETM). However the cable runs via the engine control module (ECM).

A simple way to check that the electronic throttle module (ETM) is supplied with power is to switch on the ignition. Power is being supplied if the electronic throttle module (ETM) beeps. In addition there may be a clicking sound when the throttle disc is calibrated to the mechanical limit position.

The electronically controlled throttle system can be diagnosed by both the engine control module (ECM) and the electronic throttle module (ETM). However, the information is read off from the engine control module (ECM).

Manifold absolute pressure (MAP) sensor



The manifold absolute pressure (MAP) sensor detects quick pressure changes in the intake manifold after the throttle. The signal from the sensor is used by the engine control module (ECM) as an addition to the mass air flow (MAF) sensor to calculate the injection period.

The semi-conductor sensor is grounded in the control module and is supplied with power from the control module.

The resistance in the sensor changes depending on the pressure in the intake manifold, giving a signal of 0.5 - 4.5 V. Low pressure results in low voltage, high pressure in high voltage.

The engine control module (ECM) can diagnose the manifold absolute pressure (MAP) sensor. The signal can be read using VIDA.

The manifold absolute pressure (MAP) sensor is on top of the radiator and is connected to the intake manifold by a hose.

Fuel tank pressure sensor (certain markets only)



The fuel tank pressure sensor detects the pressure in the fuel tank. The signal from the sensor is used by the engine control module (ECM) during diagnostics to check for leakage in the fuel tank system. The sensor, which is a piezo resistor, is grounded in the control module and supplied with power from the control module.

The resistance in the sensor changes depending on the pressure in the fuel tank, giving a signal of 0.5 - 4.5 V. Low pressure results in low voltage, high pressure in high voltage.

The engine control module (ECM) can diagnose the fuel tank pressure sensor. The sensor signal can be read using VIDA.

The fuel tank pressure sensor is positioned on top of the fuel tank on cars with leakage diagnostics for the evaporative emission (EVAP) system.

EVAP canister shut-off valve (certain markets only)



The EVAP canister shut-off valve is used to close the connection between the EVAP canister/fuel tank system and fresh air (atmospheric pressure) when leak diagnostics are carried out on the cars with the evaporative emission (EVAP) system.

The valve is an electro-magnetic valve which is powered from the system relay. When the valve needs to be closed, it is grounded internally in the engine control module (ECM). The valve is open when in the rest position (open-circuit).

The engine control module (ECM) can diagnose the valve. The valve can be activated using VIDA. The valve is next to the EVAP canister on cars with leak diagnostics for the evaporative emission (EVAP) system.