Part 1

Design

Ignition switch




The Engine Control Module (ECM) uses the signal from the ignition switch to detect when the ignition key has been turned to position II or III. When the key is in the ignition position (position II) or starting position (position III) a high signal (Ubat) is transmitted from the ignition switch to the engine control module (ECM). The engine management system prepares for start-up (for example, temporarily activates the fuel pump (FP) relay). When the flywheel in the engine rotates, the engine speed (RPM) sensor signal is used to keep the fuel pump (FP) relay activated.
The fuse in the fusebox in the passenger compartment supplies current to the ignition switch.
The central electronic module (CEM) can diagnose the ignition switch.

Brake lamp switch




The stop lamp switch is on the pedal box by the brake pedal. Its task is to supply the Engine control module (ECM) and Electronic throttle module (ETM) with information about the position of the brake pedal, if it is released or depressed.
One pin for the stop lamp switch is connected to battery voltage (terminal 30), the other pin is connected to the Engine control module (ECM) and the Electronic throttle module (ETM). When the brake pedal is in the released position, the stop lamp switch circuit is open, which means that 0 V is sent to the Engine control module (ECM) and the Electronic throttle module (ETM). If the brake pedal is depressed, the stop lamp switch circuit closes and battery voltage is sent instead.

The information from the stop lamp switch is used:
- together with information from the brake pedal position sensor to determine when it is permitted to use cruise control or not
- to determine whether the information from the brake pedal position sensor is valid or not.
- when the CAN does not work, to be the only information to the Electronic throttle module (ETM) about the position of the brake pedal.
To determine whether the information from the stop lamp switch can be used or not, the Engine control module (ECM) and the Electronic throttle module (ETM) carry out plausibility checks.
For further information about which tests are carried out, see diagnostic trouble code (DTC) information for the relevant diagnostic trouble code (DTC).

brake pedal position switch




The brake pedal position sensor is mounted on the power brake booster in the engine compartment. Its task is to supply the Engine control module (ECM) with information about the position of the brake pedal.
The brake pedal position sensor is affected by the brake pedal push rod and is a sliding potentiometer. The sensor is supplied with 5 V from the engine control module (ECM) and the signal that varies depending on the position of the brake pedal is sent to the engine control module (ECM).
When the pedal is released the signal is 3 - 4.5 V, the precise value depends on the engine control system in the vehicle. The reason that the signal differs between different engine control systems, despite it being the same sensor, is that the control module's internal circuits differ, which affects the signal level from the sensor. When the pedal is depressed, the voltage from the sensor drops.
From model year 2002 the brake pedal position sensor is directly connected to the brake control module (BCM), information is sent over the CAN to the Engine control module (ECM).

The information from the brake pedal position sensor is used:
- together with information from the stop lamp switch to determine when it is permitted to use cruise control
- to determine whether the information from the stop lamp switch is valid or not.
To determine whether the information from the stop lamp switch can be used or not, the Engine control module (ECM) and the Electronic throttle module (ETM) carry out an electrical check of the circuits and plausibility checks.
For further information about which tests are carried out, see diagnostic trouble code (DTC) information for the relevant diagnostic trouble code (DTC).

Accelerator pedal (AP) position sensor




The accelerator position sensor is mounted by the pedal box in the passenger compartment and makes a mounting for accelerator pedal. Its main task is to supply the Engine control module (ECM) with information about the position of the accelerator pedal.
The accelerator pedal position sensor consists of two internal sensors, where one generates an analog signal and the other a pulse width modulated signal (PWM). The purpose of having two types of sensor is to eliminate the probability of a fault from both signals from the sensors being incorrect, at the same time as them showing the same pedal position and the control module considers them correct.
The analog sensor supplies the Engine control module (ECM) with a signal that is approximately 0.5 V when the pedal is released and approximately 4.5 V when fully depressed. The sensor receives a voltage supply (5 V) and ground from the Engine control module (ECM).
The pulse width modulated (PWM) sensor supplies both the Engine control module (ECM) and Electronic throttle module (ETM) with a signal that has a fixed frequency of approximately 200 Hz where the pulse ratio varies between 8-88 %, depending on the position of the accelerator pedal.
The sensor receives voltage supply (12 V) via the main relay and is grounded via its own ground terminal. the signal to the Electronic throttle module (ETM) is electrically routed via the Engine control module (ECM), however, without affecting the signal at all.




The Engine control module (ECM) first uses the analog signal from the accelerator position sensor to calculate the desired throttle angle. The Engine control module (ECM) then transmits this request about the desired throttle angle via the CAN to the Electronic throttle module (ETM), which then fulfils the desired throttle angle and transmits back the information about the current throttle angle.
The pulse width modulated signal is used to monitor the analog signal. If there is a fault in the analog signal, the system uses the pulse width modulated (PWM) signal instead.
There are also situations when the PWM signal is used to control the throttle angle without a fault being detected on the analog signal. For example, when a fault has occurred in CAN communication between the Engine control module (ECM) and the Electronic throttle module (ETM), the throttle unit then does not receive any desired throttle angles from the Engine control module (ECM) but must then rely on the directly connected PWM signal to control the throttle.
On vehicles equipped with an automatic transmission, the sensor also contains a mechanical kick-down resistor that gives the driver a kick-down feeling when the pedal is depressed approximately 80 % of full pedal stroke. In this pedal position, the Transmission control module (TCM) permits kick-down to be activated. There is no separate switch in this sensor for kick-down.
To determine if the analog and the PWM signal are fault free, the Engine control module (ECM) and Electronic throttle module (ETM) carry out electrical checks and plausibility checks of the signals. If a fault is detected on any of the signals, the system uses the other signal.
For further information about which tests are carried out, see diagnostic trouble code (DTC) information for the relevant diagnostic trouble code (DTC).

Clutch pedal position sensor (manual transmissions only)




The clutch pedal position sensor is mounted between the clutch pedal and the pedal box. Its task is to supply the Engine control module (ECM) with information about the position of the clutch pedal.
The clutch pedal position sensor is a slide potentiometer and is supplied with 5 V from the Engine control module (ECM). The signal that varies depending on the position of the clutch pedal is sent to the Engine control module (ECM). When the pedal is released the signal is 3-4 V, the precise value depends on which engine control system the vehicle has. The reason that the signal differs between different engine control systems, despite it being the same sensor, is that the control module's internal circuits differ, which affects the signal level from the sensor. When the pedal is depressed, the voltage from the sensor drops.

The information from the clutch pedal position is used:
- to determine when it is permitted to use cruise control
- on certain markets to prevent the engine from being started if the pedal is released.
To determine if the information from the clutch pedal sensor can be used or not, the Engine control module (ECM) carries out an electrical check of the circuits and plausibility checks of the signal.
For further information about which tests are carried out, see diagnostic trouble code (DTC) information for the relevant diagnostic trouble code (DTC).

Electronic throttle unit




The throttle unit is mounted on the engine intake manifold, the location can vary depending on engine type. 5 cylinder turbocharged engines and 6 cylinder engines have the throttle unit mounted under the intake manifold. Others have it mounted on the side of the intake manifold. The throttle unit's primary task is to control the amount of air to the engine from the request from the Engine control module (ECM).
The Electronic throttle module (ETM) is in the throttle unit, which means that it works as its own control module on the high speed side of the CAN.
The connection to the CAN takes up two of the six pins in the throttle unit's connector, the remaining four are taken up by:
- Voltage supply, 12 V via the engine control system's system relay.
- Ground terminals, separated from the engine control system's other ground terminals.
- Information about the brake pedal's position from the brake lamp switch.
- Information about the position of the accelerator pedal from the accelerator pedal unit's PWM sensor.
In order for the Electronic throttle module (ETM) to carry out the main task of controlling the air flow to the engine, the voltage supply, ground and contact with the CAN is sufficient. The other two signals about the position of the brake pedal and the accelerator pedal are used as a safety function in case a problem should occur with CAN communication. This makes it possible to continue driving, but with reduced driveablity. The signals are used, among other things, to carry out a plausibility check of the desired throttle angle that comes from the Engine control module (ECM) via CAN.
In addition, the throttle unit consists of a further number of components such as throttle housing, throttle disc, throttle spindle, torque motor, throttle position sensor (potentiometers), spring unit etc.
In one end the throttle unit contains a stepless torque motor that is directly operated on the throttle spindle. The torque motor is supplied with 12 V and controlled by the Electronic throttle module (ETM). In the other end there is the throttle's spring unit and the mechanical stop for the smallest and largest throttle openings.




Outside the torque motor and the spring unit, out on the relevant end there is a throttle position sensor (potentiometer). The two position sensors are mechanically connected to each other via the throttle spindle.




1. Rotational hub with contacts.
2. Contacts, x 2
3. Contact track, 2 grooves.
For safety reasons, two position sensors send the same signal about the position of the throttle to the electronic throttle module (ETM).
If the signal from one of the position sensors 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 position sensor. This maintains the driveablity of the car.
Depending on the type of fault, the throttle system can reconfigure its own software (limp-home mode) and can react in different ways.
The throttle is a so called "ball zone throttle" which means that the throttle housing's mating surfaces are "spherical" and provide a better solution per opening angle. This gives more accurate flow control from idling position up to approximately 20 % open throttle. The effect is a smoother start at throttle opening / acceleration.
A number of plausibility checks are carried out by the Engine control module (ECM) to determine whether the throttle unit and Electronic throttle module (ETM) works as intended or not.
For further information about which tests are carried out, see diagnostic trouble code (DTC) information for the relevant diagnostic trouble code (DTC).

Electronically controlled throttle system




There are a number of components that are important for the electronic throttle system to work, the most vital parts are the Engine control module (ECM), Electronic throttle module (ETM) and the accelerator pedal position sensor. The system does not have a mechanical link system or mechanical cable.




The main task of the throttle unit system is to regulate the amount of air to the engine from the driver's demands. The driver requests a certain toque from the engine by depressing the accelerator pedal. This information is received by the Engine control module (ECM) that, together with the torque request from other functions, calculates a desired throttle angle.
The torque request from other functions means that there are loads that the system compensates for without the driver knowing it, for example, when the AC compressor is to be switched on, the throttle needs to be opened to compensate for the extra load that is placed on the engine. If the system does not do this, the engine speed would drop and the torque out on the drive shaft would be reduced every time the AC compressor was switched on, and increase when switched off.
The Engine control module (ECM) sends the request about the desired throttle angle to the Electronic throttle module (ETM) via CAN. The Electronic throttle module (ETM) fulfils the desired throttle angle and sends the information about the current throttle position back to the Engine control module (ECM) via CAN.
The Electronic throttle module (ETM), must not, under any circumstances, start to regulate the throttle position from its own request, but must always fulfill the desired throttle angle from the Engine control module (ECM). All signal transfers between the Engine control module (ECM) and Electronic throttle module (ETM) occur via CAN. If there is a problem with CAN communication, the information about the position of the accelerator pedal and the brake pedal is available via direct contact with the relevant sensor. This means that the vehicle can be driven, but with reduced driveablity. In this position, the Electronic throttle module (ETM) only controls the throttle position after the accelerator pedal position, the throttle unit does not know whether the engine is running or not.
The Engine control module (ECM) and Electronic throttle module (ETM) carry out checks and plausibility checks continuously. If a fault is detected, the system carries out corrective actions, such as to activate a suitable reconfiguration and store diagnostic trouble codes (DTCs).
For further information about which tests are carried out, see diagnostic trouble code (DTC) information for the relevant diagnostic trouble code (DTC).
Below is general information about diagnostic trouble codes (DTCs) and a more detailed explanation regarding reconfigurations in the throttle system.
General information
When the Electronic throttle module (ETM) detects that the communication to the Engine control module (ECM) is interrupted in any way or broken, faults are stored in the Electronic throttle module (ETM). The information about these faults are sent to the Engine control module (ECM) as soon as communication is restored on the CAN. This means that the Engine control module (ECM) stores the diagnostic trouble codes (DTCs) for these faults as soon as the Electronic throttle module (ETM) delivers the faults. This, in turn, means that it is at this point that the frozen values for the diagnostic trouble codes (DTCs) are saved. For the Electronic throttle module (ETM) this means that the frozen values will be from a point in time after the diagnostic trouble code (DTC) first occurred.
For certain fault-tracing it is recommended that the ignition is switched off and switched on twice before erasing the diagnostic trouble codes (DTCs). This depends on the diagnostic trouble codes (DTCs) being generated according to the command from the Electronic throttle module (ETM), but as only the Engine control module (ECM) is erased, the Electronic throttle module (ETM) must be switched off completely (powerless) for its memory to be entirely erased. This must be carried out before the vehicle is test driven, otherwise the fault can be recreated in the Engine control module (ECM).
For the Engine control module (ECM) and Electronic throttle module (ETM) to be completely switched off the following must be carried out:
- Ignition off, then wait 3 minutes for the main relay/system relay to release the voltage supply to the Electronic throttle module (ETM) among other things.
- Then switch the ignition on and off again.
- Wait a further 3 minutes. If the engine cooling fan is running, wait a further 2 minutes after the engine cooling fan has stopped, to ensure that the Electronic throttle module (ETM) is switched off correctly.
Reconfigurations
A CAN or the throttle related fault can result in both the Engine control module (ECM) and the Electronic throttle module (ETM) switching to the reconfiguration mode (limp home). This mode is maintained for the rest of the operating cycle in which the fault occurred and in all following cycles where the fault is still present.
Depending on the detected type of fault, the control modules can assume different levels of reconfiguration. Reconfiguration covers everything from preventing cruise control being used due to a temporary break in communication with the cruise control switch, to the Electronic throttle module (ETM) using a fixed throttle angle and the Engine control module (ECM) controlling the engine speed with the ignition and fuel injection.
In the last named reconfiguration, the engine's idle speed may seem uneven because the Engine control module (ECM) for controlling the speed, closes the fuel supply to the cylinders individually. This reconfiguration (engine's behavior) must not be confused with an actual problem in driveablity, which occurred before the reconfiguration.
For example, a short break in the voltage supply to the Electronic throttle module (ETM) means that the control module is reconfiguring itself. Be aware that the engine's behavior then depends on a fault being detected and that the fault is detected because of this behavior.
Note! Upgraded software for the Engine control module (ECM) and Electronic throttle module (ETM) available during 2006 or later, has other conditions for determining when the reconfiguration must occur. The throttle system with this software is more tolerant of faults, which means that the reconfiguration in some cases occurs at other occasions.

The following reconfigurations (limp home) occur:
- Fuel shut-off that follows the accelerator pedal position.The engine's speed is controlled via fuel shut-off by the injector valves switching off one at a time. The engine's speed is determined by the position of the accelerator pedal sensor and the speed is maximized to approximately 5000 rpm. This reconfiguration can make engine idling seem to be uneven because the Engine control module (ECM) for controlling the engine's speed, closes the fuel supply to the cylinders individually. This reconfiguration (engine's behavior) must not be confused with an actual problem in driveablity, which occurred before the reconfiguration.
- Slower throttle opening than the requested throttle opening.The throttle opens more slowly than normal requested opening because the system is only regulated by the pulse width modulated signals from the accelerator pedal position sensor. The driver may notice that the engine responds slightly slower than at normal acceleration.
- Throttle closure when braking.The accelerator pedal position is ignored when the brake pedal is depressed.
- The throttle follows the accelerator pedal position. The throttle and accelerator pedal are used as if they were mechanically connected to each other. This reconfiguration is always determined by fuel-shut off as above.
- Throttle closed. The Electronic throttle module (ETM) switches off the throttle motor's control, which means that the throttle is not affected and therefore returns to the mechanical stop position. This means approximately 20 % throttle opening. This reconfiguration is always determined by fuel shut-off as above.
- Cruise control off.The cruise control is off during the operating cycle when the fault was detected. The function is available at next start-up if the fault is no longer present.