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 driveability. 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).

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 driveability, 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.

For information about how to identify the software in the control module, see: Identifying upgraded software ECM/ETM

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 driveability, 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.