|Code||Fault Location||Probable Cause|
|P2108|| Throttle actuator control (TAC) module - performance problem |
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|TAC control module|
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What Does Code P2108 Mean?
OBD II fault code P2108 is a generic code that is defined as “Throttle Actuator Control Module Performance”, and is set when the PCM (Powertrain Control Module) detects an abnormal or unexpected output signal from the throttle actuator control module. Note that this code only applies to applications that use drive-by-wire throttle control systems in which there is no physical link such as a control cable between the throttle pedal and the throttle plate.
Drive-by-wire throttle control systems are fairly complex systems that use input data from the throttle position sensor to activate a DC motor to control the opening and closing of the throttle plate. In practice, the reference voltage that is supplied to the throttle pedal position sensor changes depending on the position of the sensor, and the PCM uses these changes and input data from other engine sensors to calculate an appropriate throttle opening, which is monitored by a dedicated throttle plate position sensor.
As a practical matter, when the engine is running and the throttle pedal is in the rest position, the PCM will open the throttle plate just enough to allow stable idling. As the throttle pedal is depressed, the current from the pedal position sensor changes and the PCM uses this information to command the throttle actuator motor to create a bigger throttle opening via the throttle control module, which it will maintain unless the driver presses down further on the throttle pedal. If the driver removes all pressure from the throttle pedal, the voltage from this sensor changes again, but in the opposite direction, which has the effect of closing the throttle (via the throttle control module and throttle control motor) to a minimum opening to maintain the engines’ idling speed.
It should be noted though the PCM monitors several parameters continuously during throttle/engine operation. These include, but are not limited to the correlation between the actual and desired positions of the throttle plate and the throttle pedal position sensor, the correlation between the engine speed and the actual throttle opening, and all voltages and currents in the throttle control system, with special reference to the output signals from the throttle control module.
Thus, if the PCM detects a malfunction such as an incorrect, implausible, inaccurate, or unexpected signal from the throttle control module that produces an actual throttle position that does not agree with the desired throttle position, it recognizes that it cannot control the throttle effectively, and it will set code P2108 and illuminate a warning light as a result. Note that on many applications, this type of failure may cause the PCM to initiate a fail-safe or limp mode as a safety precaution, and that the fail-safe condition will persist until the fault is corrected and the code is cleared with a scan tool.
Where is the P2108 sensor located?
The image above shows a simplified schematic drawing of a typical electronic drive-by-wire throttle control system. Note that while in this example the throttle control module is shown as a stand-alone control module, this module can also be integrated into the PCM. Note also that where the throttle control module is a stand-alone unit, the actual locations of these units vary greatly between applications, so refer to the manual for the affected application to locate and identify the throttle control module correctly to avoid a misdiagnosis.
What are the common causes of code P2108?
Some common causes of code P2108 could include the following-
- Damaged, burnt, shorted, disconnected, or corroded wiring and or connectors in one or more throttle control circuits. Note that poor electrical connections in these circuits is a common cause of code P2108 on many applications
- Defective throttle control module
- Defective throttle control system relay
- Defective throttle actuator motor
- Defective throttle position sensor
- Defective throttle pedal position sensor
- Failed or failing PCM, but note that since this a rare event, the fault must be sought elsewhere before any control module is replaced