P2108

Actuator Control Module Performance

P2108 is a generic OBD-II powertrain diagnostic trouble code: Actuator Control Module Performance. It is logged by the engine control unit when the scr/adblue monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P2108
Group
Powertrain
System
SCR/AdBlue
Severity
Warning (MIL on, possible limp mode)
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What P2108 means

P2108 indicates that the PCM has detected a performance problem within the throttle actuator control (TAC) module itself. Unlike codes that flag individual sensor circuits, P2108 points to the control module's ability to accurately command and achieve the desired throttle position. The module may be receiving valid inputs but failing to translate them into correct throttle plate movement.

This fault can arise from an internal TAC module failure, a degraded ETC motor that cannot follow commanded positions within tolerance, or communication errors between the TAC module and the main PCM on systems where these are separate units. On integrated PCM/TAC designs, it may indicate an internal PCM fault affecting the ETC driver circuits.

Because P2108 reflects overall system performance rather than a single circuit, diagnosis involves verifying that all input signals (TP sensors, APP sensors) are accurate and then checking whether the throttle body moves correctly in response to commanded positions. A throttle body relearn procedure is often required after repairs.

Common causes

Most-frequently reported root causes when P2108 is logged.

  • 1
    Internal TAC module failure or degraded ETC driver circuitry.
  • 2
    ETC throttle body motor worn or unable to reach commanded positions.
  • 3
    TP sensor feedback disagreement preventing closed-loop position control.
  • 4
    Communication fault between a standalone TAC module and the PCM.
  • 5
    Intermittent power or ground supply to the TAC module.
  • 6
    Carbon buildup on throttle bore causing mechanical binding.
  • 7
    PCM software or calibration issue affecting ETC control logic.

Symptoms drivers notice

MIL illuminated with possible limp-home or reduced power mode.
Hesitation or stumble during acceleration.
Unstable or erratic idle speed.
Throttle plate response sluggish or inconsistent.
Multiple ETC-related codes may be stored simultaneously.

How to diagnose P2108

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs with a scan tool and note any companion ETC or sensor codes.
  2. 2
    Check live data for TP sensor actual vs. commanded throttle position during controlled input.
  3. 3
    Inspect throttle body for carbon deposits and clean if necessary, then perform a throttle body relearn.
  4. 4
    Verify TAC module power supply and ground integrity with a wiring diagram.
  5. 5
    Check for communication bus errors between TAC module and PCM if the system uses separate modules.
  6. 6
    Test ETC motor response by commanding throttle sweeps with a scan tool if the function is available.
  7. 7
    Replace throttle body assembly or PCM only after all wiring, mechanical, and sensor checks are complete.

Related powertrain codes

Frequently asked questions

Is P2108 the same as a throttle body failure?

Not always. The code points to TAC module performance, which can include the module itself, the motor, mechanical binding, or control circuit issues. Full diagnosis is needed before replacing parts.

Can a throttle body cleaning fix P2108?

If mechanical binding due to carbon buildup is preventing the motor from hitting commanded positions, cleaning followed by a relearn may resolve it. However, electrical or module faults require further diagnosis.

Do I need a relearn after fixing P2108?

Yes. Any time the throttle body is cleaned, removed, or replaced, a throttle body relearn or idle relearn procedure is required to re-establish the ECM baseline throttle position.

Can this code cause a no-start?

P2108 itself typically results in limp mode rather than a no-start, but if the TAC module fails completely the PCM may command forced idle or disable the engine as a safety measure.

Disabling P2108 in software

RaceTune can permanently disable P2108 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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