P2104

Actuator Control System - Forced Idle

P2104 is a generic OBD-II powertrain diagnostic trouble code: Actuator Control System - Forced Idle. 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
P2104
Group
Powertrain
System
SCR/AdBlue
Severity
Critical (limp mode / no-start)
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What P2104 means

P2104 is set when the powertrain control module (PCM) commands the electronic throttle control (ETC) system into a forced idle state as a protective response to a detected fault in the throttle actuator control system. The PCM overrides normal driver demand and clamps engine speed to idle to prevent uncontrolled acceleration.

This code is almost always a secondary or companion code accompanying a root-cause fault such as a throttle position sensor disagreement, accelerator pedal position sensor fault, or ETC motor failure. The forced idle strategy is a failsafe, not an independent failure mode. The engine will typically run but will not respond to throttle input.

Diagnosing P2104 requires identifying and resolving the primary fault code first. Clearing P2104 alone without addressing the underlying cause will result in immediate or rapid re-set. Common root faults include APP sensor circuit issues, TP sensor signal faults, and ETC relay or power supply problems.

Common causes

Most-frequently reported root causes when P2104 is logged.

  • 1
    Primary ETC fault code present (e.g. P0120, P0220, P2135) triggering the forced idle strategy.
  • 2
    Throttle position sensor signal disagreement between TP1 and TP2.
  • 3
    Accelerator pedal position sensor malfunction or out-of-range signal.
  • 4
    ETC throttle body motor circuit open, short, or high resistance.
  • 5
    PCM internal fault or software error affecting ETC control module.
  • 6
    Loss of ETC relay power or ground supply.
  • 7
    Wiring harness damage, corrosion, or connector failure in the ETC circuit.

Symptoms drivers notice

Engine stuck at idle with no throttle response.
MIL illuminated, often with multiple related ETC codes stored.
Vehicle enters limp-home mode immediately.
Traction control or stability control warning lights may also illuminate.
Normal engine start possible but acceleration completely disabled.

How to diagnose P2104

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and record all stored and pending DTCs before clearing anything.
  2. 2
    Identify and prioritize any primary ETC fault codes stored alongside P2104.
  3. 3
    Check live data for TP1, TP2, APP1, and APP2 sensor values at rest and with pedal input.
  4. 4
    Inspect ETC throttle body wiring harness and connectors for damage, corrosion, or loose pins.
  5. 5
    Verify ETC relay operation and supply voltage to the throttle actuator.
  6. 6
    Test ETC motor resistance and compare to specification if wiring checks pass.
  7. 7
    Address all primary fault codes first, then retest to confirm P2104 does not re-set.

Related powertrain codes

Frequently asked questions

Can I drive with a P2104 code?

The vehicle will typically only idle and will not respond to throttle input, making it unsafe and impractical to drive beyond moving it to a safe location.

Will clearing the code fix the problem?

No. P2104 is a failsafe response to another fault. It will re-set immediately unless the root-cause code is identified and repaired.

Does P2104 always mean the throttle body needs replacing?

Not necessarily. The forced idle command is often triggered by sensor or wiring faults rather than a failed throttle body motor. Full circuit diagnosis is required first.

Why are there multiple codes alongside P2104?

The ETC system uses redundant sensors and the PCM cross-checks them continuously. A single component failure typically triggers several related codes plus the forced idle code.

Disabling P2104 in software

RaceTune can permanently disable P2104 — 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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