P2104
Throttle Actuator Control System — Forced Idle
The ECU has detected a fault severe enough that it forces the throttle actuator to the idle stop. The driver loses pedal authority — only idle is available until the underlying TAC fault clears.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
Symptoms
- Check engine light on
- Reduced throttle response, possible limp mode
- Hesitation or surging
- Idle too high or too low
Common causes
Ordered by how often each turns out to be the cause.
- Severe upstream TAC faultCommon
- Throttle position signal invalidPossible
Parts involved
- Throttle Actuator Control
- ECM
P2104 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.