What it means
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.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
The throttle actuator control system manages the electronic throttle and can limit its movement when another fault makes normal control unsafe. P2104 records that the system has forced the throttle to its idle position, commonly after a serious throttle-control fault or invalid throttle-position feedback.
Common causes
Most likely first.
- Severe upstream TAC fault
- Throttle position signal invalid
Symptoms
- Check engine light on
- Reduced throttle response, possible limp mode
- Hesitation or surging
- Idle too high or too low
How to diagnose it
- Save freeze-frame data and scan for other throttle, pedal, and position-sensor codes, since P2104 often reports the system's response to another fault.
- Check live data for commanded throttle, actual throttle position, and throttle-position signals to see whether feedback is invalid or inconsistent.
- Inspect the throttle body, connector, and harness for a stuck plate, loose plug, corrosion, or damaged wiring.
- Test the throttle-position signals and actuator circuit using the wiring diagram and manufacturer's procedure.
- Diagnose and repair the underlying fault indicated by the other codes, then verify normal throttle response using the approved relearn or test procedure.
Common fixes
- Repair the underlying throttle actuator or position-signal fault identified by companion codes.
- Clean and secure a loose or corroded throttle-body connector, or repair damaged wiring.
- Clean a sticking throttle plate using the manufacturer's approved method.
- Perform the required throttle relearn after the fault is repaired.
Can I keep driving?
With the system forcing idle, the accelerator may not provide useful power; do not continue into traffic or attempt to drive at speed. Move to a safe place if possible and arrange recovery.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.