OBD-II Code · Fuel & Air
P2104
Throttle Actuator Control System — Forced Idle
Severity
high
Left alone, this one tends to take other parts with it.
Can you drive it
Not for long
Driving on this one risks further damage. Get it to a shop rather than carrying on with it.
Indicative cost (USD)
$50–$700
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
TAC system forced into idle mode by ECM due to a related fault.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Pedal does nothing
- Engine idles only
- Check engine light
- Limp mode
Likely causes
- Companion TAC fault (P2101/P2118/P2135)Most common
- Backed-out pedal-sensor pin
- Worn pedal sensor
- APP/TPS correlation break
Read the full diagnostic procedureP2104 means the ECM has commanded the throttle into forced-idle mode because it detected a fault somewhere in the TAC system serious enough that it d…
P2104 means the ECM has commanded the throttle into forced-idle mode because it detected a fault somewhere in the TAC system serious enough that it doesn't trust the driver's pedal input anymore. The car will start and idle, but stepping on the gas does nothing — the blade stays at its idle stop and the ECM ignores the pedal sensors entirely. This is almost never the primary fault; P2104 is a consequence code that rides along with whatever actually triggered limp mode (P2101, P2118, P2135, P0120-series, etc.). Pull all stored codes before you touch anything — the companion code tells you which subsystem the ECM doesn't trust.
Cheapest-first
- read the freeze-frame data on the companion code to see what the engine was doing when limp engaged, then run the throttle-body clean if you haven't recently.
- Backprobe TPS-A and TPS-B at the throttle body and APP-D and APP-E at the pedal — all four sensors have to agree within their correlation window or the ECM defaults to forced idle.
- A single backed-out pedal-sensor pin (super common on GM trucks where the pedal harness runs under carpet and gets stepped on) will pop P2104 along with P2135.
Vehicle-specific patterns2007-2014 GM full-size trucks (Silverado / Sierra / Tahoe / Yukon) with the 5.3L / 6.0L is the dominant P2104 platform — corrosion in the accelerator…
- 2007-2014GM full-size trucks (Silverado / Sierra / Tahoe / Yukon) with the 5.3L / 6.0L is the dominant P2104 platform — corrosion in the accelerator-pedal-position (APP) harness connector causes intermittent voltage drops on the pedal sensors and the ECM forces idle within seconds; the fix is repinning or replacing the pedal-sensor pigtail and reseating the connector with dielectric grease.
- 2005-2009Subaru Legacy / Outback / Forester with the EJ25 throws P2104 from internal cracking of the throttle body's plastic gear-train where the motor connects to the blade shaft; replacement throttle body required.
- 2008-2012Honda Accord / Pilot / Odyssey J35 sees P2104 with P2122 / P2127 from a worn pedal-position sensor where the wiper element flat-spots at the rest position. Never clear P2104 without verifying the companion code is also resolved — clearing it alone will let the car drive for 30 seconds before the underlying fault re-asserts and forces idle again, which is dangerous if you're pulling out into traffic.
Look up another code
P2104 — frequently asked
What does a P2104 code mean?
TAC system forced into idle mode by ECM due to a related fault.
What causes a P2104 code?
Common causes: Companion TAC fault (P2101/P2118/P2135); Backed-out pedal-sensor pin; Worn pedal sensor; APP/TPS correlation break.
What are the symptoms of a P2104 code?
Typical symptoms: Pedal does nothing; Engine idles only; Check engine light; Limp mode.
Is it safe to drive with a P2104 code?
Not for long. Driving on this one risks further damage. Get it to a shop rather than carrying on with it. Estimated repair: $50-$700.
How do I diagnose a P2104 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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