P2104 Code: Throttle Actuator Control System – Forced Idle
A fail-safe has locked the engine at idle and the gas pedal no longer works – another code tells you why.
Stop driving
Don't try to drive on: the car only creeps at idle and cannot accelerate out of danger. Coast to the shoulder or a parking spot and arrange a tow; restarting may restore the pedal briefly, but the fault can return at any moment.
At a glance
Severity: High
- Meaning
- Throttle Actuator Control System – Forced Idle
- System
- Speed & Idle Control · Powertrain
- Safe to drive?
- No — stop driving
- Typical repair cost
- $50–$900
- DIY difficulty
- Moderate
P2104 is not a broken part but a decision: the PCM has stopped trusting the driver's request and holds the engine at an elevated idle, typically somewhere around 1,200–1,500 rpm, no matter how far you press the pedal. It does this when it can no longer tell safely what the driver wants – most often because both accelerator pedal position sensors are faulty or disagree, because the brake and pedal signals contradict each other, or because a shared 5-volt sensor supply has collapsed. The real fault is almost always stored as a separate code, such as P2138, P2122–P2128 or a brake switch code. Fix that root code and P2104 goes away with it.
How to read P2104
- P Powertrain
- 2 Generic (SAE)
- 1 Fuel & air metering
- 04 Specific fault
Symptoms
- Gas pedal does nothing – engine stays at a raised idle
- Car creeps slowly in gear and cannot climb hills or merge
- Several warning lights at once: check engine, electronic throttle, sometimes traction control
- Fault may clear after switching off and restarting, then return
- Cruise control inoperative
- Brake lights on constantly or not at all if the brake switch is involved
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Accelerator pedal position sensor failure or disagreement between its two tracks
- Brake switch fault or brake/accelerator plausibility conflict
- Shorted 5-volt reference circuit shared by the pedal and throttle sensors
- Throttle position sensor correlation fault inside the throttle body
- Corroded or damaged connector and wiring at the pedal assembly
- PCM software or internal fault
Diagnosis step by step
Find the root code
Read codes from the PCM and, if your scanner allows, the ABS and body modules too. P2104 almost never stands alone; the companion code – pedal, throttle, brake switch or sensor supply – tells you where to start.
Tools: OBD-II scanner
Test the pedal signals
With the key on and engine off, graph accelerator pedal position D and E (generic PIDs 49 and 4A). Both must rise smoothly and without dropouts as you press slowly; on many designs the second track reads about half of the first. A step, spike or flat spot condemns the pedal or its wiring.
Tools: OBD-II scanner
Check the brake switch
Watch the brake switch status in live data and have someone check the brake lights. The status must change cleanly with a light press and return when released; a switch that is misadjusted, sticking or reports both states at once can force idle for safety.
Tools: OBD-II scanner, Flashlight
Measure the 5-volt references
Back-probe the reference pins at the pedal and throttle body with the key on; expect roughly 4.9–5.1 V. If a reference is low, unplug the sensors on that circuit one at a time – the one whose removal restores 5 V is shorted internally.
Tools: Multimeter
Inspect pedal connector and harness
The pedal connector sits low in the footwell where wet shoes and spilled drinks reach it. Look for corrosion, a cracked latch and wires pinched by the floor mat or pedal bracket.
Tools: Flashlight
Clear codes and road test
After the repair, clear all codes, cycle the key and test pedal response in a safe place before driving in traffic. Make sure the pedal tracks, brake status and throttle response all agree during a test drive with gentle and firm acceleration.
Tools: OBD-II scanner
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace accelerator pedal sensor/pedal assembly | Yes | $150–$450 |
| Replace or adjust brake light switch | Yes | $50–$150 |
| Repair shorted 5 V reference or pedal wiring | No | $120–$450 |
| Replace electronic throttle body | No | $350–$900 |
| Tow and diagnostic time | No | $150–$350 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Field data
| Ford | 13 | Fusion, 500, Freestyle |
|---|
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
The root fault behind P2104 lights the check engine light, so an OBD emissions or smog test fails. In practice the car can't be driven to the test until the pedal or throttle problem is repaired.
Frequently asked questions
Why does the car only idle even when I floor the pedal?
The PCM has decided it cannot trust the pedal signal, so it ignores it completely and holds a safe idle. That protects against sudden unwanted acceleration if the sensor is sending false readings.
Can a bad brake light switch cause forced idle?
Yes. Many engines cut the throttle when the brake is pressed; if the switch reports braking and not braking at the same time, or the brake signal disagrees with the pedal, the PCM may lock the engine at idle.
The pedal worked again after a restart – am I fine?
No. The restart simply cleared the fail-safe until the next time the fault is seen. Have the root code diagnosed before relying on the car, because it can happen again in traffic.
Could a floor mat have triggered P2104?
Indirectly. A mat pressing on the gas pedal while you brake can trigger the brake-override logic and store related codes. Remove loose or stacked mats and make sure the pedal returns fully.