OBD-II trouble code
P2104: Throttle Actuator Control System - Forced Idle
The engine control module has locked the engine to idle as a protective response to a throttle control fault. The engine runs but will not accelerate past a fixed low speed. This is a fail-safe declaration, not a broken part — the real fault is in a companion throttle or pedal code.
Quick facts
- System
- Powertrain
- Category
- Fuel & Air Metering
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $0 – $900
- DIY difficulty
- Intermediate DIY
What does P2104 mean?
On a drive-by-wire vehicle there is no cable between the accelerator pedal and the throttle plate. The pedal contains two position sensors, the throttle body contains a motor and two more position sensors, and the engine control module sits in the middle deciding how far to open the throttle. That arrangement is only safe if the module can trust every one of those signals. Redundant sensors exist precisely so the module can cross-check them, and when the cross-check fails it has to assume the worst — an unintended-acceleration scenario — and take control away.
P2104 is the module announcing that it has done exactly that, at the middle tier of severity. It has forced the throttle to a fixed idle position and will not open it further regardless of what the pedal says. The engine still runs and the vehicle may creep, but it will not accelerate. This sits between P2110, which caps engine speed at a reduced but still usable limit, and P2105, which shuts the engine down entirely. Which tier the module chooses depends on how badly it distrusts the throttle system.
The key thing to understand is that P2104 is a consequence, not a cause. It is the response to another fault, and it will almost always be stored alongside the code that actually identifies the problem — a throttle actuator motor circuit code such as P2100, P2102, or P2103, a throttle position sensor code such as P0122 or P0123, a throttle position correlation code such as P2135, or an accelerator pedal position code such as P2138. Clearing P2104 without repairing the companion fault accomplishes nothing; the module will force idle again within seconds of the next drive cycle.
Beyond sensor and wiring faults, two mundane causes deserve attention. Heavy carbon buildup in the throttle bore can physically prevent the plate from reaching its commanded position, which the module reads as an actuator that is not obeying and treats as a control failure. And low system voltage from a weak battery or a failing alternator can make the throttle motor sluggish enough that commanded and actual position disagree, producing a throttle fault that has nothing to do with the throttle body at all. Both are worth ruling out before ordering parts.
Common causes
- Companion throttle actuator control fault (P2100, P2101, P2102, P2103) driving the fail-safe
- Heavy carbon buildup binding the throttle plate so it cannot reach commanded position
- Failed throttle actuator control motor inside the throttle body
- Faulty throttle position sensor or a correlation failure between the two throttle sensors
- Faulty accelerator pedal position sensor or pedal sensor correlation failure
- Chafed, corroded, or broken wiring in the throttle or pedal circuits
- Corroded or loose connector at the throttle body or pedal assembly
- Low system voltage from a weak battery, bad connection, or failing alternator
- Poor engine or module ground affecting sensor reference voltages
- Aftermarket alarm, remote start, or accessory wiring spliced into throttle or pedal circuits
- Failed engine control module (rare — verify wiring, grounds, and voltage first)
Symptoms
- Engine runs but will not accelerate past idle
- Check engine light on, usually with a reduced-power or wrench warning as well
- Pedal feels completely unresponsive
- Vehicle creeps in gear but cannot be driven at road speed
- Rough or unstable idle in some cases
- Companion throttle or pedal codes stored alongside P2104
- Symptom may clear after a key cycle and return during the next drive
Diagnostic steps
- 1.Scan and record every stored and pending code from all modules. P2104 is a fail-safe, so the companion code is the one that identifies the actual fault — repair that, not this.
- 2.Test the battery and charging system before anything else. Low voltage makes the throttle motor sluggish and produces throttle faults that no amount of parts replacement will fix.
- 3.Inspect the throttle body and accelerator pedal connectors for corrosion, backed-out pins, damaged locks, and pins pushed out of the housing.
- 4.Compare commanded throttle position against actual throttle position in live data while an assistant sweeps the pedal. A commanded value that moves while actual does not confirms the actuator or its circuit.
- 5.View both accelerator pedal position sensor signals together. They should track each other smoothly across the whole travel — a flat spot or a divergence in one of them is the fault.
- 6.View both throttle position sensor signals the same way, looking for dropouts or a signal that sticks at one value.
- 7.Remove the intake ducting and inspect the throttle bore for carbon buildup. Try moving the plate by hand with the key off and the connector unplugged; it should move against spring pressure and snap back cleanly, with no gritty binding.
- 8.Check for aftermarket wiring spliced into the throttle or pedal harness. Remote starts and alarms are a recurring source of exactly this fault.
- 9.Voltage-drop test the engine and module grounds; a poor ground shifts sensor reference voltages and breaks the correlation checks.
- 10.Repair the confirmed fault, perform the manufacturer's throttle relearn procedure, clear codes, and verify with a full drive cycle that normal throttle response returns.
Repair cost
$0 – $900
The low end is zero because a connector left unplugged, a blown fuse, or a battery terminal that needs cleaning are all real fixes with no parts cost. A throttle body cleaning is typically $80-$200. A replacement throttle body commonly runs $250-$700 installed including the relearn procedure, and an accelerator pedal assembly $150-$400. Wiring repair varies with how much harness is affected. Because P2104 tracks whatever the companion code identifies, the honest answer is that the cost is entirely determined by that underlying fault — diagnosis first, parts second.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with throttle body replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.