P2104: Throttle Actuator Control System — Forced Idle
Do not keep driving
The car will run but barely move, and that restriction is protecting you rather than failing. Ask what other codes are stored — this one records the response, and another names the actual fault. If a workshop quotes for a throttle body on the strength of this code alone, they have not finished reading the vehicle. Have it recovered rather than driven in traffic.
What this code means
The module has forced the throttle to idle. This is not a fault — it is the response to one, and reading it as a fault sends the diagnosis to the wrong place.
Drive-by-wire has no mechanical link between pedal and throttle, so it is built to distrust itself. Every safety-critical signal is duplicated: two or three independent accelerator pedal sensors, two throttle position sensors, deliberately given different characteristics — one rising while the other falls, or running at different slopes — so that a single fault cannot produce two plausible readings that agree. When the module finds a disagreement it cannot resolve, it does not guess. It withdraws authority.
That withdrawal is graded, and the four codes describing it are worth reading together:
- P2104 — forced idle. Throttle held closed; engine runs, vehicle barely moves.
- P2110 — forced limited RPM. A revolution ceiling, enough to drive slowly.
- P2106 — forced limited power. A torque ceiling rather than a rev ceiling.
- P2105 — forced engine shutdown. The most severe, and the engine stops.
Which one appears tells you how badly the module has lost confidence, and none of them tells you why. The cause is a separate code stored alongside — a pedal sensor correlation fault, a throttle position disagreement, a motor circuit problem. Diagnosing P2104 on its own terms means investigating a symptom while the cause sits in the same list.
The most common underlying causes are cheap: a corroded pedal sensor connector, carbon around the throttle plate, or a failing reference voltage feeding both sensors of a pair at once.
Likely causes
Start here
- Fault in the accelerator pedal position sensors · moderate
- Fault in the throttle position sensors · moderate
- Corroded or loose connector · easy
- Carbon deposits in the throttle body · easy
Less common
- Failed sensor reference voltage supply · moderate
- Faulty throttle actuator motor · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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