P0123: Throttle - Pedal Position Sensor - Switch A Circuit High Input

What P0123 tells you, and what it does not

The computer reads a voltage from the throttle position sensor circuit higher than any plausible throttle angle, which usually points to a short to power, a failed sensor, or a wiring fault.

The code sits in the throttle position sensor circuit area and is reported by the comprehensive component monitor. It names the circuit or the condition where the computer saw a reading outside its expected range. It does not name a failed part, and several genuinely different faults set this same code, which is the whole reason the causes below are ordered rather than listed.

What people usually notice

• Reduced power or limp mode
• Unexpected surges in idle speed
• Check engine light
• Hesitation on acceleration

What causes P0123?

The causes below are ordered by how often they turn out to be the answer, cheapest and most common first. That order matters more than the list itself: the expensive component named in the code text is very rarely the first thing to replace, and working down from the top is what stops a throttle position sensor circuit fault becoming an expensive guess.

Sensor signal wire shorted to a power circuit is the one to rule out before anything else. Common after aftermarket wiring work near the throttle body.

Working out which cause it is

Start with freeze frame. Throttle position at the fault shows how implausibly high the reading was relative to actual pedal input. That snapshot is taken at the instant the code set, and it is the single most useful piece of evidence you have, which is also why clearing the code before reading it is such a costly habit.

This code is diagnosed by watching values change rather than by reading the number again, so the tool has to stream live data and hold freeze frame. Live sensor voltage readings while working the throttle show whether the signal is pinned near its maximum regardless of actual pedal position.

The order worth working in

• 1. Sensor signal wire shorted to a power circuit: Common after aftermarket wiring work near the throttle body.
• 2. Failed sensor sending a falsely high signal: Internal sensor damage can push the output past its normal range.
• 3. Damaged or corroded connector causing an internal short: Moisture intrusion can bridge pins that should be separate.

What P0123 means for driving the car

Many vehicles will limit power as a safety measure, so limit driving until this is checked.

This is a severity 3 of 4 code, which means continuing to drive normally risks damage that costs considerably more than the repair in front of you. Treat the lamp as an instruction rather than a notification.

What does it cost to ignore P0123?

A stuck high throttle signal can force a persistent limp mode, and continued driving in that condition means unpredictable and reduced power.

There is also the diagnostic cost of waiting. Freeze frame data, pending code history and the readiness monitor state all describe the fault as it was when it set, and all of it is lost the moment somebody clears the code to make the lamp go out.