P0123
Throttle Position Sensor/Switch A Circuit High InputP0123 is a generic OBD-II powertrain diagnostic trouble code: Throttle Position Sensor/Switch A Circuit High Input. It is logged by the engine control unit when the throttle monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0123 means
P0123 is a generic OBD-II powertrain code meaning the PCM or ECM has detected that the voltage signal from Throttle Position Sensor (TPS) circuit A is continuously above the manufacturer-defined maximum threshold — typically above 4.5 V for more than approximately two seconds. Under normal operation, the TPS signal voltage rises proportionally with throttle opening from around 0.5 V (closed) to 4.5 V (wide open); a reading above this ceiling tells the ECM the sensor or its circuit has a fault.
On drive-by-wire (electronic throttle control) vehicles the ECM cross-references TPS A against TPS B at all times. A high-voltage fault on circuit A — whether caused by a failed sensor, a short to a voltage source, or a broken ground wire — will immediately trigger P0123 and often cause the ECM to activate a reduced-power or fail-safe mode to prevent uncontrolled acceleration.
Common companion codes include P0120 (general circuit malfunction), P0121 (range/performance), and P0122 (circuit low). If P0123 appears alone it most often points to a shorted signal wire or a failed TPS. If P0123 appears together with P0122 on the opposite sensor, the throttle body assembly itself is likely faulty.
Severity is high because an ECM receiving a falsely high throttle signal may mismanage fuelling or leave the driver with reduced or unpredictable throttle authority. The vehicle should be diagnosed promptly; do not attempt sustained highway driving with this code active.
Common causes
Most-frequently reported root causes when P0123 is logged.
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1
Faulty throttle position sensor sending signal voltage above 4.5 V
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2
Short circuit in the TPS signal wire to a higher voltage source
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3
Open or high-resistance ground wire in the TPS circuit
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4
Corroded or spread connector pins causing resistance in the reference circuit
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5
Carbon buildup causing the throttle plate to bind in a partially open position
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6
Damaged or water-ingressed TPS connector
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7
Faulty accelerator pedal position sensor (drive-by-wire vehicles)
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8
Failed electronic throttle body assembly
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9
PCM/ECM fault (rare, diagnose last)
Symptoms drivers notice
How to diagnose P0123
A typical diagnostic flow when this code is present.
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1
Scan for all stored DTCs and record freeze-frame data; note any companion TPS codes (P0120–P0122) that help isolate the fault.
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2
Visually inspect the TPS wiring harness and connector for abrasion, melted insulation, corrosion, or pins pushed back in the housing.
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3
With ignition ON (engine off), back-probe the TPS signal wire and measure voltage; a healthy sensor reads ~0.5 V at rest and increases to ~4.5 V at wide-open throttle. A reading above 4.8 V at rest confirms the high-input condition.
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4
Check the TPS 5 V reference supply and ground circuit continuity with a multimeter; an open ground can force the signal line high.
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5
Monitor TPS A and TPS B voltages on a live scan while slowly opening the throttle — both should track smoothly and proportionally.
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6
Wiggle the connector and harness while watching live data to detect intermittent shorts.
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7
If wiring checks pass, replace the TPS sensor (or throttle body assembly on integral-sensor units) and retest.
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8
Clear codes and verify repair with a complete drive cycle.
Vehicles where we've handled P0123
Platforms in our catalogue with confirmed P0123 coverage.
Related powertrain codes
- P0120 — Throttle Position Sensor/Switch A Circuit Malfunction
- P0121 — Throttle Position Sensor/Switch A Circuit Range/Performance Problem
- P0122 — Throttle Position Sensor/Switch A Circuit Low Input
- P0124 — Throttle Position Sensor/Switch A Circuit Intermittent
- P0220 — Throttle/Pedal Position Sensor/Switch B Circuit Malfunction
- P0221 — Throttle/Pedal Position Sensor/Switch B Circuit Range/Performance
Frequently asked questions
Can a dirty throttle body cause P0123?
Yes, indirectly. Severe carbon buildup can prevent the throttle plate from fully closing, keeping the sensor near its maximum range and triggering the high-input threshold. Cleaning the throttle body is a worthwhile early step.
Is P0123 dangerous to drive with?
It is considered a high-severity code. The ECM may restrict throttle response or enter limp mode, making highway merging or overtaking hazardous. Diagnosis should not be delayed.
What is the difference between P0122 and P0123?
P0122 means the TPS signal voltage is below the minimum threshold (circuit low), while P0123 means it is above the maximum threshold (circuit high). Both indicate a circuit fault but point to opposite failure modes — low often means a short to ground or broken signal wire, high often means a short to voltage or an open ground.
Will clearing the code make it go away permanently?
Only if the root cause has been repaired. If the sensor or wiring fault is still present, the code will return within the same drive cycle or the next one.
Do I need to calibrate or relearn the TPS after replacement?
Many modern vehicles with electronic throttle control require a throttle body relearn procedure after replacement. Consult the vehicle's service documentation; failure to relearn can cause idle quality issues even with a correctly fitted sensor.
Disabling P0123 in software
RaceTune can permanently disable P0123 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
ECUs with a P0123 disable in our catalogue
Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.
- Bosch EDC17C50 verified 1 software version
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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