A faulty throttle position sensor that has worn internally and now outputs a voltage above its normal range; A short to voltage on the sensor signal wire, often from chafed insulation against a nearby power wire; A poor or corroded ground connection at the sensor or engine block, which skews the reference voltage the sensor returns; A damaged or misadjusted sensor connector, including bent pins or a loose terminal that intermittently bridges to voltage; Contamination or mechanical binding inside the throttle body that holds the sensor at an unrealistic angle; A faulty engine computer, which is rare but possible when all wiring and sensor checks pass; Water intrusion into the sensor or connector causing an intermittent high-voltage reading

DTC codes / P01xx · Fuel and air metering / P0123

P0123Throttle Position Sensor A Circuit High Input

Q: What does code P0123 mean?

Throttle Position Sensor A Circuit High Input. P0123 means the engine computer has seen the throttle position sensor's signal voltage go higher than the maximum value it expects for the current operating conditions. The sensor is reporting a throttle angle that is more open than the computer believes is physically possible, so the computer flags the circuit as a high input fault.

P0123 means the engine computer has seen the throttle position sensor's signal voltage go higher than the maximum value it expects for the current operating conditions. The sensor is reporting a throttle angle that is more open than the computer believes is physically possible, so the computer flags the circuit as a high input fault.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

The check engine light is on, and often there are no other symptoms besides the warning light
The engine may idle at an abnormally high speed or surge when coming to a stop
Acceleration may feel flat or delayed because the computer is limiting power based on a false high throttle reading
An automatic transmission may shift harshly or at the wrong points because it uses throttle position for shift scheduling
The vehicle may enter limp mode with reduced engine power or a fixed idle speed
Cruise control may stop working or disengage unexpectedly

Common causes, most likely first

A faulty throttle position sensor that has worn internally and now outputs a voltage above its normal range
A short to voltage on the sensor signal wire, often from chafed insulation against a nearby power wire
A poor or corroded ground connection at the sensor or engine block, which skews the reference voltage the sensor returns
A damaged or misadjusted sensor connector, including bent pins or a loose terminal that intermittently bridges to voltage
Contamination or mechanical binding inside the throttle body that holds the sensor at an unrealistic angle
A faulty engine computer, which is rare but possible when all wiring and sensor checks pass
Water intrusion into the sensor or connector causing an intermittent high-voltage reading

How to diagnose and fix it

Connect a scan tool and read the throttle position sensor voltage live; compare the reading at closed throttle and wide-open throttle against the manufacturer's specification
Visually inspect the sensor connector, pins, and the length of the signal wire for chafing, corrosion, or signs of water intrusion
Back-probe the sensor signal wire and measure voltage with a digital multimeter while slowly opening and closing the throttle by hand
Check the sensor ground circuit for excessive resistance by measuring voltage drop between the sensor ground pin and battery negative
Wiggle-test the harness and connector while watching live data to catch an intermittent short to voltage
If wiring and grounds are good, replace the throttle position sensor and clear the code, then verify the voltage sweep is smooth and within range
After any repair, perform a throttle relearn or idle relearn procedure if the manufacturer requires it, then confirm the code does not return

What a high TPS reading really tells you

A shorted signal wire can mimic a failed sensor perfectly, so always wiggle-test the harness before condemning the sensor itself
A bad ground on the sensor circuit raises the return voltage and sets P0123 even though the sensor is healthy, which is a common misdiagnosis trap
Some vehicles set this code from a throttle body that is carbon-fouled and holding the plate open slightly, so cleaning the bore can resolve it without parts
P0123 can appear alongside transmission codes because the computer uses throttle position for shift strategy, and those codes often clear once the TPS signal is corrected
On drive-by-wire vehicles the throttle position sensor is part of the electronic throttle body, so the repair may involve the whole assembly rather than a standalone sensor

Can I keep driving with P0123?

You can usually drive the vehicle to a shop, but expect reduced power, a high or erratic idle, and harsh shifting. Avoid heavy acceleration and highway merging until the fault is repaired, because limp mode can cut power unexpectedly.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.