OBD Code P0123: Throttle Position Sensor/Switch A Circuit High Input

Q: What does OBD code P0123 mean?

Throttle Position Sensor/Switch A Circuit High Input. The throttle position sensor is sending a signal that's too high, like a volume knob stuck at maximum. The engine computer thinks the throttle is wide open when it actually isn't.

Q: What are the symptoms of fault code P0123?

Check Engine Light illuminated, Engine hesitation or surging at idle, Poor fuel economy

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What This Actually Means

In plain language — no jargon

The throttle position sensor is sending a signal that's too high, like a volume knob stuck at maximum. The engine computer thinks the throttle is wide open when it actually isn't.

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Symptoms You May Notice

3 known symptoms for this code

Check Engine Light illuminated

Engine hesitation or surging at idle

Poor fuel economy

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Embedded Systems Insight

What the ECU/ECM is actually computing

The ECU monitors voltage from the Throttle Position Sensor (TPS) to determine throttle opening angle. The sensor typically outputs 0.5–4.5V as the throttle moves from closed to open. A high input means the voltage exceeds the maximum expected threshold, indicating either a sensor malfunction or wiring issue.

Voltage & Parameter Thresholds

Parameter	Normal Range	Fault Condition
TPS Voltage	0.5V–4.5V (closed to wide open)	>4.5V or exceeds max calibrated voltage
Throttle Angle	0–100%	>100% or implausible high reading

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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex

1

TPS connector and wiring

Inspect the connector for corrosion, loose pins, or damaged insulation; reseat or clean contacts.

2

Throttle Position Sensor

Remove and replace the TPS unit if voltage remains high after cleaning connectors.

3

Throttle body and linkage

Check for mechanical binding or debris preventing normal throttle return and operation.