OBD Code P0122: Throttle Position Sensor/Switch A Circuit Low Input

Q: What does OBD code P0122 mean?

Throttle Position Sensor/Switch A Circuit Low Input. Your throttle position sensor is sending a voltage signal that's too low, like a dimmer switch stuck in the off position. The engine computer can't properly gauge how much the driver is pressing the gas pedal.

Q: What are the symptoms of fault code P0122?

Engine hesitation or lack of power during acceleration, Check Engine Light illuminated, Rough idle or stalling

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What This Actually Means

In plain language — no jargon

Your throttle position sensor is sending a voltage signal that's too low, like a dimmer switch stuck in the off position. The engine computer can't properly gauge how much the driver is pressing the gas pedal.

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Symptoms You May Notice

3 known symptoms for this code

Engine hesitation or lack of power during acceleration

Check Engine Light illuminated

Rough idle or stalling

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Embedded Systems Insight

What the ECU/ECM is actually computing

The ECU monitors the throttle position sensor's analog voltage output, which normally ranges from 0.5V (closed throttle) to 4.5V (wide open throttle). When the signal drops below the expected minimum threshold at idle, the ECU logs a fault and cannot accurately calculate fuel injection and ignition timing.

Voltage & Parameter Thresholds

Parameter	Normal Range	Fault Condition
TPS Voltage at Idle	0.5V – 1.0V	Below 0.5V
TPS Voltage WOT	4.0V – 4.8V	Below 3.5V under load

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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex

1

Throttle Position Sensor Connector

Inspect and clean the TPS connector pins for corrosion or loose contacts; reseat firmly.

2

Engine Wiring Harness

Check the TPS circuit wiring for breaks, pinches, or corrosion between the sensor and ECU.

3

Throttle Position Sensor

Replace the TPS unit if connector and wiring are intact and voltage remains low.