P0122 – Throttle/Pedal Position Sensor/Switch A Circuit Low Input

What does P0122 mean?

The throttle position sensor (TPS) circuit is reporting a voltage lower than the valid range. The TPS tells the computer how far the throttle is open; on drive-by-wire vehicles this sensor is part of the throttle body assembly and is critical to how the engine responds to your foot.

What causes P0122?

Listed from most to least common:

1. 1Failed throttle position sensor
2. 2Short to ground in the TPS signal wire
3. 3Damaged or corroded connector
4. 4Loss of 5V reference voltage from the computer
5. 5Worn throttle body on high-mileage vehicles

Code breakdown

Common symptoms

• Check engine light on
• Reduced power / limp mode
• Hesitation or surging on acceleration
• Erratic or unstable idle
• Poor or delayed throttle response
• Transmission shifting problems on some vehicles

How to diagnose

1. 1Check the TPS connector for damage, corrosion, or a loose fit.
2. 2Verify the 5V reference is present at the sensor with the key on.
3. 3Inspect the signal wire for shorts to ground.
4. 4Watch live TPS data while slowly opening the throttle — the value should rise smoothly with no dropouts or dead spots.
5. 5On drive-by-wire systems, check both throttle position signals, as they should track each other consistently.

This can cause unpredictable throttle response or force the vehicle into reduced-power limp mode. Treat unexpected throttle behavior as a safety issue.

Common fixes and estimated costs

Costs are rough US estimates including parts and labor. Actual pricing varies significantly by vehicle, region, and shop rates.

Good to know

After replacing a TPS or throttle body, most vehicles require an idle relearn or throttle position calibration. Skipping it commonly causes idle problems and a returning code.

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