P0120 to P0229: throttle and pedal position sensors

What does P0120 mean?

On a modern car the accelerator pedal is not connected to the throttle by a cable. Sensors on the pedal and on the throttle body tell the engine computer where each one is, usually in pairs so each can check the other. When one of them reports a voltage out of range or erratic, the computer cannot be sure what the driver is asking for, and most cars limit power or hold the engine near idle as a precaution.

What causes P0120?

1. A worn sensor track, which gives erratic readings at certain pedal positions
2. A loose or corroded connector at the throttle body or the pedal
3. Damaged wiring, often where the harness flexes
4. A failed sensor reference voltage feeding several sensors at once
5. Water or dirt inside the throttle body connector

What to check first for P0120

• Note which letter the code names, A, B or C, and whether the pedal or the throttle carries it
• Inspect both connectors for corrosion and push them home
• Watch both sensor signals on a scan tool while pressing the pedal slowly: they should rise smoothly
• Check the sensor reference voltage if several sensor codes appear together

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