Throttle/Pedal Position Sensor A Circuit Malfunction
The P0120 code means the vehicle's onboard diagnostic system has detected: Throttle/Pedal Position Sensor A Circuit Malfunction. This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- medium
- Estimated cost
- $30-$120 for TPS; $150-$400 for electronic throttle body
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Common Symptoms
- Check Engine Light on
- Hesitation or stumble on acceleration
- Erratic idle speed
- Engine may enter limp mode
- Throttle unresponsive
Probable Causes (Ranked by Likelihood)
- Faulty throttle position sensor (TPS) Very High
- Wiring damage or corrosion at TPS connector High
- Throttle body carbon buildup affecting TPS sweep Moderate
- PCM throttle input circuit fault Low
Step-by-Step Diagnostic Procedure
-
Monitor TPS voltage with a scan tool during slow throttle opening from idle to WOT. It should sweep smoothly from about 0.5V to 4.5V.
-
Any dropout, spike, or dead zone in the sweep indicates a failing TPS.
-
Check connector for corrosion and loose pins.
-
Clean throttle body if carbon is restricting plate movement.
-
Measure TPS voltage at rest: should be 0.45-0.55V on most applications.
Common Fixes by Vehicle
What techs usually find when diagnosing P0120 on specific vehicles — tap your vehicle for the fix and the exact part:
2009-2020 Ford F-150/Explorer 3.5L/5.0L Easy DIY
Throttle position sensor circuit malfunction. On modern Ford trucks, the TPS is integrated into the electronic throttle body. Check the 6-pin connector for backed-out pins or corrosion. If voltage is erratic with key on, the throttle body assembly needs replacement (Motorcraft 9W7Z-9E926-A). Perform an idle relearn after installation.
Labor: 30-45 min2007-2017 Toyota Camry/Corolla 2.5L Easy DIY
TPS circuit A malfunction. The TPS is integrated into the throttle body on the 2AR-FE. Check for 5V reference voltage at the connector with key on. If reference voltage is missing, trace the wiring back to the ECU. If voltage is present but the signal is erratic, replace the throttle body assembly (Denso 22030-28070). Perform throttle relearn after replacement.
Labor: 30-45 min2002-2015 Nissan Altima/Sentra 2.5L QR25DE Easy DIY
TPS circuit has a dead spot or erratic signal. On the QR25DE, clean the throttle body first with throttle body cleaner. Check the TPS connector for corroded pins. If the signal drops out during slow throttle sweep, the throttle body needs replacement. Perform the idle air volume relearn procedure after installation.
Labor: 30 minFrequently Asked Questions
What is a TPS and what does it control?
The throttle position sensor measures the angle of the throttle plate. The ECU uses this to calculate how much fuel to inject, adjust ignition timing, and control transmission shift points.
Can I adjust a TPS to fix P0120?
On older cable-throttle engines with adjustable sensors, sometimes. On modern drive-by-wire systems, the TPS is sealed inside the throttle body and cannot be adjusted.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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