Throttle Position Sensor Circuit Out of Range (GM)
What does P1120 mean?
The P1120 code means the vehicle's onboard diagnostic system has detected: Throttle Position Sensor Circuit Out of Range (GM). This is a moderate severity code.
Common Symptoms
- Check Engine Light on
- Reduced engine power message
- Erratic or high idle
- Poor throttle response
- Vehicle may enter limp mode
Probable Causes (Ranked by Likelihood)
- Faulty throttle position sensor (TPS) Very High
- Damaged throttle body High
- Wiring issue between TPS and PCM Moderate
- Corroded TPS connector Moderate
- PCM failure Low
Step-by-Step Diagnostic Procedure
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Read TPS voltage with a scan tool at closed throttle and wide-open throttle
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Check for smooth voltage sweep from closed to open throttle (no dead spots)
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Inspect the TPS connector for corrosion or bent pins
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Test the 5V reference and ground wires at the TPS connector
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If TPS is part of the throttle body, consider replacing the entire throttle body assembly
Frequently Asked Questions
What does Reduced Engine Power mean with P1120?
When the PCM detects the TPS signal is out of range, it may activate Reduced Engine Power mode as a safety measure. This limits throttle opening to prevent unintended acceleration. The vehicle will feel sluggish.
Can I drive in Reduced Engine Power mode?
You can drive short distances at low speed, but the vehicle will have very limited power. It is best to pull over safely and have the vehicle towed or driven to a repair shop.
Do I need to reprogram the PCM after replacing the throttle body?
On some GM vehicles, the PCM needs to relearn the throttle body position after replacement. This may require a scan tool procedure or a specific key-on/key-off sequence. Check your vehicle service manual for details.