Code
P1121
GWM
P — Powertrain
- Throttle Position (TP) Sensor Circuit High Voltage
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on TPS signal wire
- Faulty throttle position sensor
- Poor or corroded connector or pin (signal or ground)
- Open or high resistance ground or reference circuit
- PCM/ECM input fault
- Aftermarket modifications or diagnostic equipment causing voltage backfeed
Symptoms
- Check Engine Light (MIL) on
- Reduced engine performance or limp mode
- Unstable or high idle
- Poor throttle response or hesitation
- Surging or unexpected acceleration in rare cases
What to check
- Scan for freeze-frame and live data (TPS voltage, throttle angle, pedal position)
- Compare TPS voltage to throttle pedal position sensor (correlation)
- Visually inspect TPS connector and wiring for damage, corrosion, or signs of short
- Backprobe TPS signal, reference (5V) and ground with a DVOM
- Wiggle harness while monitoring signal to reproduce fault
- Check battery voltage and charging system for over-voltage conditions
Signal parameters
- Reference supply: ~5.0 V (key ON)
- TPS signal typical range: ~0.5–4.5 V (closed to wide open throttle)
- High-voltage fault threshold: signal > ~4.8–5.0 V or equal to battery voltage
- Ground: near 0.0 V; high resistance grounds can cause incorrect readings
- Signal should change smoothly with throttle movement; abrupt jumps indicate wiring or sensor fault
Diagnostic algorithm
- Read and record trouble codes, freeze-frame data and live TPS voltage and throttle/pedal positions with a scan tool.
- Verify symptom and attempt to reproduce while watching live data (note exact voltage values and behavior).
- Visually inspect TPS connector and wiring for corrosion, pin damage, melted insulation, or aftermarket splices.
- With ignition ON (engine off), backprobe connector: measure reference voltage (~5 V), signal voltage (expected ~0.5–1.0 V at idle/closed), and ground continuity to battery negative.
- If signal is high, disconnect the TPS harness and measure signal wire at the harness connector. If signal remains high with sensor disconnected, suspect wiring short to battery/ignition or ECM issue.
- If signal drops when disconnected, test the sensor on bench (if possible) or replace with known-good sensor and re-test.
- Perform wiggle test on harness and connectors while monitoring signal to locate intermittent faults.
- Repair any damaged wiring, corrosion, or poor grounds. Reconnect and clear codes.
- If wiring and sensor check OK but issue returns, test or replace ECM input circuit per manufacturer procedures or consult technical service bulletins.
- After repairs, erase codes and perform a road test while monitoring TPS and pedal correlation to confirm correct operation.
Likely causes
- Damaged or contaminated TPS connector causing short to 12V
- Failed TPS (internal short or sensor drift)
- Wiring short to ignition-switched power or battery (+B)
- Poor ground at sensor or engine harness
- ECM input circuit fault (less common)
Fault status
Status
Throttle Position Sensor Circuit High Voltage detected. TPS signal voltage is above normal operating range or appears shorted to battery/ignition voltage.
Repair difficulty: Medium
Diagnostic time: 1–2 hours
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