Code
P1121
CADILLAC
P — Powertrain
TP Sensor Circuit Intermittent High Voltage
AI status
Completed
Completed
100%
Causes
- Faulty throttle position (TPS) sensor
- Intermittent short to battery voltage on the signal wire
- Poor or corroded connector or pin contact at TPS
- Damaged, chafed or broken wiring harness to TPS
- Faulty 5V reference or PCM internal fault
- Aftermarket electrical accessory or poor splice introducing voltage
Symptoms
- Check Engine Light / MIL illuminated (intermittent)
- Intermittent throttle hesitation, surging, or stumble
- Unstable or high idle at times
- Reduced engine performance / possible limp-home mode
- Difficulty reproducing the problem (intermittent nature)
What to check
- Read freeze frame and stored data with a scan tool; note engine conditions when code set
- Check for additional related DTCs (other TPS, reference voltage, or communication codes)
- Visually inspect TPS connector and wiring for damage, corrosion, melted insulation, or aftermarket splices
- Backprobe TPS connector and measure signal voltage at key ON, engine OFF and during throttle travel
- Check 5V reference and ground at TPS while moving harness and connector (wiggle test)
- Perform continuity and short-to-power/short-to-ground tests on TPS signal and reference circuits
Signal parameters
- Reference voltage: typically stable ~5.0 V (check OEM spec)
- Signal voltage at closed throttle: typically ~0.4–1.0 V (vehicle-specific)
- Signal voltage at wide open throttle: typically ~4.0–4.9 V (vehicle-specific)
- Signal must change smoothly with throttle movement and not show rapid high-voltage spikes
- Intermittent high voltage: brief excursions above specified signal max or sudden jumps toward battery voltage
Diagnostic algorithm
- Record freeze-frame data and any related codes. Clear codes and attempt to reproduce while monitoring live TP sensor data.
- Visually inspect TPS connector, pins and wiring harness from TPS to PCM. Repair any visible damage or corrosion.
- Backprobe TPS connector. With key ON engine OFF, verify 5V reference is present and constant. Check sensor ground for low resistance to chassis/PCM ground.
- Measure TPS signal voltage at closed throttle and slowly open throttle. Expect a smooth change from low to high within the specified range. Note any spikes or sudden jumps.
- With a scan tool or meter, perform a wiggle test on the wiring and connector while watching the signal for intermittent high readings. Also wiggle harness near harness clamps and connectors.
- Check continuity of signal and reference wires to the PCM and test for shorts to battery voltage and ground. Repair any wiring faults found.
- If wiring and connector check OK but intermittent high voltage continues, replace the TPS sensor and retest.
- If replacement TPS does not clear the issue, suspect PCM/internal reference problem or an external device injecting voltage; further diagnosis at the PCM or module-level may be required.
- After repairs, clear codes and road-test under conditions similar to freeze-frame. Re-scan to ensure code does not return.
Likely causes
- Wiring harness damage or connector corrosion causing intermittent high voltage
- TPS sensor internal failure (intermittent)
- Loose or compromised connector pin allowing intermittent contact to battery voltage
- Aftermarket device or poor splice feeding voltage into signal wire
Fault status
Status
PCM detected intermittent high voltage on the Throttle Position Sensor signal circuit. This may cause intermittent throttle control or drivability issues and requires inspection of the sensor, connector, wiring, and reference/ground circuits.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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