Code
P1122
CADILLAC
P — Powertrain
TP Sensor Circuit Intermittent Low Voltage
Views:
UK: 24
EN: 45
RU: 29
AI status
Completed
Completed
100%
Causes
- Open or short in TP sensor signal or reference wiring
- Poor or corroded connector/terminal at the throttle body or harness
- Intermittent ground or poor chassis/ECM ground
- Failed or internally intermittent throttle position (TPS) sensor
- Water intrusion or contamination in connector
- ECM input circuit fault (less common)
Symptoms
- Malfunction Indicator Lamp (MIL)/Check Engine Light illuminated
- Intermittent hesitation or stumble on acceleration
- Unstable or high/low idle, possible stalling
- Reduced throttle response or limp-home/reduced power mode
- Surging or inconsistent engine speed when accelerating
What to check
- Retrieve freeze frame and full scan tool data; record related codes and live TP sensor data
- Perform a visual inspection of the throttle body harness and connector for corrosion, damage, or moisture
- Backprobe the TP sensor connector and measure reference (VREF), signal, and ground with key ON and while moving throttle
- Wiggle test wiring and connector while monitoring live signal for intermittent changes
- Check continuity and resistance of signal and ground circuits to ECM (engine OFF)
- Compare TP sensor signal voltage against expected values at closed and wide open throttle
Signal parameters
- VREF (reference) to sensor: approximately 5.0 V (key ON)
- Signal voltage at closed throttle: typically ~0.2–1.0 V (varies by model)
- Signal voltage at wide-open throttle: typically ~4.0–4.8 V
- Signal should change smoothly and proportionally with throttle movement
- Intermittent low-voltage events: signal drops toward 0 V or below expected idle voltage
Diagnostic algorithm
- Connect a scan tool and record freeze-frame and live TP sensor values. Note when the low-voltage event occurs.
- Visually inspect the throttle body connector and wiring for damage, corrosion, bent pins, or water intrusion. Repair any obvious issues.
- With key ON (engine OFF), backprobe the connector: verify VREF ≈ 5 V, sensor ground continuity to chassis/ECM, and signal voltage at closed throttle. Verify battery voltage is stable.
- Slowly operate the throttle (or have an assistant) while watching live data. Look for smooth voltage change and any intermittent drops to low voltage.
- Perform a wiggle test: move the harness and connector while observing signal for intermittent faults. If fault is reproducible, isolate location and repair wiring/connector.
- Check continuity and for shorts: measure resistance from sensor signal pin to ECM input, and check for short to ground or to 12 V. Repair as needed.
- If wiring and connector are good, bench-test or replace the TPS with a known-good unit and re-check signal behavior.
- If problem persists after sensor and harness repairs, test the ECM input circuit or consult manufacturer guidance — replace ECM only after other causes eliminated.
- Clear codes, road test to confirm repair, and re-scan for return of P1122 or related codes.
Likely causes
- Wiring insulation damage with intermittent short to ground
- Corroded/loose connector at throttle body
- Failed TP sensor that intermittently drops output voltage
- Faulty sensor ground or VREF (5 V) supply to TPS
- Intermittent wiring harness contact caused by movement/vibration
Fault status
Status
Intermittent low voltage detected on the throttle position sensor signal circuit; possible intermittent open/short, poor connection, or sensor failure. DTC stored when signal drops below threshold.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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