Code
P1120
CADILLAC
P — Powertrain
Throttle Position (TP) Sensor 1 Circuit
Views:
UK: 24
EN: 62
RU: 33
AI status
Completed
Completed
100%
Causes
- Damaged or corroded TPS connector or wiring (opens/shorts/poor pin contact)
- Failed throttle position sensor (potentiometer or hall element)
- Faulty 5V reference or sensor ground from ECM
- Contaminated/throttle plate binding or mechanical throttle body wear
- Intermittent connection from vibration or repair work
- ECM internal fault or software calibration error
Symptoms
- Malfunction Indicator Lamp (MIL)/Check Engine Light ON
- Erratic or poor idle, surging or stalling at idle
- Delayed, reduced or inconsistent throttle response
- Engine enters limp/reduced-power mode
- Difficulty accelerating or hesitation on throttle application
What to check
- Read stored DTCs and freeze frame data with scan tool
- Confirm vehicle specific code definition and any manufacturer notes
- Visually inspect TPS connector, pins and wiring harness for damage or corrosion
- Check for related codes (throttle actuator, pedal position, CAN bus)
- Backprobe TPS pins and observe live data while slowly moving throttle
- Measure 5V reference and sensor ground at connector
Signal parameters
- Reference voltage: ~5.0 V (usually 4.8–5.2 V) present at TPS reference pin
- Sensor ground: ~0 V (low resistance to chassis/ECM ground)
- Output voltage closed throttle: ~0.1–1.0 V (varies by manufacturer)
- Output voltage wide-open throttle: ~4.0–4.8 V
- Signal should change smoothly and monotonically with throttle opening — no jumps or dropouts
- Typical potentiometer resistance range: 0–5 kΩ (varies by sensor design)
Diagnostic algorithm
- Safety first: set parking brake, chock wheels, work in well-ventilated area with engine off when inspecting components
- Connect compatible scan tool, record freeze frame and live TPS data, note whether code is current or historic
- Visually inspect TPS connector and wiring for damage, corrosion, or looseness; repair or replace damaged sections
- With ignition ON (engine off), backprobing: verify 5V reference present at TPS reference wire and stable
- Measure continuity/resistance from TPS ground pin to chassis/ECM ground; repair poor grounds
- With engine running or key ON depending on procedure, monitor TPS output voltage while slowly moving throttle from closed to wide open — look for smooth change without jumps
- Perform wiggle test on harness and connector while watching live data to identify intermittent faults
- If wiring and connectors are good, swap with known-good TPS or install new OEM-equivalent throttle position sensor and clear codes
- After repair or replacement, perform throttle body/TP sensor relearn or throttle calibration per manufacturer procedure if required
- Retest under road conditions and verify no recurrence of code and normal driveability
Likely causes
- Broken/frayed TPS signal wire or chafing to ground
- Loose or corroded connector at throttle body
- TPS internal failure due to wear or contamination
- Lost 5V reference from ECM or poor ground
- Throttle body carbon causing abnormal sensor readings
Fault status
Status
Stored fault: Throttle Position (TP) Sensor 1 Circuit — signal out of range, intermittent, or implausible. Inspect TPS, wiring, reference and ground; repair and retest.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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