Code
P1121
HUMMER
P — Powertrain
Throttle Position (TP) Sensor Circuit Intermittent High Voltage
AI status
Completed
Completed
100%
Causes
- Faulty throttle position sensor (TPS)
- Damaged or chafed wiring harness
- Poor or corroded connector terminals
- Short to battery voltage (12V) on the TPS signal or reference
- Faulty ground at TPS or ECM
- Intermittent ECM input driver fault
Symptoms
- Check Engine / MIL illuminated intermittently
- Erratic or surging idle
- Poor throttle response or hesitation
- Intermittent limp-home or reduced power mode
- Stalling at idle or during low-speed maneuvers
- Throttle pedal feel may be inconsistent
What to check
- Read freeze-frame and live data with a scan tool; confirm code and note conditions when fault set
- Inspect TPS connector and wiring for damage, corrosion, bent pins or corrosion
- Backprobe TPS connector and measure reference (5 V), signal and ground with key ON
- Wiggle harness and connector while monitoring TPS voltage to reproduce intermittency
- Check for continuity and shorts: signal to 12V and signal to ground with ignition OFF
- Measure resistance to ground from TPS ground circuit and check ECM pin continuity
Signal parameters
- Reference voltage (VREF): ≈ 5.0 V (typically 4.75–5.25 V)
- TPS signal at closed throttle: ≈ 0.2–1.0 V (commonly ~0.3–0.6 V)
- TPS signal at wide open throttle: ≈ 4.2–4.8 V
- Signal should change smoothly with throttle position, no sudden jumps/spikes
- No valid TPS signal should exceed VREF or show sustained voltage near battery voltage (≈12 V)
Diagnostic algorithm
- Verify: Retrieve P1121 and any related codes. Note freeze-frame data (engine temp, rpm, throttle position, vehicle speed).
- Visual: Inspect throttle body, TPS connector and harness for damage, corrosion, heat or water entry. Repair obvious damage.
- Power/Ground: With key ON, backprobe the TPS connector. Confirm VREF ~5 V and solid ground. Repair any bad reference/ground before proceeding.
- Signal test: Slowly operate throttle while watching TPS signal on a scan tool or voltmeter. Look for smooth voltage change from ~0.3 V to ~4.5 V. If signal shows intermittent spikes or goes >VREF, proceed.
- Wiggle test: With probe connected, wiggle wiring and connector to reproduce the intermittent high voltage. If code or spikes reproduce, isolate and repair wiring/connector.
- Short checks: With ignition OFF, check continuity between TPS signal and battery + to detect intermittent short to 12 V. Also check continuity from signal to ECM input pin.
- Component swap: If wiring and connector are good and intermittent persists, replace the TPS. Re-test.
- ECM check: If new TPS and repaired wiring still show intermittent high voltage, suspect ECM input driver. Consult service information for ECM testing or replacement.
- Clear codes and road test under the same conditions that originally set the code to verify repair.
Likely causes
- Loose or corroded TPS connector pins causing intermittent high reading
- Wiring rubbed through and intermittently contacting a 12V source
- Internal TPS failure producing spikes above normal range
- Poor ground at throttle body causing erroneous voltage
- Aftermarket or replaced TPS with incorrect specification
- ECM intermittent input circuit failure (less common)
Fault status
Status
Intermittent high voltage detected on Throttle Position Sensor (TPS) signal circuit. ECM recorded voltage spikes or readings above normal threshold; fault stored when intermittency observed.
Repair difficulty: Medium
Diagnostic time: 1.0 - 2.5 hours
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