Code
P1121
GMC
P — Powertrain
TP Sensor Circuit Intermittent High Voltage
Views:
UK: 29
EN: 53
RU: 41
AI status
Completed
Completed
100%
Causes
- Faulty throttle position (TP) sensor
- Loose, corroded or damaged connector at the sensor
- Wiring short to battery/5V reference or intermittent open
- Poor or intermittent ground connection
- Contaminated or mechanically damaged throttle body
- Intermittent ECM/PCM internal fault
Symptoms
- Check Engine Light (malfunction indicator lamp)
- Poor idle, idle surging or stalling
- Hesitation, reduced power or unresponsive throttle
- Limp-in mode on some vehicles
- Intermittent or unpredictable throttle behavior
What to check
- Read freeze frame and live data with scan tool; watch TPS voltage while slowly opening throttle
- Visual inspection of TPS connector and wiring for corrosion, pin damage, or loose terminals
- Backprobe TPS signal, reference (5V) and ground with key ON; note voltages
- Wiggle harness and connector while monitoring voltage/data to try to reproduce intermittent high reading
- Scan for related codes (pedal position, throttle actuator, CAN/communication errors)
- Check continuity/resistance between TPS pins and PCM connector with ignition OFF
Signal parameters
- Reference voltage: ~5.0 V (nominal)
- Sensor ground: near 0 V
- TPS signal voltage (closed throttle): typically ~0.2–1.0 V (manufacturer-specific)
- TPS signal voltage (wide-open throttle): typically ~4.0–4.8 V (manufacturer-specific)
- Intermittent high: sudden jumps above normal WOT voltage or unexpected spikes toward 5 V
Diagnostic algorithm
- Retrieve DTC details and freeze-frame data with a scan tool. Note operating conditions when fault occurred.
- Attempt to duplicate fault while monitoring TPS signal, reference and ground with a live-data tool. Wiggle the harness and connector to check for intermittent behavior.
- Visually inspect and clean the TPS connector and throttle body. Repair or replace corroded terminals and secure connector.
- Backprobe the TPS connector: verify constant ~5V reference with key ON, good ground, and that signal voltage changes smoothly with throttle travel. Look for spikes or drops.
- If signal shows intermittent high, disconnect TPS and verify signal at PCM connector to determine if fault is in harness/sensor or PCM. With sensor disconnected, signal should be open/low (depending on design).
- Check continuity and insulation of signal wire between TPS and PCM; repair any shorts (wire to 5V/battery) or opens. Repair harness using proper soldering/crimping and heat-shrink.
- Replace the TPS if wiring and connectors check good but signal is still intermittent/high.
- If new sensor and repaired harness still show intermittent high at the PCM input, consider PCM fault and consult manufacturer service info before replacement.
- Clear codes and road test to confirm repair; monitor for return of the DTC over multiple drive cycles.
Likely causes
- Corroded/loose sensor connector or pins
- Wiring harness shorted to 5V reference or battery voltage when moved
- Failed TPS producing intermittent high output
- Intermittent ground at engine/PCM
- Damaged insulation where harness rubs against metal
Fault status
Status
Intermittent high voltage detected on throttle position sensor circuit. Inspect sensor, connector and wiring for shorts to 5V or battery, poor ground, corrosion, or intermittent damage. Replace or repair faulty components as required.
Repair difficulty: Medium
Diagnostic time: 1.0 - 3.0 hours
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