Code
P1121
INFINITI
P — Powertrain
Throttle Position Lower Than Expected
AI status
Completed
Completed
100%
Causes
- Faulty throttle position sensor (TPS) or throttle body assembly
- Corroded, damaged or loose wiring/connectors in TPS/throttle circuit
- Sticking or dirty throttle plate/throttle body
- Faulty accelerator pedal position (APP) sensor or sensor correlation error
- PCM/ECM software fault or internal failure
- Mechanical binding in throttle linkage (if applicable)
Symptoms
- Malfunction Indicator Lamp (MIL) or Check Engine Light illuminated
- Reduced engine power / limp-home mode
- Poor throttle response, hesitation or lack of acceleration
- Rough idle or stalling at low speeds
- Stored freeze frame data showing low TPS signal for commanded position
What to check
- Read and record freeze frame and live data with a scan tool (TPS, APP, throttle actuator position, commanded throttle)
- Visual inspection of throttle body, TPS connector and wiring for damage, corrosion or loose pins
- Check for related DTCs (APP sensors, throttle actuator, short to ground/voltage)
- Check for vacuum leaks and heavy carbon deposits on throttle plate
- Backprobe TPS signal and reference voltage with a digital multimeter or scope while operating throttle
- Wiggle test wiring while monitoring signal for intermittent faults
Signal parameters
- Reference supply typically ~5 V from PCM to TPS (verify in service data)
- Typical TPS signal voltage at closed throttle ~0.2–1.0 V (commonly ~0.5 V) and at wide open throttle ~4.0–5.0 V (varies by model)
- TPS voltage should rise smoothly and monotonically with throttle opening (no jumps or dropouts)
- Compare TPS signal versus accelerator pedal position (APP) and commanded throttle angle from scan tool for correlation
Diagnostic algorithm
- Retrieve DTCs and freeze frame data. Note engine conditions when code set.
- Clear DTCs, attempt to reproduce while watching live data (TPS, APP, commanded throttle, throttle actuator position).
- Perform a visual inspection of the throttle body, connectors and wiring harness for damage, corrosion, or pin push-out.
- With key on engine off, backprobe TPS: verify reference voltage (≈5 V) and ground. If missing, trace supply/ground to PCM.
- Slowly open throttle by hand (or with scan tool actuator) while monitoring TPS voltage; look for smooth, proportional increase. Repair/replace if signal is low or erratic.
- Compare APP sensor signal to TPS signal. If APP indicates driver demand but TPS remains low, suspect throttle body, internal throttle sensor, or wiring.
- Inspect and clean the throttle body if carbon buildup restricts plate movement. Relearn throttle/idle per manufacturer procedure after cleaning or replacement.
- If wiring and mechanical checks pass and replacement throttle/TPS does not correct, consider PCM/software update or replacement per service bulletin.
- After repairs, clear codes and verify proper operation under varied driving conditions; recheck for reappearance of P1121.
Likely causes
- TPS signal voltage stuck low due to internal sensor failure
- Broken or shorted signal wire to PCM (signal to ground)
- Poor connector contact or corrosion at TPS/throttle body harness
- Carbon buildup causing throttle plate not to follow command
- Mismatch between APP sensor and TPS signals (sensor out of calibration)
- Failed throttle actuator motor or position sensor inside electronic throttle body
Fault status
Status
P1121 — Throttle Position Lower Than Expected. Engine control module detected TPS or throttle position lower than expected for commanded position. MIL on; engine may enter reduced power mode.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email