Code
P1120
LEXUS
P — Powertrain
Accelerator Pedal Position Sensor Circuit Malfunction
Views:
UK: 25
EN: 71
RU: 34
AI status
Completed
Completed
100%
Causes
- Damaged, corroded, or disconnected APP sensor connector or wiring
- Short to battery or ground in signal or reference circuit
- Open circuit or high resistance in signal/ground
- Faulty accelerator pedal position sensor/pedal assembly
- Faulty ECM or poor ECM ground (less common)
- Water intrusion or contamination at the pedal connector
Symptoms
- Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL) illuminated
- Reduced engine power or limp-home mode
- Poor or delayed throttle response
- Erratic idle, hesitation, or surging during acceleration
- Possible inability to start (rare) or fixed engine speed behavior
What to check
- Read stored freeze frame data and full DTC list with a scan tool
- Inspect APP sensor connector and wiring for damage, corrosion, or water
- Check reference voltage (typically 5V) at the sensor harness
- Measure signal voltage(s) while slowly moving pedal from rest to full travel
- Verify proper sensor grounding at chassis/ECM
- Perform wiggle test on harness and connector while monitoring live data
Signal parameters
- Reference supply: approximately 5.0 V (should be stable with ignition ON)
- Signal output: typically varies with pedal travel in ~0.3–4.5 V range (sensor A increasing, sensor B often follows different ramp or inverse depending on design)
- Idle/rest voltage: around 0.2–1.0 V (depends on vehicle, verify with data)
- Full-throttle voltage: near 4.0–4.8 V (depends on sensor)
- Two-sensor correlation: sensors should change smoothly and maintain expected relationship; sudden jumps, flatlines, or matching voltages (short) indicate faults
Diagnostic algorithm
- Connect an OBD-II scanner. Confirm P1120 and record freeze frame/live APP sensor data (both channels if present).
- Visually inspect APP sensor connector and harness for damage, pin corrosion, bent pins, or water. Repair any issues.
- With ignition ON (engine off), verify presence of stable 5V reference at the sensor connector and a good ground reference. Replace/repair wiring if reference or ground missing.
- Backprobe sensor signals. Slowly press pedal and observe voltage traces for smooth, monotonic change. Compare Sensor A vs Sensor B (if present) for expected correlation; look for dead zones, jumps, or identical signals (indicative of short).
- Wiggle harness and connector while monitoring live signal for intermittent faults. Check for continuity and shorts to battery/ground on suspect wires.
- If wiring and connectors test good, swap in a known-good pedal assembly (or bench-test replacement sensor) and re-check signals and codes.
- If replacement pedal cures the fault, clear codes and perform road test to verify. If fault persists with a known-good sensor, investigate ECM power/ground and connectors; consider ECM bench test or replacement.
- After repairs, erase DTCs and verify no return of P1120 and that throttle response returns to normal.
Likely causes
- Loose/corroded connector at APP sensor
- Wiring chafed where harness passes through bulkhead or near pedals
- Intermittent open/short in signal wire causing inconsistent voltage
- Failed APP sensor internal potentiometer or Hall-effect elements
- Poor sensor ground
Fault status
Status
Accelerator Pedal Position Sensor Circuit Malfunction detected by ECM. May cause limp mode, reduced power, and abnormal throttle response. Inspect pedal sensor, wiring, and ECM connections.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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