Code
P1120
TOYOTA
P — Powertrain
Accelerator Pedal Position Sensor Circuit
Views:
UK: 22
EN: 67
RU: 36
AI status
Completed
Completed
100%
Causes
- Faulty accelerator pedal position (APP) sensor
- Damaged, corroded or loose connector at the pedal sensor
- Open, shorted, or chafed wiring between sensor and ECM (to 5V reference, signal, or ground)
- Water intrusion/corrosion in connector or sensor
- Poor or missing ground or Vref (battery/ignition supply) issues
- Intermittent harness damage (broken strands, pinched wiring)
Symptoms
- Check Engine MIL/SES lamp on
- Reduced engine power / limp mode
- Poor or delayed throttle response
- Vehicle surging, stumbling, or hesitation on acceleration
- Possible hard start or stall in extreme cases
- Codes may be intermittent depending on wiring movement
What to check
- Read stored DTCs and freeze-frame data; record RELATED DTCs (other APP/TPS codes)
- Use a scan tool to view live APP sensor voltages/percentages for sensor 1 and sensor 2 while pressing the pedal
- Check for battery voltage and good chassis and sensor ground at pedal connector
- Inspect pedal assembly connector and wiring for corrosion, bent pins, water damage, or physical damage
- Backprobe Vref (usually ~5V), ground, and signal pins with ignition ON and compare to scan tool data
- Wiggle harness with engine running or with scan tool data active to look for intermittent faults
Signal parameters
- Reference voltage (Vref): ~5.0 V (typical) at pedal connector with ignition ON
- Sensor output (APP sensor 1): ~0.5–4.5 V across pedal travel (idle ≈ low end, full throttle ≈ high end)
- Sensor output (APP sensor 2 / redundant): should vary similarly and correlate closely with sensor 1 (difference usually
- Ground continuity:
- Open circuit: infinite/very high resistance between sensor signal and ECM pin
- Short to battery: signal ~= battery voltage (≈12V) — indicates short to power; short to ground: signal ≈ 0V
Diagnostic algorithm
- Confirm code P1120 and note any additional TPS/APP codes and freeze-frame data with a scan tool.
- With ignition ON (engine off), inspect pedal connector and wiring for corrosion, bent pins, water, or damage. Repair or clean as needed.
- Backprobe connector: verify Vref ≈5V, good ground, and measure signal voltage at rest and while moving pedal. Compare to expected ranges and to secondary sensor if present.
- If Vref or ground is missing, trace and repair power/ground circuits (fuses, relays, connectors, harness).
- Wiggle harness and connectors while monitoring live data to find intermittent opens/shorts. Repair damaged section or secure wiring.
- Check continuity between sensor pins and ECM connector pins; repair any open or high-resistance circuits. Check for shorts to battery or ground.
- If wiring and connectors test good but sensor output is out-of-range or not changing properly, replace the APP sensor/pedal assembly.
- After repair or replacement, clear codes and perform a test drive while monitoring APP signals to confirm proper operation and no return of the fault.
- If fault persists after sensor and wiring repairs, consider ECM input circuit testing or replacement (refer to manufacturer service info).
Likely causes
- Corroded/loose connector at the pedal assembly
- Open/short in the signal wire caused by harness chafing near firewall or pedal
- Failed APP sensor (internal pot or hall sensor degraded)
- Water ingress in pedal connector or sensor housing
Fault status
Status
P1120 — Accelerator Pedal Position Sensor Circuit fault. ECM detected abnormal or inconsistent signal from the APP sensor circuit (open/short/intermittent/out-of-range). May trigger reduced power mode.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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