Code
P1129
SCION
P — Powertrain
Electronic throttle control system malfunction
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UK: 4
EN: 7
RU: 5
AI status
Completed
Completed
100%
Causes
- Faulty throttle body / throttle actuator motor
- Faulty accelerator pedal position (APP) sensor or throttle position sensor (TPS)
- Open, shorted, corroded or damaged wiring/connectors in ETC circuits
- Low battery voltage or poor ground
- Blown fuse or failed relay supplying the ETC
- PCM/ECM fault or software issue
Symptoms
- MIL/Check Engine Light illuminated
- Reduced engine power or limp-home mode
- Poor or delayed throttle response, hesitation or surging
- Engine may idle erratically or stall
- Throttle position indicated by scan tool does not match pedal input
What to check
- Read and record all stored codes and freeze-frame data with a scan tool
- Check battery voltage (key on/engine off and cranking) and engine grounds
- Inspect fuses and relays related to ETC/throttle and replace if blown
- Visually inspect throttle body, APP sensor and wiring harness/connectors for damage or corrosion
- Monitor live data: APP sensor channels, TPS/throttle angle, PCM commands, and compare for logical correlation
- Attempt throttle actuator command with a factory scan tool (follow vehicle procedures) to observe response
Signal parameters
- 5 V reference present at APP/TPS connectors (key ON) — should be stable
- APP sensor output(s): nominally ~0.5–4.5 V across pedal travel (exact values vary by model)
- TPS/throttle angle feedback: angle or voltage should change smoothly and correspond to APP inputs
- Dual-channel APP correlation: both channels should vary proportionally and not contradict each other
- No diagnostic trouble code for low battery voltage; CAN bus/PCM communication should be present
Diagnostic algorithm
- Connect a professional scan tool, read all DTCs and freeze-frame. Note related codes (APP, TPS, CAN, low voltage).
- Verify battery condition and charging system; ensure battery voltage >12.4 V with key on. Check engine grounds.
- Visually inspect connectors and wiring for the throttle body and accelerator pedal. Wiggle harnesses while monitoring live data for intermittent faults.
- Check fuses/relays for the ETC circuit and replace if faulty.
- Monitor live data: at rest and while slowly pressing pedal, verify APP channel voltages change smoothly and TPS/throttle angle follows commands. Look for out-of-sync or implausible values.
- Measure 5 V reference and ground at sensors. Confirm continuity back to PCM. Repair wiring faults found.
- Command the throttle actuator with a scan tool (actuator test) and observe movement and feedback. If actuator does not respond or feedback is incorrect, suspect throttle body assembly.
- If throttle body is contaminated, clean per service procedure and retest. After repair, clear codes and perform required throttle / idle relearn or PCM adaptation per service manual.
- If wiring and sensors are good but problem persists, consider PCM/software update or replacement as directed by factory service information.
- After repairs, road test and verify the fault does not recur; re-scan for codes.
Likely causes
- Contaminated or sticking throttle plate interfering with position feedback
- Intermittent connector or corroded pins at throttle body or accelerator pedal
- Failed dual-channel accelerator pedal sensor with inconsistent channel outputs
- Broken or shorted signal/5V reference wiring to APP or TPS
- Failed throttle actuator/motor or its internal potentiometer
Fault status
Status
Electronic Throttle Control System Malfunction — PCM detected inconsistent or implausible signals from the throttle control circuit/components. Vehicle may be in reduced-power (limp) mode. Inspect sensors, wiring, throttle body, fuses and PCM communications.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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