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DTC codes / Toyota codes / P1129

P1129 · ToyotaElectric Throttle Control System

P1129 on a Toyota means the engine control module (ECM) has detected a fault within the electric throttle control system, which is the drive-by-wire setup that replaces a physical cable with a motor-driven throttle plate. The ECM monitors the throttle position sensors, the throttle actuator motor, and the wiring between them, and it sets this code when the commanded throttle angle and the actual throttle angle disagree beyond a calibrated limit or when a circuit fault is detected.

SystemPowertrain
Code typeToyota specific
SeverityHigh
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • Illumination of the check engine light, often with the vehicle entering limp mode and limiting engine power
  • A throttle pedal that feels unresponsive, delayed, or excessively sensitive compared to normal operation
  • Rough or erratic idle, sometimes with the engine stalling when coming to a stop
  • A noticeable lack of acceleration or a sudden drop in power while driving
  • Often no symptoms besides the warning light, especially if the fault is intermittent

Common causes, most likely first

  1. Carbon buildup or mechanical binding on the throttle plate or throttle body bore, preventing the plate from reaching the commanded angle
  2. A failing throttle position sensor (TPS) inside the throttle body assembly that sends an inaccurate signal to the ECM
  3. Wiring damage, corrosion, or loose connectors in the throttle actuator motor circuit or the TPS signal circuit
  4. A worn or failing throttle actuator motor that cannot move the throttle plate smoothly or hold it at the commanded position
  5. A faulty accelerator pedal position sensor that misreports driver demand to the ECM
  6. A compromised ECM, though this is rare and should only be suspected after all other circuits and components are verified

How to diagnose and fix it

  1. Connect a scan tool and record all stored and pending codes, then check freeze-frame data for throttle position and accelerator pedal position at the time of the fault
  2. Visually inspect the throttle body bore and plate for carbon deposits or mechanical interference, and clean the bore with throttle-body cleaner if buildup is present
  3. Perform a resistance and voltage-drop test on the throttle actuator motor and the throttle position sensor circuits, checking for open circuits, shorts, and excessive resistance
  4. Back-probe the throttle position sensor signals at the ECM and compare them to the scan tool readings while slowly moving the throttle plate by hand to check for dead spots or erratic output
  5. Check the accelerator pedal position sensor signals for consistency and smooth progression through the full pedal travel
  6. If the throttle body is mechanically sound and the wiring is intact, replace the throttle body assembly and perform the required throttle body calibration or relearn procedure with the scan tool
  7. Clear the codes and road-test the vehicle through several drive cycles to confirm the fault does not return

What most technicians miss on P1129

  • A dirty throttle body is the most common cause of P1129 on Toyotas, and cleaning the bore and plate often resolves the code without replacing any parts, yet many people jump straight to a new throttle body.
  • The throttle position sensor and the throttle actuator motor are integrated into the throttle body on most Toyota engines, so a sensor fault usually means replacing the entire assembly rather than a separate sensor.
  • Intermittent wiring faults at the throttle body connector are easily missed because the connector can look fine visually; a wiggle test with the scan tool connected is essential to catch a loose terminal or chafed wire.
  • After replacing or cleaning the throttle body, the ECM must relearn the closed and open throttle plate positions, and skipping this calibration step will set P1129 again immediately on the first key cycle.
  • A weak battery or poor ground connection can cause voltage drops that the ECM interprets as a throttle actuator fault, so checking battery health and ground straps is a worthwhile first step before condemning the throttle body.

Can I keep driving with P1129?

If the vehicle has entered limp mode or the throttle response is erratic, avoid driving it because the ECM may not be able to control engine power predictably. Have the vehicle towed or driven only a short distance to a repair shop at low speed with hazard lights on.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Toyota vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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