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DTC codes / P06xx · Computer and output circuits / P0639

P0639Throttle Actuator Control Range/Performance (Bank 2)

This code indicates that the powertrain control module (PCM) has detected a range or performance problem with the throttle actuator control (TAC) system on bank 2 of the engine. The PCM commands a specific throttle plate angle and monitors the actual position through a sensor; when the two do not match within a calibrated tolerance for a set time, it stores this code.

SystemPowertrain
Code typeGeneric (all makes)
SeverityHigh
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms.
  • Reduced engine power or limp mode, where the vehicle may be limited to a low speed.
  • A throttle pedal that feels unresponsive or requires more effort to accelerate.
  • Rough idle or stalling when coming to a stop.
  • Inconsistent engine speed or surging during acceleration.
  • A warning message on the dashboard such as 'Engine Power Reduced' or 'Service Throttle'.

Common causes, most likely first

  1. Carbon buildup or contamination on the throttle plate and bore, restricting movement.
  2. A faulty throttle position sensor (TPS) or accelerator pedal position (APP) sensor on bank 2.
  3. Wiring damage, corrosion, or loose connectors in the TAC motor or sensor circuits.
  4. A failing throttle actuator motor or its internal gears.
  5. A PCM software issue or internal fault in the throttle control driver.
  6. Mechanical binding in the throttle body linkage or return spring.
  7. Extreme temperatures or voltage drops affecting the TAC system performance.

How to diagnose and fix it

  1. Inspect the throttle body for carbon buildup and clean it with a throttle body cleaner and a soft brush.
  2. Check all wiring and connectors at the throttle body, pedal sensor, and PCM for damage or corrosion; repair as needed.
  3. Use a scan tool to monitor throttle position sensor voltages and compare commanded versus actual throttle angle; look for erratic or non-linear readings.
  4. Perform a throttle body relearn or calibration procedure with a scan tool after cleaning or replacement.
  5. Test the throttle actuator motor with a bidirectional scan tool to command the throttle plate open and closed while observing movement.
  6. If the throttle body is faulty, replace it with a quality unit and perform the relearn procedure.
  7. Verify the repair by clearing codes and test-driving the vehicle under various conditions to ensure the code does not return.

Common Misdiagnosis Traps for P0639

  • A dirty throttle body is the most frequent cause of this code, yet many technicians replace the entire throttle body without first attempting a thorough cleaning and relearn.
  • The code can be set by a weak battery or charging system issue that causes voltage spikes, so always check battery health and ground connections before condemning components.
  • Bank 2 designation on a V6 or V8 engine often refers to the throttle body that feeds the even-numbered cylinders, but on some engines it may refer to a specific throttle plate in a dual-throttle system; consult the service manual for the exact layout.
  • After replacing or cleaning the throttle body, a relearn procedure is mandatory; skipping it will cause the code to reset immediately even if the repair was successful.
  • Intermittent wiring faults can mimic a failed throttle body, so wiggle-test the harness while monitoring live data to catch poor connections.

Can I keep driving with P0639?

This fault can cause the vehicle to enter limp mode with severely reduced power, which is unsafe in traffic. Avoid driving until the issue is diagnosed; if you must move the vehicle, do so at low speed and be prepared for sudden power loss.

Tools that help

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

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