Throttle Actuator Control Range/Performance (Bank 2)
Diagnostic trouble code P0639 indicates that the engine control module has detected a range or performance issue with the Throttle Actuator Control (TAC) system on Bank 2. The computer sets this code when the actual throttle valve position on the second bank of cylinders fails to match the commanded position within a specific timeframe.
This code is considered high severity because a malfunctioning throttle actuator can cause unpredictable acceleration, stalling, or force the vehicle into a severely restricted limp mode. It should be diagnosed and repaired immediately to ensure safe driving.
Common symptoms
- Illuminated Check Engine Light
- Vehicle enters reduced power or 'limp' mode
- Poor or no response to accelerator pedal input
- Rough idling or engine stalling
- Uneven engine performance between cylinder banks
Likely causes
- Carbon buildup or binding in the Bank 2 throttle body
- Faulty Bank 2 throttle actuator control (TAC) motor
- Damaged wiring or loose connections in the Bank 2 TAC circuit
- Defective Throttle Position Sensor (TPS) on Bank 2
- Faulty Accelerator Pedal Position (APP) sensor
- Powertrain Control Module (PCM) software issue or failure
What to check before replacing parts
Visually inspect the wiring harness and connectors for the Bank 2 throttle body.
Look for: Look for frayed wires, corroded pins, or loose connections that could interrupt the signal between the PCM and the throttle actuator.
Inspect the Bank 2 throttle body for carbon buildup and binding.
Look for: Check if the throttle plate is stuck or heavily coated in carbon, which would prevent smooth operation and cause a performance mismatch.
Monitor Throttle Position Sensor (TPS) and Accelerator Pedal Position (APP) data using a scan tool.
Look for: Verify that the TPS readings for Bank 2 smoothly follow the APP sensor inputs without dropping out, spiking, or lagging significantly.
Test the Bank 2 throttle actuator motor circuit for proper resistance and voltage.
Look for: Compare the measured resistance of the TAC motor to factory specifications; an open or shorted motor indicates internal failure.
Check for manufacturer Technical Service Bulletins (TSBs) and PCM software updates.
Look for: Determine if there is a known software glitch affecting the Bank 2 throttle control logic that requires a PCM reflash to resolve.
This page explains the generic P0639 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
Gear guide: Best OBD2 ScannersRead this code yourself next time — from $20 Bluetooth dongles to bidirectional scan tools.Rather have a pro handle it? Find a vetted local mechanic.