Carbon or dirt build-up on the throttle plate or bore causing sticking or slow movement; Worn or failing throttle body actuator motor or position sensors; Wiring damage, corrosion or poor connections in the throttle actuator or sensor circuits; Intake air leak after the throttle body upsetting airflow and throttle correction; Low or unstable supply voltage or poor earth affecting the throttle circuit; Faulty accelerator pedal sensor giving implausible demand signals; Engine control unit fault or outdated software, where a manufacturer bulletin confirms it.

P0639

Throttle Actuator Control Range/Performance Bank 2.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
6: AreaComputer and output circuits
39: FaultThe specific fault in that area

What it means

P0639 means the engine control unit has found that the throttle actuator on bank 2 is not performing as commanded, or is outside its expected control range. The unit compares the requested throttle angle with the position reported by the throttle position sensors and sets the code when the two disagree for too long. It is most relevant to engines with two throttle bodies, or where the manufacturer labels the throttle circuit as bank 2.

Symptoms

Engine warning light on, often with a throttle or powertrain warning message
Reduced power or limp-home mode with limited throttle response
Poor or erratic idle, or stalling at idle
Hesitation or delayed response when pressing the accelerator
Engine revs hanging or surging when coming off the throttle
Hard starting in some cases

Possible causes

Carbon or dirt build-up on the throttle plate or bore causing sticking or slow movementlikely
Worn or failing throttle body actuator motor or position sensorslikely
Wiring damage, corrosion or poor connections in the throttle actuator or sensor circuitspossible
Intake air leak after the throttle body upsetting airflow and throttle correctionpossible
Low or unstable supply voltage or poor earth affecting the throttle circuitpossible
Faulty accelerator pedal sensor giving implausible demand signalsrare
Engine control unit fault or outdated software, where a manufacturer bulletin confirms itrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting related throttle, pedal and intake codes
Check battery condition and charging voltage, and inspect the main earths, as low voltage can upset throttle control
Inspect the throttle body wiring and connectors for damage, corrosion, water ingress and bent pins
Look for intake leaks, split hoses or loose clamps between the air meter and the manifold
With the intake removed as needed, inspect the throttle plate and bore for carbon build-up and check the plate moves freely by hand with the ignition off
With a scan tool that shows live data, compare commanded and actual throttle angle and the sensor readings through the full range, watching for dropouts or mismatches
Check the supply, reference and signal voltages and the circuit resistance at the throttle connector against the manufacturer's data
Confirm which throttle or bank the manufacturer designates as bank 2 for this engine before condemning parts

How to fix

Clean the throttle body and plate using a method approved for the specific engine, then carry out the throttle adaptation or relearn if the vehicle requires it
Repair or replace damaged wiring, terminals or connectors in the throttle circuit
Replace the throttle body or actuator assembly if the motor or sensors are faulty, then perform the relearn procedure
Repair any intake leaks by replacing the damaged hoses, seals or gaskets
Restore proper battery and charging system condition and repair poor earth connections
Update the engine control unit software only if a manufacturer bulletin lists this as a known cause for the vehicle

Can I keep driving?

High severity

Avoid driving unless essential, as the car may drop into limp-home mode or lose power unexpectedly, which is unsafe in traffic. If it must be moved, keep the journey short and have it repaired promptly.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.