Fault code P0638 – a step-by-step guide to diagnosing and fixing it

Error code P0638 is displayed and the check engine light is on - what does this mean?

The DTC P0638 is triggered by the OBD-II/EOBD system when a problem is detected with the throttle actuator control circuit "A". This fault code indicates a malfunction in the electronic throttle valve system, which is responsible for precisely controlling the air supply to the engine.

What can cause this error code?

• Defective throttle valve actuator motor
• Damaged wiring to the throttle valve system
• Corroded or loose plug connections
• Defective throttle body
• Faulty throttle position sensors
• Dirty or sticky throttle valve
• Defective engine control unit (ECU)
• Low battery voltage
• Mechanical blockage of the throttle valve

What symptoms occur in parallel with fault code P0638?

• Idle problems: Unsteady or fluctuating idling
• Acceleration problems: Delayed or jerky throttle response
• Reduced engine power: noticeable loss of power when driving
• Starting problems: Difficulty starting the engine or longer starting times
• Emergency running program: Engine runs in emergency mode with limited power
• Increased fuel consumption: Significantly higher fuel consumption than usual

How can the problem with error code P0638 be rectified?

• The repair requires a systematic diagnosis to identify the exact cause.
• Thoroughly clean the throttle valve and remove any deposits, then carry out a basic adjustment
• Check all electrical connections to the throttle valve system and replace or clean corroded plugs
• Replace the throttle actuator completely if there are mechanical defects
• Replace the entire throttle body if there is irreparable damage to the body or the sensors
• Completely replace the wiring to the throttle valve system if there are broken cables or insulation damage
• Check battery condition and replace battery or alternator if voltage is low
• Reprogram or replace the engine control unit if there are software updates or hardware defects