Possible causes

– Drive-by-wire control system malfunction
– Throttle actuator malfunction
– Throttle valve malfunction
– PCM malfunction

Tech notes

Dirty or clogged throttle body can triggered the P0638 code. Before replacing any parts try cleaning the throttle body and reset the engine light.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P0638 VOLVO Description

The Powertrain Control Module (PCM) compares the actual Throttle Possition (TP) with the target TP when the engine is running. If the difference is more than the specification, the PCM determines that there is a throttle actuator control circuit range/performance problem.