P0638 fault code: what it means

P0638: Electronic throttle is not reaching the position commanded. Car usually goes into reduced-power mode.

Engine and gearbox (powertrain) · Costly if missed

Usual causes, most likely first

carbon build-up in the throttle body
worn throttle motor or gears
faulty throttle position sensor in the throttle body

P0638 by make

Volvo

Throttle actuator control range/performance. Volvo electronic throttle (ETM) faults bring 'reduced engine performance'.

Usual causes: faulty electronic throttle module; dirty throttle body; throttle wiring

What the repair usually costs

Throttle body clean and idle relearnNZ$90–NZ$190 · A$100–A$200
Electronic throttle body replaceNZ$470–NZ$1,290 · A$440–A$1,190
Intake valve carbon clean (walnut blast, direct injection)NZ$530–NZ$1,190 · A$560–A$1,240

Not sure what P0638 means on your car? Ask Credov.

Before you clear it

Write the code down or photograph the scanner first. A code that comes straight back after clearing points to a fault that is still there. A car whose codes were cleared just before you arrived may be hiding one: the scanner's readiness monitors show "not ready" for a while after codes are cleared.

Researched by Credov from manufacturer and workshop sources. A fault code points to where a fault may be; a workshop confirms it with a diagnosis. Browse all fault codes.