What P0638 means
The electronic throttle motor positions the throttle plate; P0638 means the actuator does not follow its command on bank 1 (or the only throttle): target and actual angle from the two position sensors differ, or the motor needs too much duty cycle to hold the position.
How the engine computer detects it
Subaru (also sold as Saab 9-2X) sets it at more than 3.5° deviation for 250 ms or over 95 % duty cycle for 2 s, lights the lamp at once and lets the spring set the plate to about 6° – raised idle, almost no power. GM's Saab 9-4X V6 uses more than 80 % duty cycle for over 1 s, lamp in the first trip. Mazda's CX-9 set it after frosty nights when condensation froze the throttle and fixed it with software that moves the plate after switch-off. Ford reports the same function as P2111/P2112.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine or electronic throttle light
- Limp mode: much reduced power, raised idle
- Delayed or jerky throttle response
- Often after a cold start in frost
Common causes
- Throttle dirty, sooted or stiff Most likely
- Icing from condensation in frost Possible
- Throttle motor or gears worn Possible
- Resistance in the motor control wires Possible
- Module or software Less likely
How to diagnose P0638
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: throttle body, throttle actuator motor, engine control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Vehicles that report P0638 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Kia Sorento | 2008–2013 | 3 | — |
Counts of owner complaints to the NHTSA that mention P0638 (13 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 6
- Computer and output circuits
- 38
- Specific fault
Questions drivers ask
Can I drive with code P0638?
Drive gently and only as far as you need to. The engine computer may limit power to protect the engine, so avoid highways and heavy traffic until it's fixed. If the check engine light starts flashing, pull over.
Will my car pass an emissions inspection with P0638?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Can I fix P0638 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.
Often reported together
Codes that owners mention in the same NHTSA complaints as P0638. They can point to a shared cause, so it's worth checking them together.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.