P0638 code meaning
Throttle Actuator Control Range/Performance Bank 1
Powertrain system Generic code P06xx codes Check engine light
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. 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.
P0638 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0638
- 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 of P0638
- Most likelyThrottle dirty, sooted or stiff
- PossibleIcing from condensation in frost
- PossibleThrottle motor or gears worn
- PossibleResistance in the motor control wires
- Less likelyModule or software
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Throttle bodyThrottle actuator motorEngine control module
What each part of P0638 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 6 | Area: computer (engine control module) and output circuits. |
| 38 | The exact fault in that area. |
What to do next
- Note P0638 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0638
What does P0638 mean?
P0638 means "Throttle Actuator Control Range/Performance Bank 1". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0638?
Drive gently and only to a workshop. With P0638 the car can go into limp mode (reduced power) to protect itself.
Will P0638 fail an emissions test?
Yes, it can. P0638 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0638 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0638 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.