Powertrain, generic · Computer and auxiliary outputs

P0638 Throttle Actuator Control Range/Performance Bank 1

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Throttle dirty, sooted or stiff
Icing from condensation in frost
Throttle motor or gears worn
Resistance in the motor control wires
Module or software

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

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–600
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

throttle bodythrottle actuator motorengine control module

Related codes

P0639P2101P2111P2112P2119P2135

References: law.cornell.edu, saabwisonline.com, saabwisonline.com, static.nhtsa.gov.