What Does P0638 Mean?
The PCM has detected that the electronic throttle actuator (throttle body motor) on Bank 1 is not responding within the expected range or performance parameters. The actual throttle plate position does not match the PCM's commanded position, indicating a mechanical or electrical issue with the drive-by-wire throttle system.
Safety Warning
Vehicle will likely enter reduced power/limp mode, limiting speed to 15-30 mph. Sudden throttle response changes are possible. Drive only to the nearest shop.
Common Causes
35%
Carbon buildup on throttle body bore restricting plate movement
30%
Faulty electronic throttle body motor or internal gear failure
20%
Throttle position sensor (TPS) within the throttle body providing inaccurate feedback
15%
Wiring harness issue between PCM and throttle body (high resistance)
Diagnostic Steps
1
Step 1: Monitor commanded throttle position vs. actual throttle position PIDs in live data — a consistent deviation of more than 5% confirms the performance issue.
2
Step 2: Visually inspect the throttle body bore and plate for carbon buildup — clean with throttle body cleaner and a soft brush if deposits are present.
3
Step 3: After cleaning, perform the throttle body relearn procedure per the manufacturer's service manual (typically involves key cycling and idle relearn).
4
Step 4: If the code returns after cleaning and relearn, measure the throttle motor resistance (typically 1-10 ohms) and TPS signal voltage (should sweep smoothly from 0.5V to 4.5V).
5
Step 5: If the motor or TPS is out of specification, replace the throttle body assembly — these components are not typically serviceable separately.
Estimated Repair Cost
$100 - $800
Parts + labor, varies by vehicle and location
The PCM has detected that the electronic throttle actuator (throttle body motor) on Bank 1 is not responding within the expected range or performance parameters. The actual throttle plate position does not match the PCM's commanded position, indicating a mechanical or electrical issue with the drive...
The most common cause of P0638 (Throttle Actuator Control Range/Performance (Bank 1)) is: Carbon buildup on throttle body bore restricting plate movement
Typical repair costs for P0638 range from $100 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle will likely enter reduced power/limp mode, limiting speed to 15-30 mph. Sudden throttle response changes are possible. Drive only to the nearest shop.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0638 to identify the root cause.
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Quick Info
Category
Powertrain
System
Electronic Throttle Control
Difficulty
Type
Generic (SAE)
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