P0638 Code: Throttle Actuator Control Range (B1) — Causes & Fix
P0638 means the throttle actuator control on bank 1 is out of range — the electronic throttle isn't reaching its commanded position.
- Applies to
- All OBD-II vehicles (any make or model)
- Est. repair cost
- $80 – $800
- Time to fix
- 30 minutes – 2 hours
What it means
Causes include a failing electronic throttle body, a connector fault, carbon binding the plate, or wiring problems. P0638 is a generic OBD-II code defined in the SAE J2012 standard, so it applies to virtually any 1996-or-newer OBD-II vehicle regardless of make. Fix the underlying fault, then clear the code with an OBD-II scan tool — it will return if the problem isn't resolved.
Symptoms
- Check engine light on
- Reduced power / limp mode
- Erratic idle or throttle response
How to fix it
- 1
Clean and inspect the throttle body
1. Check for carbon binding the throttle plate; clean it. 2. Inspect the connector and wiring.
- 2
Replace the throttle body
1. If it still won't reach commanded position, replace the throttle body, then clear the code.
Frequently asked questions
Why is my car in limp mode with P0638?
If the electronic throttle can't reach its target, the ECM limits power for safety. Cleaning or replacing the throttle body usually fixes it.
Last updated July 19, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.