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P0638 Generic (SAE) Basic entry

Throttle Actuator Control Range/Performance

Updated 2026-10-02 · Computer & output circuits

Severity
Medium
Typical repair cost
60 – 500 EUR
System
Powertrain

What it means

P0638 is stored when the Throttle Actuator Control signal is electrically valid but does not make sense compared with other sensors or the expected operating range. The circuit is usually fine; the component or what it measures is out of specification.

This entry is compiled automatically from the standard definition and typical diagnostic practice for this type of fault. A detailed, reviewed article is in preparation.

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Symptoms

  • Check engine light on
  • Engine may not start or runs in limp mode
  • Several unrelated codes stored at once
  • Erratic gauge or warning light behaviour

Common causes

  1. Throttle Actuator Control worn, contaminated or out of calibration
  2. Mechanical problem in the system the sensor measures
  3. Air, vacuum or exhaust leak influencing the reading
  4. Wrong or low-quality replacement part
  5. Wiring resistance causing a small voltage offset

How to diagnose

  1. Compare the live Throttle Actuator Control reading with a known-good value or a second sensor at idle and at 2500 rpm
  2. Check for air, vacuum or exhaust leaks that could skew the reading
  3. Inspect the component for contamination and clean it if the design allows
  4. Verify the part number is correct for the engine
  5. Replace the Throttle Actuator Control if the reading remains out of specification

Frequently asked questions

Can I keep driving with P0638?

Usually yes for a short time, but expect reduced performance or higher fuel use. Have it diagnosed within a few days.

Will clearing P0638 fix it?

No. Clearing only erases the stored code; it returns as soon as the monitor runs again unless the cause is repaired.

Related codes

P0639

Nearby codes in this group