Code Definition

P0638 — Throttle Actuator Control Range/Performance (Bank 1)

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0638

P0638 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0638 is stored, the module has detected a plausibility fault — the measured value is in the electrical range but is not consistent with expected operating behaviour; and a bank-specific fault, meaning it applies only to one cylinder bank of a multi-bank engine.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0638 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The Engine Control Module (ECM) operates the electronic throttle body through a small reversible DC motor and monitors the resulting throttle plate angle through two independent throttle position sensors built into the throttle body housing. DTC P0638 is set when the ECM commands the throttle plate to a target angle and the position feedback fails to follow that command within the expected time or to within the expected accuracy, indicating the actuator is not controlling the plate as intended. Common triggers include a throttle plate that is slow to move, that sticks at a particular angle, th...

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