P0638Powertrain
Powertrain · SAE
Throttle Control Unit — Implausible Signal
Meaning
The ECU has detected that the feedback or command signal from the electronic throttle control (ETC) unit is implausible relative to the requested position. The system cannot verify that the actual throttle position matches the commanded position.
Common causes
- Faulty electronic throttle body (ETC) or failed DC motor
- Integrated throttle position sensor inside the ETC reporting an incorrect signal
- Damaged wiring between the ECU and the throttle body
- Corroded or intermittent throttle body connector
- Internal ECU fault in the ETC drive circuit
Symptoms
- Check-engine light (MIL) on
- Limp-home mode with limited throttle opening (typically 10–15 %)
- Severely limited or absent acceleration
- Idle irregularity
- Possible engine stall
Severity
High: the electronic throttle body is critical for engine management; limp-home mode severely limits drivability.
What to do
- Read ETC live data with a scan tool: compare requested and actual throttle positions
- Verify throttle body supply voltage and ground
- Check wiring between the ECU and throttle body for shorts and open circuits
- Mechanically clean the throttle body of carbon deposits
- Replace the throttle body if the motor or internal sensors are faulty