P0866
PowertrainModule Communicationmoderate severityTCM Communication Circuit High
What P0866 Means
The transmission control module communication circuit voltage is higher than the expected threshold. This is often caused by a short to voltage or a failed module.
Symptoms
- Transmission warning light
- Erratic shifting
- Reduced power mode
Common Causes
- Short to voltage in circuit
- Faulty TCM
- Corroded connector
- Faulty PCM
Diagnostic Steps
- Retrieve stored codes
- Measure circuit voltage at TCM
- Check for short to power source
- Inspect connectors and wiring
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