P0599
PowertrainEngine Coolingmoderate severityThermostat Heater Control Circuit High
What P0599 Means
The thermostat heater control circuit voltage is too high. This usually indicates an open circuit or short to voltage in the heater control line.
Symptoms
- Check engine light on
- Engine warms up slowly
- Temperature gauge unstable
Common Causes
- Short to voltage in heater circuit
- Open in heater control wiring
- Faulty heated thermostat
- PCM driver failure
Diagnostic Steps
- Retrieve stored codes
- Check heater circuit for short to power
- Verify continuity to PCM
- Test thermostat heater command with scanner
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