P0666
PowertrainPcm Internalmoderate severityPCM/ECM/TCM Internal Temperature Sensor Circuit Range/Performance
What P0666 Means
The PCM detected the internal control module temperature sensor is out of the expected range. This sensor monitors the module's operating temperature.
Symptoms
- Check engine light on
- Possible performance issues
- No obvious drivability symptoms
Common Causes
- Faulty internal temperature sensor
- Overheated control module
- Poor module ventilation
- Faulty PCM
Diagnostic Steps
- Scan for codes
- Check module location for heat exposure
- Verify sensor data with scan tool
- Replace PCM if internal fault confirmed
🔌 Don't have a code reader?
Any of these will read and clear this code — pick by how deep you want to go.
Budget handheld~$40
ANCEL AD410 →
No-phone-needed handheld — reads, clears, live data, freeze frame.
✓ ANCEL official store
Serious DIY~$100
BlueDriver Pro →
Enhanced codes (ABS, airbag, TPMS) plus repair reports.
SHOP FAVORITEShop-grade tablet~$300
Autel MaxiCOM MK808S →
Bidirectional tests, service resets, all systems.
✓ Autel official store
Pro diagnostics$1,500+
Autel MaxiSys MS906 Pro →
Full-system pro platform — topology mapping, ECU coding, the works.
✓ Autel official store
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Community Confirmed Fixes
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