P0667
PCM / ECM / TCM Internal Temperature Sensor Range/Performance
Powertrain Network/Communication PCM Internal Sensor 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

The engine computer has an internal temperature sensor that's reading outside normal limits or isn't responding correctly. Think of it like a thermometer in the computer itself that's broken or giving wildly inaccurate readings.

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Symptoms You May Notice
3 known symptoms for this code
Check Engine Light illuminated
Potential limp mode or reduced performance
Possible cooling fan operation issues
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Embedded Systems Insight
What the ECU/ECM is actually computing

The PCM monitors its own internal die temperature using a built-in sensor to prevent overheating and manage performance. If the sensor reads beyond expected voltage ranges or shows erratic fluctuations, the ECU logs this fault. The ECM uses this temperature data to adjust fuel timing, emission controls, and cooling fan activation.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Internal Temp Sensor Voltage 0.5–4.5V (typically −40°C to +120°C equivalent) <0.2V or >4.8V, or rapid fluctuations
Internal Die Temperature −40°C to +105°C operating Out-of-range or implausible rate of change
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Battery terminals and connectors
Clean corrosion from battery posts and ECU connectors; loose connections can cause false temperature sensor readings.
2
ECU connectors and wiring harness
Inspect for water intrusion, damaged pins, or corrosion on the PCM connectors and reseat firmly.
3
Engine Control Module (ECM/PCM)
If connector and power checks pass, the internal sensor in the ECU may be faulty and require replacement or reprogramming by a dealer.