P2D2CEngine Coolant Temperature Measurement System - Multiple Sensor Correlation
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- Engines with split or map-controlled cooling carry several coolant sensors, for example at head, block, inlet, outlet, radiator and heater core. After a cold soak all should read alike; P2D2C reports that the set as a whole disagrees and the module cannot single out one sensor. No manufacturer documents P2D2C publicly. GM's 2025 tables do the comparison under P0116 instead: once per valid cold start the coolant sensor is checked against two others from a configurable list that also includes oil, intake and outside air, Type B over two trips. CARB demands rationality checks of the ECT sensor and an approved plan for engines that read two sensors placed in different coolant loops. Warm-up enrichment and thermostat diagnosis may suffer.
- What you may notice
- Check engine light
- Temperature gauge or fan behaviour unusual
- Rough cold running or higher fuel use when warming up
- Likely causes
- LikelyOne coolant sensor in the set has drifted
- PossibleUneven soak, e.g. block heater or short stop, misread as a fault
- PossibleLow coolant or air leaving one sensor dry
- RareCorroded terminal shifting one reading
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €50 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.