P2AFEEngine Coolant Temperature Sensor 4 Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- Coolant sensors are NTC thermistors, so a signal from sensor 4 that is too low stands for an impossibly hot reading, usually a signal wire grounded or a shorted element. GM documents P2AFE for the 2.7 L turbo four (L3B) in its 2019 tables: the configurable temperature input system sets it when the resistance of the sensor 4 channel drops below about 41 Ω, corresponding to 150 °C, for 5 s within a 6 s window; Type B, so the MIL follows on the second trip. In bulletin 21-NA-149 GM names P2AFE as one consequence of engine harness chafing on 2019 to 2021 Silverado and Sierra 1500 trucks, the 2.7 L included. Because a hot reading is first taken at face value, the fans may run at full speed. P2AFF is the opposite fault, P2AFD the plausibility check.
- What you may notice
- Check engine light after two trips
- Cooling fans running at full speed
- Implausibly high coolant temperature in live data
- Likely causes
- LikelySignal wire shorted to ground, for example by harness chafing
- PossibleInternally shorted sensor
- RareFaulty input in the engine control module
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €30 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.