P2BB8Engine Coolant Temperature Sensor 6 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 low signal from sensor 6 means a very small resistance that the ECM would have to read as extreme heat; in practice a signal wire touching ground or a shorted element. GM sets P2BB8 when the sixth coolant channel drops below 47.5 Ω in its 2019 L3B/common tables (19OBDG03D) or 55 Ω in the 2025 ECM tables (25OBDG03B), both roughly equal to 150 °C, if that persists for 5 of any 6 seconds; the fault is Type B, so the MIL comes on after the second trip. GM bulletin 21-NA-149 includes P2BB8 in the long list of codes caused by chafed engine harnesses on 2019–2021 light-duty pickups. Expect the cooling fans to run hard as a safeguard. If the same sensor's line is broken or touches battery voltage, P2BB9 is stored instead.
- What you may notice
- MIL on after two trips
- Sensor 6 shows an implausibly high temperature
- Radiator fans running at high speed
- Likely causes
- LikelySensor 6 signal wire shorted to ground, e.g. chafed harness
- PossibleInternally shorted sensor element
- RareMoisture or coolant in the connector bridging the pins
- 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: €30 – €350
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.