P2BB4Engine Coolant Temperature Sensor 4 Circuit Intermittent/Erratic
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- This code covers jumps in the signal of the fourth coolant temperature sensor that coolant cannot physically make. GM explains the method in the 2019 edition of its engine tables for the L3B and related engines (19OBDG03D): from each reading and the sensor's time constant the software predicts an upper and a lower bound for the next sample, and a step beyond either counts as erratic; 5 s of failures inside a 6 s window set the code as Type B, MIL on the second trip, and it stays blocked while a hard circuit low/high fault is present. P2BB4 itself is missing from the 2025 tables. GM bulletin 21-NA-149 names it among the effects of a chafed engine harness on 2019–2021 GM light-duty trucks. A loose terminal is the classic cause; steady open or short faults are P2AFE and P2AFF.
- What you may notice
- MIL on after two drives
- Jumping temperature value in live data
- Cooling fans or thermal management reacting erratically
- Likely causes
- LikelyLoose or corroded terminal at the sensor 4 connector
- LikelyEngine harness chafed, wire making intermittent contact
- PossibleInternal intermittent break in the sensor element
- 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 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.