Powertrain, generic (extended)

P2BB4 Engine Coolant Temperature Sensor 4 Circuit Intermittent/Erratic

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Loose or corroded terminal at the sensor 4 connector
Engine harness chafed, wire making intermittent contact
Internal intermittent break in the sensor element

Symptoms

  • MIL on after two drives
  • Jumping temperature value in live data
  • Cooling fans or thermal management reacting erratically

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–400
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

engine coolant temperature sensor 4wiring harnessecm

Related codes

P2AFCP2AFDP2AFEP2AFFP2BB5P01E7

References: gsi.ext.gm.com, static.nhtsa.gov, law.cornell.edu.