Powertrain, generic (extended)

P2BB8 Engine Coolant Temperature Sensor 6 Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Sensor 6 signal wire shorted to ground, e.g. chafed harness
Internally shorted sensor element
Moisture or coolant in the connector bridging the pins

Symptoms

  • MIL on after two trips
  • Sensor 6 shows an implausibly high temperature
  • Radiator fans running at high speed

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–350
Time0.5–2.5 h

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

Parts involved

engine coolant temperature sensor 6wiring harnessecm

Related codes

P2BB9P2BB6P2BB7P2B2DP2AFEP01E5

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.