Powertrain, generic (extended)

P2B5F Engine Coolant Flow Control Valve Position Sensor Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P2B5F is set when the valve position signal sits above the top of its window. The 2025 Duramax calibration (3.0 L, 25OBDG04B) treats a SENT raw value over 98 % of 5 V as implausibly high and stores a two-trip Type B code after 80 of 100 readings, sampled every 6.25 ms while the SENT link itself is healthy. A signal shorted to the 5 V reference or to supply, a moisture path in the connector or an internal sensor fault are the usual explanations; GM's 21-NA-149 lists P2B5F with the LM2 harness-chafing codes as well. Coolant flow control switches to a fallback, which can show as slow warm-up or weak cabin heat. Low counterpart: P2B5E.

Likely causes

Signal wire shorted to the 5 V reference or to battery voltage
Moisture or corrosion bridging contacts in the valve connector
Position sensor in the valve faulty

Symptoms

  • MIL on after two drives
  • Slow warm-up or weak cabin heat

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–1,500
Time0.5–8 h

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

Parts involved

engine coolant flow control valvewiring harnessecm

Related codes

P2B5DP2B5EP2B60

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