Powertrain, generic (extended)

P2B5A Engine Coolant Flow Control Valve Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P2B5A stands for a short to ground in the control wiring of the coolant flow control valve motor. GM's 2025 table for the 3.0-litre Duramax describes the detection: the driver sees more than 9 A flowing, which it interprets as one motor wire touching ground, and 80 out of 100 samples at 12.5 ms set a two-trip Type B fault once relay voltage exceeds 11 V. Unlike P2B58, where the motor itself draws too much current, the cause here is normally insulation damage in the harness, a pinched wire near the valve or water in the connector. The valve stays in its last or default position, so coolant distribution becomes fixed. Short to power is P2B5B, open circuit P2B59.

Likely causes

Motor wire chafed or pinched against ground
Coolant or water in the valve connector
Internal short to housing in the valve motor

Symptoms

  • MIL on after two drives
  • Engine temperature control fixed, slower warm-up or higher running temperature

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–1,500
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

P2B59P2B5BP2B58

References: gsi.ext.gm.com, law.cornell.edu.