Powertrain, generic (extended)

P2B5B Engine Coolant Flow Control Valve Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P2B5B covers a short to battery voltage on the motor leads of the coolant flow control valve. GM's diesel table 25OBDG04B evaluates it through the driver stage as well: a current above 9 A with a lead tied to supply counts as a failure, and the usual 80-of-100 rule with 12.5 ms sampling stores a Type B code. GM bulletin 21-NA-149 names P2B5B in its LM2 harness-chafing condition together with blown fuses and rough running, which points at wiring rubbing on powered circuits rather than at the valve. Because the driver shuts down to protect itself, the valve no longer reacts and warm-up control is lost. Ground short and open are P2B5A and P2B59.

Likely causes

Motor lead chafed against a powered circuit (GM LM2, 21-NA-149)
Corroded or wet connector bridging to supply
Driver stage in the engine control module faulty

Symptoms

  • MIL on after two drives, possibly further codes from the same harness
  • Blown fuses or rough running if the harness is chafed
  • Weak heater output during warm-up

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

P2B59P2B5AP2B5C

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