Powertrain, generic (extended)

P2B51 B Camshaft Profile Actuator B Control Performance/Stuck Off Bank 1

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

On the exhaust camshaft (B) of bank 1 the second sliding-cam solenoid is monitored by P2B51. GM applies it to the L3B 2.7-litre turbo four, whose exhaust side carries two such actuators. Its table entry mirrors the intake check: the ECM tracks the Hall feedback of the pin and treats a drop below the extending level of 55 without any shift request as an unintended firing. Four mismatches within five cylinder-event readings, engine running and supply above 11 V, store the code as Type A. In practice a pin that fires by itself can push the exhaust sleeve into the wrong profile, so exhaust lift and cylinder deactivation are blocked. NTN-SNR names it actuator never active. Intake equivalent: P2B4F; circuit faults: P2B39–P2B3B.

Likely causes

Exhaust actuator B pin releases without command, often heat-related sticking
Faulty Hall feedback in the actuator or its signal line
Sludge or debris at the actuator bore hindering the pin

Symptoms

  • MIL on immediately (Type A)
  • Exhaust lift profile no longer changes, turbo response may feel different
  • Cylinder deactivation disabled

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–700
Time0.5–3 h

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

Parts involved

b camshaft profile actuator b b1wiring harnessecm

Related codes

P2B55P2B4FP2B52P2B39P005A

References: gsi.ext.gm.com, gsi.ext.gm.com, ntn-snr.com, law.cornell.edu.