P2B51B Camshaft Profile Actuator B Control Performance/Stuck Off Bank 1
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- MIL on immediately (Type A)
- Exhaust lift profile no longer changes, turbo response may feel different
- Cylinder deactivation disabled
- Likely causes
- LikelyExhaust actuator B pin releases without command, often heat-related sticking
- PossibleFaulty Hall feedback in the actuator or its signal line
- RareSludge or debris at the actuator bore hindering the pin
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.