Crankcase ventilation (PCV) valve codes

How its codes differ

• P052E is the engine computer saying the electrically controlled crankcase ventilation valve is not doing what it was commanded. On the Mercedes-Benz M274 engine a sticking, oil-coked valve is a known cause, but software and an overfilled crankcase come first.
• P050A (cold-start idle out of range) can come from a PCV fault, because a valve stuck open lets extra air into the intake and a blocked one changes how the engine idles. Vacuum leaks and throttle deposits are checked alongside it.
• P1101 on GM small turbo engines can point at crankcase pressure: GM bulletins tie it to crankshaft seal oil leaks and a whistle at start-up.
• Lean codes (P0171, P0174) are not linked to this page, but a PCV system that pulls in extra air is one of the air leaks a shop rules out for them.

Codes

• P052E

  Crankcase ventilation (PCV) regulator valve not working as expected

  Severity: Monitor

• P050A

  Idle speed off target just after a cold start

  Severity: Monitor

• P1101

  On GM and GM-era Saab engines, the airflow worked out from throttle position doesn't match the airflow measured by the MAF and MAP sensors

  Severity: Inspect soon

Signs it's failing

• Check engine light with P052E, P050A or P1101
• Rough or unsteady idle
• Oil leaks past seals or gaskets from crankcase pressure
• Whistle from the engine at start-up (some GM turbo engines)
• Oil in the intake hoses

How to test it

1. With the engine off and cold, check the oil level on the dipstick. An overfilled crankcase pushes oil into the ventilation hoses and valve and is a major cause of sticking valves on the Mercedes-Benz M274. (Low risk)

2. Look over the crankcase vent hoses for cracks, loose ends or oil soaking, and listen for a whistle from the engine at start-up. (Use caution)

   Warning: If you listen with the engine running, keep hands, hair, clothing and tools clear of the fan and belts, and do not run the engine in a closed garage. Engine parts get hot enough to burn.

3. Read and note all stored codes with a scan tool, and ask a dealer whether a software update or bulletin applies to your VIN before parts are replaced. (Low risk)

4. Measuring crankcase vacuum, checking the valve's control circuit and replacing an electrically controlled valve are jobs for a shop. On the M274 the valve takes several hours to replace. (Best left to a shop)

   Warning: These tests are done with the engine running and involve hot engine parts and electrical back-probing. Leave them to a shop.

After the repair

• Confirm the oil level is at, not above, the full mark.
• Use a replacement valve and hoses that match the original part; similar-looking valves can be calibrated differently.
• Clear codes only after the repair, then drive normally over several days with both city and highway driving so the readiness monitors can complete; clearing codes or disconnecting the battery resets them to not ready, which fails an emissions test.