Why does my Mercedes GLC check engine light keep coming on?

Short answer: A GLC check engine light that comes and goes needs the codes read. One GLC 300 owner's dealer found P052E, a blocked crankcase ventilation valve, and fixed it under extended warranty. A new clunk after a tire rotation means check the lug nuts right away.

Symptom: The check engine light turns on and off, or a clunk started after tires were rotated.

What to check first

1. Get the codes read and keep the list.
2. Ask if extended warranty covers the crankcase ventilation valve.
3. Check your VIN at nhtsa.gov/recalls.
4. After any tire service, recheck the lug nut torque.

Likely causes

1. Crankcase ventilation valve actuator. The crankcase ventilation valve vents engine gases back into the intake. One owner's dealer found it blocked and set code P052E.
2. Other stored codes. A check engine light can have several causes. The codes point where to look.
3. Loose lug nuts after service. A clunk right after a tire rotation can mean the wheels weren't tightened.

What it usually costs

The owner's repair was free under extended warranty. Out-of-warranty prices weren't posted.

Is it safe to keep driving?

A steady check engine light usually lets you drive to the shop. A flashing light means stop. Loose lug nuts are dangerous; don't drive until they're tight.

DIY or shop?

Reading codes and checking lug nuts are DIY. The valve repair is shop work.

Recalls, bulletins and complaints in plain words

• Related recalls: NHTSA lists GLC recalls in these years, including 20V364000 (some 2020 GLC300s, screws on the turbocharger oil lines may not be tight, which can leak oil), 21V961000 (some 2019-2020 GLC300s, particles may be trapped between the fuel rail and injectors) and 23V445000 (some 2021-2022 GLCs, the fuel pump may shut down and cause a loss of drive power). None is about the crankcase ventilation valve. Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Plain words: The recalls above aren't about this owner's problem, but check your VIN.
• NHTSA complaints: 220 keyword-matched complaints for Mercedes-Benz GLC 2016–2022 (of 639 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-28; keywords: check engine, engine light, warning, stall, loss of power). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In Mercedes 2018 GLC 300 - Check Engine Light on Car Talk, a 2018 GLC 300's check engine light came and went for a long time. The dealer found code P052E71, a blocked crankcase ventilation valve actuator, and fixed it under the extended warranty with a plug and software update. Members said to get the exact codes and consider an independent Mercedes shop.
• In Mercedes glc on Car Talk, a GLC owner heard a clunk after a tire rotation. Members said to check the lug nuts right away.

Quick tip

Always ask for the code itself. It's your starting point.

Vehicle focus: Mercedes-Benz GLC, 2016-2022.

Safety / mechanic note

Loose wheels are a crash risk. Verify with a mechanic.