Why is oil getting into the wiring on my Mercedes C300?

Short answer: On many C300s, the camshaft adjuster magnets leak oil into their electrical plugs. The oil can creep along the wiring. Replace the leaking part early and add oil-stop adapter cables so it doesn't damage the harness.

Symptom: Oily residue on top of the front of the engine, oil in the magnet plugs, a burning-oil smell, or a check-engine light.

What to check first

1. Unplug each camshaft magnet connector (engine off) and look for oil inside the plug.
2. Check the cam position sensor plugs nearby for oil.
3. Get any check-engine codes read.
4. If oil is in a connector, have the harness checked for oil further along before it reaches the engine computer.

Likely causes

1. Leaking camshaft adjuster magnet. The camshaft adjuster magnets (solenoids that control valve timing) sit on the front of the engine. Their seals can let oil seep out through the electrical plug.
2. Oil wicking into the engine harness. Once oil gets into the plug, it can travel inside the wires toward other connectors and, in bad cases, the engine computer. Owners add short 'sacrificial' adapter cables so oil can't travel past them.
3. Leaking camshaft position sensor. The cam position sensors nearby can leak oil into their connectors the same way.

What it usually costs

These threads did not give reliable prices. The magnet is cheaper than a harness, which is cheaper than an engine computer. Catching it early saves the most.

Is it safe to keep driving?

A small seep isn't an emergency, but oil in wiring can cause timing faults or running problems. Fix it before it spreads.

DIY or shop?

Swapping a camshaft magnet is a common DIY on many C-Class engines. Harness or computer replacement is shop work.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA lists 31 recall(s) for the Mercedes-Benz C300/C-Class in these years, and none match this problem. Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Plain words: The complaint count below shows how often owners reported problems that mention these words to NHTSA. A count is not proof of a defect.
• NHTSA complaints: 15 keyword-matched complaints for Mercedes-Benz C300/C-Class 2015–2021 (of 1299 unique complaints queried, NHTSA complaints API by model year, queried 2026-11-08; keywords: oil leak, camshaft, cam magnet, wiring harness, oil in) (NHTSA returned no data for 2 model-year queries). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In Camshaft oil leak into wiring harness on Reddit r/w204, a C-Class owner posted about oil leaking from the camshaft area into the wiring harness.
• In 2014 C300 Oil leaking into wiring harness on MBWorld, a 2014 C300 owner reported oil leaking into the wiring harness.
• In Oil in Engine Wiring Harness- How to Fix It, Permanently, For Cheap. on BenzWorld, owners shared a low-cost way to stop oil from reaching the harness after the leaking part is replaced.

Quick tip

If you have a C300, pop the cam magnet plugs off once a year and look. It's a five-minute check.

Vehicle focus: Mercedes-Benz C300 (W204 and W205, about 2008–2021). Cam magnet leaks are reported on several Mercedes gas engines.

Safety / mechanic note

Oil near hot exhaust parts is a fire risk. Verify with a mechanic.