On some Mercedes-Benz models, the warning light may be illuminated, along with various fault codes relating to oxygen sensors stored in the onboard memory.  Here, febi provides a possible cause and solution to this problem.

Problem
The engine management warning lamp is illuminated, with various fault code entries, referring to the oxygen sensors logged in the engine control unit.

Cause
A malfunction of one - or both - of the oxygen sensors, due to the capillary action of the engine oil reaching the engine wiring harness. In turn, this affects the sensors via the camshaft-control solenoid valve.

Solution
Check all oxygen sensors for oil ingress and replace if necessary.

Check all camshaft-control solenoid valves for oil leaks and replace if necessary.

Locate any other contamination caused by loss of engine oil, and carry out any necessary repairs.

Install adaptor cable set 107574 between the camshaft-control solenoid valve and the engine wiring harness. The fine copper sleeves incorporated into this adaptor cable prevent the oil from spreading, reducing the risk of future electronic failures. It is recommended to install one adaptor cable for each camshaft-control solenoid valve fitted to the vehicle.

Check the engine oil level according to the manufacturer’s specifications and correct if necessary.