Yellow Engine Diagnostics Warning Lamp

[The Mad Monk]

I have a W211 220CDI E Class. Yesterday I (foolishly?) used a garden hose to wash the leaves from under the bonnet and around the bottom of the windscreen - with the bonnet up.

When I drove the car the yellow engine diagnostics lamp remained on and the engine was misfiring. The misfiring cleared, but the yellow light remains on.

Started the car a few times this morning, it seems to run ok, but the yellow light remains on.

Any ideas, please?

[Scrump]

It may go out after a few more miles or starts (it did on my wife’s car after a similar incident).
Otherwise buy a cheap OBD II tool and reset it yourself (assuming you don’t have one or know someone with one you can borrow).

[The Mad Monk]

Scrump said:

It may go out after a few more miles or starts (it did on my wife’s car after a similar incident).
Otherwise buy a cheap OBD II tool and reset it yourself (assuming you don’t have one or know someone with one you can borrow).

I read somewhere that disconnecting the battery may clear the problem. Worth a try?

[Scrump]

I have heard that as well. No idea if there is any truth in it though.

[The Mad Monk]

I thought I might as well try the 'disconnect the battery' thing to see if that worked. Got the toolbox out, took the cover off the battery, thought I had better check that the light is still staying on (the poor Mercedes only goes ou a couple of times a week). started the engine and
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The light went out and stayed out!!!

I can only think that my hosing under the bonnet had got water somewhere where it shouldn't be and took a took a while to finally dry out..