PeachParts Mercedes-Benz Forum - View Single Post - Check engine light – Code 4 (on plug itself

skybound · #7 04-16-2008, 08:46 PM

Just an FYI, I had the same problem with my 94 E320 after changing the head gasket. I know it is possible to inadvertantly switch the vaccum lines which I was careful not to do. The thing I did do though was to accidentally break the vacuum "T" (doesn't actually look like a "T", has 3 vacuum connections) that hooks to the top of the "switch over valve". I bought a new one at the dealer thinking I was done.
After driving the car the CEL came on, I checked the code and got the code #4. After reading this article I checked the vacuum lines to the SOV and for some reason no vacuum at the "T" fitting outlets. All the lines to the T were fine, but for some odd reason no vacuum at the outlets. It turns out I had a defective vacuum "T", there is a piece of hard vacuum line between the 2 outlets on the "T" that was obstructed somehow, I managed to run a small drill bit in the "T" and open the passage way, being careful not to puncture the rubber of the "T". Finally I had vacuum present at both outlets that connect to the SOV and no more CEL problems. I just thought I would pass this along for things to check when the code 4 is present.