Originally Posted by jimSF

Does anyone have any suggestions on what items to check for a persistent Code 4 showing up? I have checked the vacuum hoses in my W140 '95 and found one that was disconnected several weeks ago, which I think caused the CE light to come on. I retrieved several codes via the "blinks" on the red light retrieval window. After checking and fixing the vacuum hoses I cleared all the codes as described by JimF and all codes went away. A few days later, CE light comes on again and gives 4 blinks. I've cleared the reader several times now and the CE will eventually come back on and give 4 blinks on the LED.

There are no symptoms that I can tell on the engine. The engine idles and runs well, as usual. It's just that the code 4 keeps showing up.

Any ideas? Thanks!