For the past three years, my car’s Check Engine light has been on because of
a Code 5 (EGR) fault. Since no EGR-related fault has ever been found, I
assumed the EGR tube was clogged.

Whenever I am under the hood, I routinely check and clear the codes. The
DM always flashes back 5 and, after being cleared, the Check Engine light
returns after about 4 restarts. (On one occasion it did not return until
after 7 restarts.)

After changing my oil this weekend, I started the engine to circulate the new
oil. Out of curiosity, I decided to check for codes, not expecting the
diagnostic module to work while the engine was running. Well, it did, and
flashed 5 back, as usual, and I cleared it, as usual, expecting to see the CEL
again in a short while.

Two days and at least 20 restarts later, the CEL has not returned. It
illuminates with the other dash lights on ignition, so I know the bulb is not
burned out. There appear to be several possibilities:

1. This is a fluke and at any moment the CEL will return, brighter and redder
than ever.

2. The clogged EGR tube spontaneously cleaned itself.

3. There never was an EGR fault; The car decided the 3-year practical
joke it was playing had run its course, and it was now time to stop.

4. I stumbled upon a little known, very groovy way to erase phantom
diagnostic codes.

5. I broke something, and the CEL will ever again illuminate in response to an
emissions fault.

1, 2, and 3 are unlikely. Four seems probable, and 5 possible.

Any good thoughts on this?

__________________
2008 E350 4matic / Black/Anthracite

------------------------------------
Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black