Clearing Diagnostic Codes with Engine Running Erases them Permanently ??
 

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?

I like #3.

I would have voted for #1 - why #3?

Poetic justice!

And besides there is no way the light will be brighter if it appears again.

uhhhh
 

I'm no english major, but I think the brighter and redder was just ment to be a ironic funny.:D

I have had that same light for a while now and it even prevented me from passing my emmision test. the mechanic said I had to drive it for a few days to eliminate the code not just from the dash but also from the memory in the car's computer before I could emission's computer would allow it to go forward and complete the emission's test.

uhhhhhh..

Why didn't your mechanic simply reset your Diagnostics Module Memory??????????????????

He/They did, numerous times (or so they say). But the problem never went away. That was the mystery.

Day 3: No CEL

I will give it a full week, and then check the DM again.

If I get 5 flashes, then Alternative #5 is true, and I broke something.

If I get no flashes, then #5 or #4 could be true, but I am not sure.

If I get a single flash, then #4 is definitely true.

How did you pass the state inspection the past 3 years? Were you able to clear CEL before the inspection each time?

Yes, it was. Thanks for sparing me the need to point that out. :)

Yes. Also, in Virginia, emmissions, are done every 2 years so the CEL was not an issue for the anual mechanicals.

Mt post was in responce to post #5.
..but on your EGR, the suspect would be the EGR sticking b/c it has not been upgraded to the modified EGR with the smaller diameter shaft.. There is Benz Campaign on that chassis for the change over.

Just do a simple hand vac test at the egr port while car is at idle.

You're lucky, in Texas we have to do it annually :sigh:

Oops, OK.

I would prefer that the issue, if any, is the EGR itself since it is directly accessible. Will check that out.

Please, Arthur Dalton, ....
 

which engines does the EGR campaign apply to? Is there a reference number for it?

TIA.