Clearing Diagnostic Codes with Engine Running Erases them Permanently ?? - PeachParts Mercedes-Benz Forum

EricSilver · #1 03-16-2008, 07:24 PM

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?

stevebfl · #2 03-16-2008, 08:27 PM

I like #3.

deanyel · #3 03-16-2008, 08:46 PM

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

stevebfl · #4 03-16-2008, 08:56 PM

Poetic justice!

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

black beaut-E · #5 03-17-2008, 07:46 AM

Quote:

Originally Posted by stevebfl

Poetic justice!

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

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

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.

Arthur Dalton · #6 03-17-2008, 10:06 AM

uhhhhhh..

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

EricSilver · #7 03-17-2008, 01:13 PM

Quote:

Originally Posted by Arthur Dalton

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.

EricSilver · #8 03-17-2008, 01:13 PM

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.

Texholdem · #9 03-17-2008, 01:18 PM

Quote:

Originally Posted by EricSilver

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.
...

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

EricSilver · #10 03-17-2008, 01:19 PM

Quote:

Originally Posted by black beaut-E

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

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

EricSilver · #11 03-17-2008, 01:21 PM

Quote:

Originally Posted by Texholdem

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

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

Arthur Dalton · #12 03-17-2008, 01:23 PM

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.

Texholdem · #13 03-17-2008, 01:23 PM

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

EricSilver · #14 03-17-2008, 01:31 PM

Quote:

Originally Posted by Arthur Dalton

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

Oops, OK.

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