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· Registered
Donkey cart w/CEL
370 Posts
Discussion Starter · #1 ·
Need someone out there with a set of stones and an Actron CP9175 OBDII scanner- or any generic scanner to try this little experiment.

Read below-

Could it be the MIL on OBDII mercedes be triggered by checking Emissions Monitor status with a handheld scanner?

Ok, here's a weird one:

Over the last week I've been chasing down a driveability problem my 96 C36 (M104) random stalling (turns out the MAF was the culprit FYI)

Got the car running flawlessly, decided to chase down some other things discovered including a burned out CEL (turns out the bulb was out- was reading codes off my Actron CP9175 scanner)

Of course, after replacement of the bulb, and still driving the car around to test to see if the random stalling has gone away. Car was perfectly fine drive - wise.-

During this time I'm monitoring the readiness status of the various emissions systems over the last 3k miles I've changed so many sensors I wanted to make sure everything was working as it should.

The MIL came on during driving around-scanning for actual codes produced a PASS NO CODES FOUND.

Been chasing this issue for the last 3 days, the CEL eventually shut off when I turned the car on without starting and let it sit in run. Of course, During this time I was checking status and scanning for codes and it would flip on.

I finally got it to shut off yesterday and didn't have the scanner plugged in. went for a 45 minute drive today and while sitting in a Starbucks drive thru decided to plug the thing back in -

In the back of my mind I was thinking about Murphy's law and how the MIL was going to pop up while I scan and I sure as hell was right.

- checking for codes got a PASS- no codes found

- checking Monitor status, I looked down and checked values, looked up at my dash and sure enough, MIL was staring straight at me.

Unplugged my scanner, shut car off, turned key to run and let it sit there and the MIL shut off (approx 15 seconds)

As an experiment, I plugged my scanner in again, and went to check monitor status and sure enough, MIL again.

Shut car off, turn to run, repeat and it's off again.

5x I did this.

So, could the MIL coming on after plugging in the scanner and checking monitor just be a test to show the light is working? Once again the only way it shuts off is if you put the car to run and let it sit there then it shuts off on it's own.

Of course, the light stays off if the scanner is unplugged and i'm minding my own business.

Anyone out there experience this? If this is the case, I've been chasing my own tail for 4 days now..


· Registered
Donkey cart w/CEL
370 Posts
Discussion Starter · #2 ·
Someone in the W202 forum said the 96 models are plagued with false MIL's- he says this came from CARB themselves.

Mine had a dead bulb, and now I think I know why.

If you pull up to the smog station with the MIL on they may automatically fail you and force you to spend $$$ to fix it.

With the blown bulb in place they are forced to plug it in to scan it.

Blown bulb is now back in my dash and case closed. I don't need problems at smog.
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