"Check Engine" Light On ML-320
 

My check engine light just came on. I'm wondering if it has anything to do with the fact that my brother filled up the truck using 87 octane fuel the other day? Could that be the cause? Thanks in advance

If he filled the tank and didn't screw the cap on correctly (three turns until you here the rachety clicking sound), that will set the CE light off.

Recheck the gas cap first before you panic...

The loose fuel cap is a possibility. Most times you also get a blinking low fuel light immediately before the check engine light comes on in a situation like this. Another scenario we get here quite often in Wisconsin this time of year is the engine may have been left running during the refuelling. That'll do it every time. 87 octane? I'm not sure if that'll do it or not. Any driveability concerns? Usually a check engine light caused by poor fuel will be set by misfire codes, in other words it's bad gas and it'll run bad and that's where the code comes from. In general it should handle the 87 octane once in a while, not as a steady diet though. Take into account the amount of "good" fuel in the tank before the 87 was put in, as this will raise the octane number of what's in the tank.
Gilly

Thanks for the replies, checked the cap, it was tight, so I just filled it with 93 octane, and I will drive it for a while. So far drives great, I'll check back and give results.

Well, after several miles of driving, light stayed on. So in my infinite wisdom, I decided to disconnect the battery to see if I could reset the light. Well, it did, and hasn't come on in a couple of days. Now I have to find out where I put the code for my stereo.

Mine came on after a tank of bad gas on Thursday. It pissed me off because I had to drive 500 miles to Chicago. It went off after about 600 miles and another full tank of gas.

The codes should be in your stereo manual. At least mine were the last time I looked.

Kuan

Check Engine Light On 2000 Ml-320
 

Filled tank with gas and rrove about 50 miles. Went to a meeting and began driving back home. The engine misfired or hesitated, then ran OK.
About half way home the "CHECK ENGINE" LIGHT CAME ON STEADY. but the truck ran OK.
After about 4 days the light remained on so I had the dealer read the error code. It indicated that the Mass Air Flow sensor was out of range. They recalibrated the sensor and the light went out. They said that "sometimes" this will fix the problem.
It fixed it for one day and the light came back on. The mechanic also asked me what grade gas I was using. I told him mid range and he said it was OK to use 87 octane instead. So I switch to 87 or regular.
In the meantime I cleaned the MAS with an utrasonic cleaner (the type you clean jewery with) using purified water and then dried the sensor with air.
(suggested by an Engineer that manufactures MAS's for another company, Not Bosch)

Now the light is off part of the time and on part of the time. I will be switching back to mid grade gas ASAP.

Now I don't know if it's the MAS sensor or the regular gas.

Anyone have any input? Is gas Octane a real potential issue?
Thanks

when the CEL is on, you have to have the codes read, even if only by someone at AutoZone (they'll do it for free with a universal OBSII device). if you're throwing codes 1073 and/or 1077, it's probably a bad MAS [your cleaning technique is intriguing, but most posts I've read don't give me much confidence in any cleaning method]. do a search of CEL or AMM, MAS or MAF; somewhere there's some great advice by blackmercedes that pertains to replacing the air filter and cleaning out it's housing often to avoid fouling the MAS. if you don't want to spend the $300 for a new MAS, try ebay: I just bought one for $40 and another for $30. but correct the fault first, or you'll just fry another MAS.

I appreciate your help on the issue.
Currently the CEL is off again so if I were to replace the MAS while the light is out or off, will I fry or damage the new MAS?

I do have a local Auto Zone so if it comes back on I could have the codes read.

Also just filled up with med range gasoline.

Thanks again

I'm a little baffled by the on-and-off nature of your CEL (of course, I am mechanically inept); but I would at least try to clean out the air filter housing, maybe even clean the MAS again (I might try that jewelry cleaner technique with my old MAS, which I didn't have the heart to throw away). another great post re: this issue was by stevebfl, who posted a link to a superb article--technical but informative. search.

Interesting, the one thing I forgot to mentioned is this whole situation happened shortly after the 50,000 service performed by the dealer. Maybe some dirt did get jogged around in the air intake.

Well I'll let you know how it goes over a week or so.

Right now I'm going to let the high octane gas get into the system and keep my hands off !

Regards

Just a quick contribution to this CEL thread. It seems that my 99 320 has had this malfunction light on for about 75% of the time since it was a year old. Four different shops have read then cleared the codes but the light always came back on within a week. At different times I've been told that the MAS or the purge valve may have been at fault. Codes reported to me include: PO300, 301, 130, 135, 170, 173, 302, 303, 442.

The purge valve was replaced about two years ago but the CEL was not out for long. Last summer when the MAS signal was again reported out of range, it ws changed. Following replacement of the MAS, the light stayed out -- for about a hundred miles.

In all this time, the vehicle has only stumbled once (while trying to pass a truck about two years ago). Otherwise, the engine has responded well and still sounds as smooth as the day of purchase. Gas mileage seems reasonable (but I should formally check it). Although I was originally concerned about the CEL being on, I've just learned to live with it. The shops involved haven't conveyed any urgency so no sense in loosing sleep.

Thank you for sharing your experience on the CEL.
Well I'm going to replace the MAS sensor. Found one new for under $200.00 so I'll see what happens. Maybe I'll get the black tape out and cover the light up if that does not fix it. ML is running OK so far.

For future reference, I'd love the know the source of the new MAS for under $200..... :eek:

MAS Source
 

Drop me an email at smithins@bright.net and I'll give you the source for the MAS and other parts.