RWDvelocity

Hello all,

This is my very first CEL in this car and I'm wondering if anyone can throw some ideas my way. Car sat for two weeks in the garage and has been taking me all around Maine w/o issue for the last two days. I got home, got out to open garage door, got back in and found the Check Engine Light on.

Idles fine, drives fine, smells fine. The trans. was shifting often on the hills around here (fluid changed 15k miles ago by dealer) but other than it has been business as usual. It has 46k miles and I did put a tank of gas in a few hours before the light came on. I checked the cap and it looked normal but I took it off and replaced it carefully just in case. If it was a loose cap, will the CEL go off on its own?

Thought 2- I go between Massachusetts and Maine often with 93 octane in MA but only 91 in ME. Could the octane changes cause computer confusion? I have to drive back this Sunday and I'm scared to with the CEL on. I appreciate any thoughts. CEL lights make weekends seem so long (in a bad way).

BJonesFL

If you have a post '96 model, you can have the OBDII CEL codes read FREE at AutoZone, Advance AutoParts, etc. This will give you a place to start in diagnosing why you're lights on.

RWDvelocity

Hi, thank you. I should have mentioned in my original post that its a 2001. That's a good idea about AutoZone. I will check for one in my area.

SRHsl600

OBDII read can save in all dimensions, Luck you!

RWDvelocity

Looks like I have to get the OBDII codes read- the CEL went out on its own but then came back after filling up the tank again. I wonder if my gas cap is no longer sealing properly. Has anyone with a later model 129 had that issue? I have also noticed that I am "topping off" the tank when I refill. I know its expressly verboten but some of the pumps around here click off before the tank is remotely full.

SRH- to diagnose a CEL or the like in a pre-OBD 129, do you have to take it in to the dealer or is there an at home reader for it?

SRHsl600

I go to my Indy, I am certain his electronics can be purchased. OBD I and the analogy reader were connected in about the same location. I watched the screen read out, but did not place the connections, so my expertise is infantile.
The Mercedes forums I read have many "home built" systems mentioned. Good luck with your search. My Indy uses these readers on all the cars he services, Benz, Saab, Volvo, Bentley, Rolls, Porsche, VW, and even my Jag!

RWDvelocity

Update:
The light came back on after a few weeks and I stopped by an auto store to read the code. I don't recall the number but it was Fuel Trim Error Bank 1&2. The garage suggested that the air filters might be dirty (original from 2001 with 46k miles). Having read a few posts about dealership citing a failed MAF as the culprit, I was wondering what people around here think.

When the MAF failed in my Volvo, it was very noticeable. If the CEL never came on, I wouldn't know there was a problem in the SL, which makes me think its dirty filters. Any thoughts?

BJonesFL

If the air filters have never been changed, absolutely replace them. Very inexpensive for the pair and you'll notice an increase in gas mileage almost immediately

I got the same fuel trim DTCode several years ago, and was told that I needed to replace the MAF for $150 or so. 2nd opinion from my now current Indy tech was to remove the MAF Assembly (takes all of 3 minutes to remove) remove the internal sensor (remove 2 torx tamper resistant screws and the sensor can be removed) Spray the wire side of the sensor (you'll know what I mean when you see it) liberally with CRC brand MAF Cleaner (any auto parts store should have it I got mine at Pep Boys) Let the sensor dry for a few minutes, reassemble and reinstall the MAF. The first start following this, the engine's computer will train itself using the new readings from the MAF, and the first 5 minutes or so, the engine may fell a bit rough running. This goes away and the fuel-air mix is back in spec and your engine will feel like a new one. Good Luck

RWDvelocity

BJonesFL, thank you very much for that detailed info. It sounds like something I could do myself. Somehow, replacing the air filters never happened. I like my service department but they won't check specific areas without committing me to some expensive "list" of things that are obviously fine (battery, tires, wiper fluid). Maybe that's how it happened.

I'm glad there is something left on these cars that an owner can do on their own.

BJonesFL

Your welcome.

As long as you're going to change the 2 engine filters (found under the engine cover-remove cover flip over and you'll see them. Pick up a set of tamper resistant torx screwdrivers, our cars are loaded with these screwheads You'll need them for the MAF and to R&R the engine air filters.

If I were you and found that these air filters had never been changed, you might as well get a new cabin air filter. It sits in the rectangular black box, roughly 5" x 14" directly under the windshield wiper motor. Installation is easy and pretty intuitive, but if you need assistance, just post.

WhiteSL500

I've also heard of an O2 sensor causing a CEL In a 95 C280. No symptoms at all. Car drove perfect still had a CEL. Don't know if that has anything to do with the code though.

RWDvelocity

Thanks, WhiteSL500. I'm at the dealership now and its the MAF. I'm so busy at the moment that I don't have time to try BJones's suggestion and $600 for a new MAF feels like theft. Is that typical deaer markup (plus the 'programming')?

SRHsl600

The price I paid for the MAF was about $280 each ( 2007 ). The labor was part of everything else being modernized. I have found the Indy, that was reluctant to sell me the parts, was correct, because the MAF can be set off with very small particles and Kansas air has lots of stuff blowing ( Wizard of Oz et al )

RWDvelocity

My receipt states mine was $414 (must have been flown over first class by Hanz & Franz), plus $177 for labor. I would have loved to have done this repair myself, as it seems many have.

What makes me feel better about not having cleaned the old one (at least what I keep telling myself) is that the CEL would come on and off, possibly indicating that the MAF was truly gone not just dirty. The printout also says, "Code Self Adaption At Limit, Check For Vac Leaks and Air Intake Leaks". Thankfully, those leaks weren't found.

BJonesFL- I did leave the passenger air filter as a job for me! And you're right, I did notice a change after the engine filter replacement. She runs noticeably faster (peppier) and the exhaust note sounds clearer. The tamper resistant screws- were they trying to keep those pesky owners away from their cash cow?

BJonesFL

This type of screwhead is thought by some to be better than a philips, for example, as it provides one addiditona spline to increase 'bite'. A full set of the most common sizes runs around $ 30 for a decent quality set. Enjoy your ride-

RWDvelocity

Hi BJonesFL,

There is an indie shop very close to me that comes highly regarded by the MB Classic Center in Irvine, CA. I should have gone to them but this particular dealership was near me at the time I found out about the codes. Next time, thought, I'll skip the dealer. I'd rather support good indie shops.

I asked for the parts and was given a nice box that contained the new parts, however only the old filters were in them. I guess they didn't hear, remember, or feel like giving me the MAF as well and I should have checked.

Thank you for the information on the tamper resistant screws and how to replace the cabin air filter. I'll breathe easy knowing I did that one myself.