My CEL is on and I believe the cause is a bad AMM. When I install the new one, if the problem is corrected will the CEL reset itself or should I do a battery disconnect and see if the CEL comes on again?

Thanks

I don't know the answer to your question but was wondering how you determined the AMM was the problem?

Thanks, Dan

I had the codes read (I honestly forget what they were) but I was informed it pointed to AMM/O2 sensor. I also had a couple of misfire codes. I changed the spark plug connectors - short money and all of my hesitation went away. after a couple of months the CEL reappeared and like I said I was told it pointed to AMM/O2 sensor. Nobody could tell me a surefire way to verify it was the AMM but I always use the rule of thumb that if the choice is between 2 parts and the dealer sells 5 x as many of one than the other I roll the dice. Example when I called the dealer yesterday he told me he had sold 5 AMM's since Friday. I found a site where I could buy it for 50% of dealer cost ($256.00) and figure the diagnostic charges alone would be $100+ so if I am wrong I am out $150 but still have a new part that seems to fail regularly and effect dramatically how the car runs. I'll post the results in afew days once I receive it.

Do you have the info on the site with the discounted pricing?

Tim

In this particular instance I think I just got lucky with the price. I usually use Fast Lane for most of my parts, they too are way below dealer. I will wait to see if parts are delivered on time and correct before giving anyone free advertising.

On my 2000 E320. after replacing mass air meter, the CEL went off after driving vehicle twenty or so times. I suspect codes are stored in memory and may need to be cleared using dealer software. If so, that can be done next time at dealer.

Hi Guys,
Please forgive a lengthy post with lots of questions but I'm really desperate for answers as you wiill see.

I live in Australia and 2nd owner of a 1997 C200 that has 88,000 miles (140,000 km). I've done about half of that.

Now the car won't accelerate until the engine temp guage is halfway up, and until then it is practically undrivable. When the engine is warmed up basic driving is almost normal but it still lacks responsiveness to rapid acceleration, sometimes misfirng in the process. I realise a possible cause is the AMM and I've searched the forum to become acquainted with most of the issues.

The car has just undergone a routine service and I asked the MB dealer to check it. He says it is "probably" the AMM and the cost of the part is equivalent $730 USD, and another $70 USD for fitting. I didn't go ahead with the replacement and after the routine service the car is still the same. I have since found out that I can get the AMM from the local parts distributor at retail price $380 USD, and I accept that this is reasonable for my part of the world. I may be able to do even better somewhere else.

The MB dealer didn't reveal the codes he obtained, and I'm not sure if design rules here require OBDII or whether he used the MB service computer.

OK!, ... now for the questions:

1. Is this likely to be the AMM or could it be something else such as O2 sensor?

2. Is there some way I can absolutely confirm it is AMM before I purchase a new one?

3. If I replace the AMM myself, how do I release the electrical connector since it is difficult to separate and I don't want to break it?

4. If the AMM is the culprit and I replace it, will normal performace be returned fairly quickly without having to reset the codes?

For future reference:
A. Does the Australian C200 have OBDII?
B. Which interface standard does it use?
C. Where can I get a suitable do-it-yourself diagnostic scanner tool?

Any help will be most appreciated.

ClassicGuy

You can clear the CEL by disconnecting the battery for about 20 minutes. But make sure you have the radio code and you may have to reset the power windows. The windows part is in the owners manual. You can just replace the AMM and if that fixed the problem, I think the check engine light will go out after about 40 or so drive cycles. You know, cold start, everyday highway and city driving , acceleration, deceleration, then coolant cooldown to under 100 degrees F. to start another cycle. I could be wrong, but I think that is what it takes, and disconnecting the battery gives immediate gratification. Plus clearing the ECU sets the computer's long and short fuel trims to default. After I changed the AMM I disconnected the battery, and the CEL has been out for 2 months. It took 2 days for all the I/M monitors to go ready, but they all did and I smogged here in California no problem.

fredfisher is right: 20-40 key cycles will reset the CEL, but why not just go to AutoZone and have them use their OBSII to read the codes, then reset the light? When I replaced my AMM (it unplugs simply), it threw a lot of random misfire codes, which was expected (noobs should really search the forums for CEL, AMM, MAS, MAF, as there is a new thread every week or so, and a ton of good info buried in the old threads. just look at posts from blackmercedes for some great air filter advice that will save your AMM before it goes). FYI, you can often find an AMM on ebay cheap (I've paid $40-$50), but you never really know how much life it has left.

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2002 C230 Coupe + 2003 C320 4Matic Sport
http://img.photobucket.com/albums/v1.../sigpic5-2.jpg

When your MAF goes bad the long term fuel trim will usually be out on the high side. Changing the MAF will bring it back in, which should over time cause the light to go out--assuming there are no more codes.

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Lenny

There are only three sports: bullfighting, motor racing and mountaineering; all the rest are merely games. --Ernest Hemingway

'10 GL550/'04 BMW 545/'99 BMW 323/'98 ML320/'87 VW GTI (race)

That may answer my next question. I checked the codes and got a P0170 = Fuel Trim Bank 1, cleared the codes and installed the new AMM. I can see differences in acceleration and shifting but when I really stepped on it I got a couple of "pops" after the 3rd time CEL light came back on and engine was running rough. Could that be because the trim was on the high side and if so will it correct itself after a few cycles?

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1997 C280 Sport

Can't say for sure, but I suspect something else is wrong. Recheck the codes; the "pops" are kind of disconcerting.

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Lenny

There are only three sports: bullfighting, motor racing and mountaineering; all the rest are merely games. --Ernest Hemingway

'10 GL550/'04 BMW 545/'99 BMW 323/'98 ML320/'87 VW GTI (race)

Thanks Lenny,

I did recheck the codes and had a misfire code on cylinder 6. Changed the plugs and the car is running fantastic! Tons of pep, tranny shifting great several long rides and no CEL.

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1997 C280 Sport