91 300E ABS Light Came On, A/C Blower Slowed in Texas
 

1991 300E, 140K with original R12 A/C.

Once in a while I will find some shade and sit in my car eating lunch while listening to the radio. Obviously with the Texas heat I do this with the A/C running.

Today, I was doing the same - idling with A/C on auto and recirculate. I also had the headlights on. Anyway, at some point the ABS light came on and simultaneously the A/C blower slowed as if the battery was really weak. Actually, it seemed as if the A/C was going to shut off altogether, although the engine idle itself was smooth and normal. This seemed to coincide with the auxiliary condensor fan coming on (coolant temp was normal). I let this continue for about 5 seconds, then killed the A/C. Immediately the ABS light went out. About 30 seconds later I tried the A/C again, and within 5 seconds the ABS light came on and the blower slowed again, so I turned off the A/C.

I put the car in gear and started driving around, and turned the A/C on again. I ended up driving about 20 minutes with no problem whatsoever. This seems to have occurred only while idling with a heavy load on the alternator (a/c, radio, headlights, aux condensor fan).

I have done a search and everyone seems to think OVP is at fault every time the ABS light comes on. Is this my problem? It seems more like my battery or alternator output was weak since the problem went away while driving. Also, while the problem was occurring, the car idled smoothly and did not stumble.

Any thoughts? Should I plan on cleaning or replacing the OVP soon?

I do not know of a relationship between the appearance of the ABS light and the blower slowing down at the same time.

Perhaps someone else can draw a relationship based on knowledge.

If you believe what you read here, appearance of an ABS light on an older M103 motor is usually indicative of a faulty OVP. This device among other things, powers up the idle controller, but you say your idle is fine?

I would at the least remove it and give it the shake test. If you hear anything rattling around, replace it. Others will tell you to open it up and solder whatever has come loose or repair a broken path. One tech who used to respond here(the one who started this site) once said in a thread that the OVP was not repairable. Who knows?

I would at the very least check out the OVP.

My 2 cents.

The suspect is a low voltage condition.

Check alt output as you may have a v/reg starting to go .
I would also put a healthy overnight charge on the battery [ seperate charger]and then do a bat. draw test to verify condition..

Thanks for the input guys. Yes, it is a bit baffling to me. I have read about a million times that the appearance of the ABS light is related to the OVP relay, but that said problem would produce an unmistakably rough idle or other driveability issues in almost all cases. That said, although I too suspected a low voltage problem (due to the excessive load on the battery and charging system at the time), my charging indicator light did not come on. I will check tomorrow to be sure that it actually works (lights up at ignition with no crank).

For the balance of the day, the problem did not resurface. It seems mostly to have been tied to the heavy load on the electrical system while idling. I have about a 45 minute drive home from the office, and it was smooth sailing all the way.

I will continue to monitor for this problem. If it resurfaces, I will proceed with your suggestions of checking the OVP and/or battery/charging system as I too suspect one of these is the culprit.

Thanks again!

Arthur works on these cars for a living, so his advise should be considered.

If the voltage regulator is going out, you can check it 2 ways(in my opinion).

The first is to remove it and look at the brushes. Here's a photo of your VR:

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1EQ0PTV2S1KQ0KZE7P&year=1991&make=MB&model=300-E-002&category=F&part=Voltage+Regulator

The brushes are 1/2 inch long when brand new. If they are the issue, then their length will be much less. These pop out the back of the alternator. 2 phillips screws hold them in. Very easy to get in & out. On your car it helps to elevate the front end in order to gain access. Ramps can be useful. There may be a large shroud underneath that must also be removed. 8mm socket gets the screws off.

Another approach is to connect a voltage ohm meter(VOM) to the battery. Set it to the 20 DC scale. Red lead to + battery terminal; black lead to - battery terminal, then start the car.

In my case when the motor is cold, I see 14.20 - 14.30, but my alt was replace about 1.5 yrs. ago. Before doing that, I would see 13.95 - 14.05 on a cold motor.

Once the engine warms up, the alt. output will diminish some and you won't see the voltages just listed. I now see 13.80 - 13.90 once warm. Before replacing the alt., it was getting down to 13.30 - 13.40 when warm.

If the brushes are really worn, I'd suspect that you'd see a low reading on the VOM.

My 2 cents.

when something similar started happening to me.... you could only see the "alternator idiot light" at night.... it was very faint..

new voltage regulator...problem solved.

Well it did it again a couple days in a row. ABS light came on, A/C blower slowed. Again, this was while idling with the A/C, headlights, and stereo on. As soon as it happened, I killed the A/C and the light cancelled out again. Idle never changed.

I hooked up my VOM but because it's analog I can't read down to tenths of a volt, otherwise the numbers "seemed" to be within spec. So with my limited abilities it would seem that the alternator or voltage regulator are OK.

Here's a new symptom: Yesterday I was doing some work on the car (wiring new stereo) and had the door open for about an hour with the dome light on. After the new stereo was wired up, I sat and "tested" it at high volume for maybe another 20 minutes while I cleaned up my tools. When I got back in the car to start it, it cranked R - E - A - L - L - Y slowly before starting, as if the battery was almost dead.

It would seem to me that the battery is shot, or at least not holding a charge, but I know this can sometimes just be the byproduct of undercharging. I'm tempted to replace the battery and see if the problem goes away, but I'm not in the habit of throwing parts at a problem.

Maybe what I really need is a new digital VOM?

Any other ideas anyone?

there are places that will do a battery test for free or for next to nothing.

Sears comes to mind. Although both of my Mercedes have Interstate batteries in them.

Our Expedition uses a Die Hard. The last one held up just short of 5 years. OEM lasted two.

I've only owned this car about a year and the battery is not original, but none of the little prorate stickers (month/year) has been removed so I have no idea how long it has been in there. It is some weird brand I've never heard of... Again, without a digital VOM it appears the battery is the culprit. I'm thinking of putting a trickle charge on it overnight and then taking it in for a load test as you suggested.

I wanted to replace the voltage regulator brushes on the alternator, but I don't see them available on FastLane. Can anyone else suggest a place to get them?

benzbin.com probably high 20's

*************** lower 20's

dealer yikes, maybe 40 dollars

I am sure fastlane has them, too...

I would unscrew the existing voltage regulator and take a peak at it... I once had one that one of the two brushes for very funny with a nub on it... so after awhile the nub was the only thing making contact.

I had another on the shelf, so I replaced it... I probably should file down the nub and throw the old one back in to see if it works.

I always have a spare ovp, regulator, a/c relay, and fuel pump relay on hand...of course I am caring for two 124's


fastlane link:

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1G50WIGFX1KY10ITSH&year=1991&make=MB&model=300-E-002&category=All&part=Voltage+Regulator

cost at fastlane is either 24 or 33, i think

OK, I saw that, but that's the VR. I thought you meant you replaced just the brushes themselves, and not the entire VR.

Update, I parked the car and it wouldn't crank the next day, battery was completely dead. I replaced the battery, and the problem did not reappear. Then, just yesterday, I replaced the voltage regulator for good measure (brushes were worn pretty low when I removed the old one). So I think I should be good for a long long time.

BTW, Fastlane somehow got me my parts (ordered the correct H9DC0 plugs too) very very quickly. I paid for UPS ground but got the parts in 2 days. Impressive!

I went with the cheaper ($23) voltage regulator and will report if there are any problems. So far so good!

FastLane subscribes to the World Parts distribution system. Just about all of the WEB parts providers get their parts from World Parts. That's why the selection menus on all of these sites look more or less the same.

World Parts has distribution facilities across the country. One is in Farmers Branch, just north of the I-35/635 intersection in north Dallas. Your parts likely came from there.

Yes, they came from Farmers Branch. Fast service, what can I say. I've always been leery of ordering parts online, but so far in 2 or 3 transactions with Fastlane everything has worked out well.