W126 : Kansas City Breakdown

Update from the road: My son said that last time it died after a restart, it would not start back up and the battery went completely dead after sitting 30mins with hazard flashers on.

.................Scott

I would check a couple of things...

1. Fuel Pump Relay... it is the biggest black relay in the fuse box. If the date stamped on the side is same as the year of the car... definitely bad.

1. Overload relay fuse... in fuse box with red fuse on it... check if fuse is okay... check date if possible.

2. Battery age? If over 4 years old... time for another one... Autozone is the place to get it.

1. Double check the charging system... Autozone will help too along with dealer.

Good luck!

Something is draining off electrical power.

Some possibilities:

Any modifications to the car? Like an after market stereo etc.? If so, drive with it OFF, if only to eliminate it as a suspect.

How old is the battery? It's a suspect if older than 4 years.

Did dealer test the alternator or just say it seems OK? Alternator has (replaceable) diodes that die after many years use.

Car ever wrecked? A pinched wire at crash site could be shorting.

You're a good Dad.

Thanks T.G. and Tiger. We had it towed back to KC last night so I am going to send your ideas along to be checked by the dealer.

And, T.G. your questions are relevant. There are aftermarket amps in (very low power and been in for many years though - could be defective), battery is at least 4yrs old and, many years ago, the left front corner was crunched. I supposed the dealer could check for current draw while the stereo and lights, etc are turned on?

Dealer said they tested battery and alternator - hence our decision to replace cracked belt and weak tensioner as possibilities - but will ask to get them tested again along with test for current draw.

I appreciate the responses! ...........Scott

Update from KC Mercedes Dealer Service dept: Got the 300SE into the service dept first thing this morning. My son gave the tech the list of possible causes you folks sent along. Tech just came back and said they found an internal short in battery.

He is re-testing alternator in all 3 stages (not sure what they mean by "stages"). We're going to have them replace voltage regulator too - and then a road test with everything electrical running.

............Scott

Second update from KC Mercedes Dealer Service dept: Tech syas alternator is spiking. HOWEVER: He said regulator is not seperately replaceable. I sent my son ack to question this based on the info I got from the MB group here.

So, could it be this model (91 300se) has an internal regulator that is not easily replaced?

............Scott

I'll defer to the experts on this group, but a quick look at benzbin shows a voltage regulator (F4010-108169) seperate from the alternator (F4000-10024).

Josh

Thanks for part numbers Josh.

Third update from dealer service dept: We checked back and the tech says regulator is indeed external but he determined it is a diode problem - it is the diodes that are inside. So we will go with a new alternator too, to be on safe side.

They are putting it through some sort of load test.

Good news is, in view of great inconvienence, dealer has offered him parts cost only and no labor charge because they missed this first time!

I checked the Performanceproducts.com paper parts catalog and see NO separate voltage regulator. Their alternator is remanufactured by Bosch and they sell it for $292.

Lucky that the KC dealer is open on Saturday.

That IS good news - considering this is a one time customer who has no alternatives.

Decent.

Not bad. Hope they paid for the 100 mile tow as well - but maybe that's asking too much.

He's lucky to have broken down (a) in KC - I spent a year out there - rather than the middle of nowhere and (b) in a city that he can get MB service on a weekend.

Hopefully the car won't have any other issues for the rest of his trip.

Josh

Indeed, it could have been a worse predicament and dealer has been excellent so far. The two 100 mile tows were on AAA (he has the AAA Plus service that provides 100 miles to a facility of his choice). AAA was very responsive - no complaints.

They should be finished with the car in about an hour - once he makes it more than a charged battery worth of miles down I-70, he should be OK. I suggested he take a loop around KC first, with all manner of electrics running :^)

I'll post the results.

Scott

That is good news... just an alternator and battery. Just replacing the regulator would yield a couple more years of service... about two more time is all you can get out of it unless you totally rebuild that alternator.

Dealer don't carry those voltage regulator alone... they rather make money on the whole thing... that is why they don't stock em. Aftermarket is available everywhere.

I had similar symptoms with a GM car recently. The mechanic said it was not the alternator.

It was the alternator.

I wouldn't rule it out yet.

They do that when voltage drops from 12 to 0 volts. At 2, 5, 8 volte they do unpredictable things. The lights dim.

If the battery tests ok (> 12V) it's almost certainly a bad ground.

Pull the two ground straps off, clean them to within an inch of their lives, and put them back on.

If that does't fix it, pull all nonessential fuses. You can live without a horn if it'll get you home. It may be some haywire circuit somplace.

Sounds ike a flakey ground to me though.

It looks like the alternator and battery replacement did the trick - the 300SE is back on the road - 350 miles from KC with no problems.

Two thumbs up for Jay Wolfe Mercedes in Kansas City - it is good to know there are still shops that will stand behind their work and treat you fairly.

Thanks to all of you on the alt.auto.mercedes group - you really came through!

Scott

Alternator and a battery? just FYI, the regulator (on the alternator) is usually what fails. $18 and two 10mm nuts replaces it by crawling unde the front of the car, it doesn't need to be in the air. In a pinch you can buy two $1 brushes from an alterenator/starter place and repair the old regulator.

I realize this doesn't help you, but it may help the next guy.

A $5 voltage meter will diagnose the battery and alternator.