Elkidmino

Hey guys, have a bit of pickle that I'd like to run by you before I start diving deep. 95 C36 AMG, 166K, stock except headunit, amp and sub. I bought the car out of Atlanta 2 years ago from a MB tech and he mentioned the car had a new alternator, other than that, nothing has been touched.

I was out Friday night doing some drifting in the snow and noticed on the way home that the whine emitted from the stereo system had changed tone, the wiper had slowed and the lights seemed dim. The whine has been present for two years, follows the RPM and as best as I can tell is due to a group loop problem which is common on these cars with an aftermarket radio is installed (switched key and 12V+ wires). The whine is not the problem, but it makes a good audible detector of this current draw.

Anyway, yesterday I drove to work with the new, lower whine in the stereo and didn't think much of it. After work, fired up the car and it seemed crank slower. Then I noticed the windshield wiper was again, running slow. Stopped at Advanced Auto for some antifreeze and the car wouldn't restart. A half crank and nothing. Had AA run a battery check and the check machine wouldn't complete because there was too much draw on the system. We finally got it to finish and it said the battery was good but it was at 11.47V & 273CCA, should have been 775CCA. Ask them for a jumper pack, we put it on, hit the key and it fired right up.

Now this is where I start noticing the draw is intermittent. On my way home from AA, the normal whine was back in the stereo and the lights were bright. Every once in a while the tone would change and the the car would dim, while driving, no other inputs on the vehicle like acceleration, turning, braking, etc seemed to affect it. Then after about 20 seconds, it would go back to being fine. I also noted that if I sat at a light for more than 15 seconds, it would go dim again.

The change is very sudden, almost like a relay is kicking on for fans, or a pump or something. The battery doesn't drain unless the car was shut-off in the "draining" condition while it was running. Sometimes it'll undo itself when I shut the car off, other times it won't.

Questions:
-Does the coolant pump on the passenger side frame rail run while the car is running? Or after?
-Is there a check on the electric fan relay I can perform?
-What else runs intermittently while the vehicle is running?
-What does the SRS control? And what is it related to? Is there a relay?
-What are common parts that cause a parasitic current draw?

I'm going to keep this thread updated as I find things, but I'm looking for suggestions on where to start.

Thanks,

Dave

503C43 ////AMG

It almost sounds like you have a seat control module problem but I am unsure if that would cause the same symptoms as your 1995 C36 is pre canbus.

I say this as you are asking about SRS which I can only assume you have the SRS light on

Check this thread out (for W203 but still sounds similar to your problem):
https://mbworld.org/forums/mercedes-...g-battery.html

503C43 ////AMG

If you want to try to isolate it, you can hook up your voltmeter to read amps and put it inline on your battery connection. You should see how much current the faulty system is drawing. Then you can pull fuses one by one while watching the current on the meter and when you hit the system that has the fault, you will notice a significant difference in the current draw

Super B

You know when the EGR air pump kicks on that might be the draw and dimming in the lights your seeing at the stop lights. You'll notice the pump whine right after you start your car or you'll hear it kick on at stop lights. I know you tested the battery with their tester at AA but how old is that battery? When the car is running what kind of voltage are you getting at the battery?

ECTurboGSX

Most multimeters can't take more than 10 Amps inline, so I'd be careful of using it with the ignition in the on position, but that can be useful for detecting parasitic losses with the ignition off. The most useful thing you could have is a wiring diagram. You then isolate specific areas (by disconnecting or pulling the fuse) of the circuit to see if they are behaving as they should. I haven't had any electrical issues on my C43, so I unfortunately don't have any good information to share. I did recently have to chase a gremlin on my bike, so just remember to breathe and stay calm, it will be frustrating.

Elkidmino

Today's update: Took the car back to the parts store and had them run a test on the battery and alternator while in the car. The car was in it's "draining" state until I got to the parts store and then stopped when I pulled in. The sequence for the test required things like high beams, all accessories on, etc. and it passed without problems, no matter how many times I turned the car on and off. It's staying pretty elusive haha. Last night I drove home from work around 9:30p, lights on, "draining" condition was on, blower motor on level 2 and about halfway home the ABS and ASR light came on at the same time. As soon as I shut the blower off, they went out, I have to be sitting at around 10-11 volts for that to happen I would imagine. I'm on the hunt for a voltmeter that plugs into the cigarette lighter so I can monitor the voltage.

So far the only inputs that seems to affect it are drive time and maybe a bumpy road or right-hand corners. Can't get it to shut-off consistently though, it does it on it's own. Turning on/off seat warmers, fans, lights, blower motor, rear defroster (things that would normally draw alot of current) do not have an affect on it.

504C43: I mention the SRS light because it stays on for about 30 seconds after I start the car, everytime, and then goes out. The one time the car was in it's "draining" condition, I turned the key to the ON position and that was the only warning light that DIDN'T light up for once. It has since returned to normal operation during "non-draining" conditions. I read through that thread and am keeping it in the back of my mind. Once I get some time to start poking through fuses I'll let you know what happens. It's been 19-24F and snowy in MI the last week so it's too ****ty out to spend extended amounts of time outside.

Super B: Thank you for the heads up on the EGR pump! I always wondered what caused that draw. Any more info on how it functions with the cat and EGR system? If I temporarily unhook it for a drive, I shouldn't clog the cat right?

Eric: This draw seems higher than 10Amps since it really dims the lights. I've had cars with bad alternators or poor electrical systems, 80 Elco, 89 Conquest and this one is acting very similar all of the sudden. I'll try to keep my head about me on this one lol.

I read about the magnetic field in the alternator and it's affect on the rectifier and voltage regulator in the housing. I'm wondering if the diode is on it's way out and the temperature of the motor is affecting it. The problem does seem to stop once the car is good and warm. FYI, the front fans are still disconnected as an isolation technique.

Thanks for the replies and support. Will keep at it.

Super B

Hey no problem, but I should apologize, the term EGR pump is wrong. The correct term is just air pump ( some call it smog pump ) as it is part AIS (air injection system) here is a pretty good link about it an when it comes on. http://bayhas.com/mercedes/r129/cont...issioncont.htm

The idea behind it is to inject air into the exhaust system at the hottest point to give oxygen to the exacaping gasses. By adding oxygen this allows further combustion of the remaining fuel. This adds heat into the cats to help burn the hydrocarbons and also keep the cats burnt clean. As far as testing goes. Yeah I can't see how your going to hurt anything by pulling the plug on the pump but might throw some emission codes (maybe a merc tech could chime in on that one) probably not the best on the cats long term but for testing don't really see how your going to hurt anything.

But to be honest I really don't think your problem is there. I'm betting it will turn out related to the charging system. To check the voltage of the battery while the car is runnin just press and hold the REST button on the climate control, once the display starts flashing use the fan plus to scroll to output line 24. It will display battery voltage. The refresh is slow but works.

Elkidmino

I just came on here tonight to refresh my memory on how to do that and you're already one step ahead of me. Thanks!!

Elkidmino

It looks like I've tracked it down to the voltage regulator. One of the brushes is in bad shape. Does anyone know the stock PN for the regulator so I can cross-reference it with a Bosch one? The actual regulator has VR-B201H on it.

ECTurboGSX

You can sign up here for a free year of viewing the MB Electronic Parts Catalog. My year ran out and haven't bothered trying to start a new one yet, or I would look it up for you:

http://epc.startekinfo.com/epc/

503C43 ////AMG

Here are the Bosch and benz part #'s
BOSCH : 0-192-052-008,0-192-052-011,0-192-052-012,0-192-052-013,0-052-014

MERCEDES BENZ : 21541806,21542506,21540606,21545806

Elkidmino

The saga continues. Ordered a new voltage regulator (Bosch PN: 1-197-311-242) and installed it in the car. Battery is at 12.39 volts with everything hooked up, key off. Engine on, it runs at 11.66 volts. No amount of throttle input, to excite the VR, seems to have an effect.

-If I disconnect the alternator and run the car I see 11.75 volts with little change. No warning lights.
-If I hook the alternator back up and run the car, the battery light, ASR, ABS and center "!" indicator are all on and it reads 11.71 volts at the battery.

I noticed the inner brass ring where the brush contacts, closest to the alternator body, looked a little chewed up when I removed the old regulator. I cleaned all the grounds and applied di-electric grease to the new brushes and no change.

Now I'm thinking one of the windings broken in the alternator and causing it not to charge.

How is the ABS/ASR system related to the charging system? Do the lights come on when the car drops below a certain voltage?

Elkidmino

FIXED.

New alternator in and it's charging again. About time.

Onto the miss it developed while sitting.

Elkidmino

Miss fixed too! Bad coil. Added new plugs, wires and coil boots.

Now to fix a fuel leak at the fuel pump. LOL