W201: battery charge warning light weirdness

[gastropodus]

Hello diesel brethren,

You may have noticed that I recently updated my signature to reflect that fact that my W201 (190D) is back on the road. I had gotten the delivery valve seals and injectors replaced, but got stuck on a clutch hydraulic problem (ended up taking it to Burback Motors for repair, which they did competently).

However, it had sat for quite a while , and now that I'm driving it again I have encountered some electrical gremlins that show up primarily as the following: I get in, turn the key to glow, all the proper status lights and glow plug lamps light. Wait the prescribed interval, then engage the starter. Car starts normally. After driving for about 5 to 10 minutes, the engine continues to run, but the light with the battery symbol will come on. Once this happens the turn signals stop working. Sometimes I have noticed that applying the brakes will trigger the condition with the battery charge warning lamp: if I press on the brake the lamp will come on, or if the lamp is already on it will glow more brightly while my foot is on the brake. I'm worried that the brake lights are no longer working when the lamp comes on, but I haven't had a second person with me in the car yet to test whether that is true. If I wait long enough, like 20 minutes or more of driving, the lamp will go out and everything is normal for as long as I care to drive.

Most of the other electrical items of the car continue to work when the battery lamp comes on: I've tested and found the following all work even when the lamp is lit:

- interior light
- windshield wipers
- front headlights and side markers
- the fuel gauge continues to work, though I sometimes see it whipping around like there is an open in the circuit somewhere (I've taken the sender out and cleaned it - though it was clean as a whistle to start with)
- the temperature gauge continues to work normally
- the interior fan works normally
- strangely enough, the emergency flasher will work when the lamp is on, even though the turn signals will not!

So far, here is what I have done to try and correct the problem:

- replaced nearly all the fuses, which were aluminum, with the better copper ones; I still have a couple at the top of the tray left to do (ran out of fuses)
- cleaned and re-tightened the clamps on both battery terminals, as well as the ground cable connection from the battery to frame
- the tech at Burback said that he looked at the alternator brushes, and they were good, though the commutator looked a bit corroded.

I did see some flakiness once with the ignition switch: I went to start it, and the lights all went out until I turned it back to off, and then turned it back on. This happened a couple times, so it seems like the electrical portion of the ignition switch probably needs replacing. Does it seem possible that this could be the main problem?

Other possible causes:

- some other frame ground strap is high impedance, needs to be cleaned and tightened?
- the alternator and/or voltage regulator really is bad, needs to be replaced?
- the turn signal relay is bad? (Where is it?)
- there is corrosion on some of the connections behind the dash?

Any advice on how to tackle this?

Thanks,

Kurt

[layback40]

Undo your earth strap & clean the contact faces.
Unplug the wires going to the alt & clean the pins & plugs.
Clean your battery terminals.

If that does not fix it, remove the reg & check the brushes.

[LNGfish]

Nice write up. I'd take it and have the alternator checked for low voltage. Usually free here and they give U a print out at Advance Auto Parts store. Good luck.

[Bob338]

Grounding cable cleaning and voltage regulator replacement fixed identical problem for me. Don't know which it was as I did them both at same time. Both very simple.

[gastropodus]

Normally I'd say replace voltage regulator and just be done with it. However, I think I recall Mike Burback saying that the VR is integral within the alternator, so basically I'd have to replace the whole thing as a unit.

Bob338, did you have the same "turn signal and brake lights don't work" weirdness? I confirmed today that the brake lights are inoperative when the battery lamp is on.

Thanks for your thoughts,

Kurt

[benedict]

Originally Posted by gastropodus

"turn signal and brake lights don't work" weirdness? I confirmed today that the brake lights are inoperative when the battery lamp is on.

Kurt

That is sounding more and more like your ignition switch or if your car has one, an ignition relay.

The brake circuit doesn't run through any kind of relay (with the exception of an ignition relay) so that should rule out a low voltage to relay related problem. Even if your battery was low on juice due to a charging problem, your brake lights should still work.

A dodgy regulator could give you problems to the turn signal relay if you were passing too much AC or even a high/low voltage could cause the relay to play up but now that you have mentioned the brake lights are out during the gremlin run...

Could also be a high resistance somewhere on a ground but they can be difficult to trace without the use of a multimeter. And you can spend hours shining joints up for nothing.

The brake lights won't work until the ignition is set to 'on' usually:some cars are different of course like my Alfa Romeo but anyone who has had an Alfa will definitely understand the meaning of electrical gremlin!

At this point I would suggest taking it to an auto electrician as LNGfish suggested, because changing out parts, such as ignition switches aren't cheap and might cost you far more than a diagnosis would. They know where to look as it is the usual culprits with each make and model.

If you can measure the voltage on the battery that could further help with a diagnosis from the forum. Measure dc voltage at battery with car off and record, measure dc voltage with car running at idle and record and also set your multimeter to AC and see if there is any voltage; it should just jump around in AC mode but if you do get a voltage reading then your regulator is gone.

Your voltages should be (approx) 12.6 to 12.8 on a healthy fully charged battery under a no load condition with engine off and climb to roughly 13 to 14.5 when engine running and alternator properly functioning on a bosch system. You have to run the car for a few minutes or until the glow plug circuit cuts off as the glow plug circuit draws a considerable amount of juice and will give you a false battery voltage as low as 11.5 sometimes; well it's a true reading at that point in time but will be low.

[Walkenvol]

Originally Posted by layback40

Undo your earth strap & clean the contact faces.
Unplug the wires going to the alt & clean the pins & plugs.
Clean your battery terminals.

If that does not fix it, remove the reg & check the brushes.

I wouldn't do anything until I had completed the above as these are the most common failure points of the charging system along with being relatively easy to complete and the regulator is relatively inexpensive.

Good luck!

[benedict]

Originally Posted by Walkenvol

I wouldn't do anything until I had completed the above as these are the most common failure points of the charging system along with being relatively easy to complete and the regulator is relatively inexpensive.

Good luck!

I agree, process of elimination. Do all the jobs you are capable of doing yourself first. A shop is going to do the same thing but with the $meter ticking over.

[gastropodus]

Well, I changed out the voltage regulator and did a little emery cloth work on the alternator terminals (they were greenish-corroded looking). Took it out for a spin, and did not get the charge light to come on. Turn signals worked throughout the drive, so perhaps if I'm lucky I've fixed it. Then again, yesterday was the first day in quite a while in which it hasn't been raining, so perhaps that is what really affects it.

I'm still puzzled by the link between the charge light and the turn signals. Is it possible that the turn signal relay just won't operate at standard 12 volts, and only operates at the higher charging voltage? Where is the turn signal relay on a 190D, anyway? Is it up under the dash behind the kick panel, I suppose?

Kurt

[gastropodus]

Update: the voltage regulator and emery cloth work on the alternator itself did not fix the problem at all. I've been driving the car up until this weekend, with many dropouts of the electrical system. I finally got the instrument cluster out on Sunday; I originally wanted to see what condition the grounds were in behind the dash.

Well, I got curious about the instrument cluster tonight, so I undid the screws and separated the front bezel from the working portion. This allowed me to inspect the solder joints of the circuit board behind the temperature / fuel / oil gauge portion of the cluster. Lo and behold, I found some cracked (so-called dry) solder joints! Most significantly, one of the cracked joints appears to be the GROUND pin connection on the big circular connector! I took two photos of this particular failed joint, though there are more scattered over the board; if you look closely you can see that the solder blob is actually split into three pieces: one is the pin itself, the second is the resistor connection, and the third is the connection to a trace. Very, very interesting.

It's especially interesting in light of a conversation that I had with Roy this morning. He very generously gave me his time and insight on electrical problems, and one of the things that he said is this: the alternator / battery warning light is actually an integral part of the charging system on a Mercedes (maybe other cars, too). It's part of the excitation that makes the alternator actually function. So it it would not surprise me at all that an instrument cluster with high ground path resistance is going to behave very strangely.

So, tomorrow I'm going to clean up (resolder) circuit connections at work (I'm an electronic engineer - yay, a problem that seems to fall squarely into my area of expertise!). I'm just trying to decide how proactive to be:

- remove all the old solder from each joint, resolder with new solder?
- just heat up and reflow all the joints?
- replace solder on broken joints only?
- or just heat and reflow broken joints?

My theory on this is that Germany was at the forefront of environmentally "green" industrial practices, and that these kind of problematic circuit boards were produced in the period where companies were just switching over to lead-free solder. They probably didn't quite have the solder composition and techniques quite worked out yet, and now 25 years later we're seeing the result.

Kurt