E300/W210: Battery drain - help!
 

Driving home last week and all of a sudden a 'brake pad wear' warning was displayed on the console-thing - I knew my brakes were in need of a service so I thought that it was not unexpected. What I was not expecting was the slew of BAS/ASR warnings displayed about 5 minutes later. I was only a few miles from home at this point - turning up the street my radio turned off and I was stuck in 3rd gear until I pulled into my garage.

The next morning I tried to start it up but the battery did not have enough juice to turn over the engine - I figured that would explain the weird electrical issues the night before. Since my battery is less than a two years old, I thought this issue was just a bad alternator - but after a installing a rebuilt one there has been no change. The battery voltage while the engine is idling is about 10.5 volts which is obviously not correct.

After reading as many old posts as I could find related to my issues, I have performed the following with no luck:

- Installed rebuilt alternator (as mentioned above)
- Cleaned battery terminals & chassis grounding point
- Disassembled and cleaned power distribution connector (X12/3)
- Disassembled and cleaned grounding poiints in engine compartment

Any help is greatly appreciated!

What's the battery voltage with the engine running at 1500 rpm with the headlights on and the blower running at max?

I have had no issues like these. Sometimes weird electrical issues are attributed to the K40 relay. However, your symptoms do not sound like ones I recall with that issue, but you may wish to look that up and see if anything sounds familiar.

So that is a random guess on my behalf, sorry.

Might actually be the K40 relay
 

check out this thread... mentions low batter symptoms and K40.

http://www.peachparts.com/shopforum/showthread.php?t=166998

http://www.peachparts.com/shopforum/showthread.php?t=147720

main one on K40

http://www.peachparts.com/shopforum/showthread.php?t=198318

Looks worth checking this out.

Battery
 

1984 300d Turbo 146k
Replace Your Battery And Alternator Needs To Be 13.2-14.2 Volts
Autozone $90.00 Plus Core $12.00 Do A Search Battery Drain

Yeah, just because the battery is only 2 years old doesn't mean it is good. One bad cell in 6 can cause low voltage. Have the battery tested, most auto parts stores will test it for free. That will at least either confirm or eliminate this as being responsible.

Thanks for the advice - here's a small update:

- Detached battery terminals and put on a trickle charger all night - this morning, charger was showing about 1-2A @ 13.8V.
- Pulled K40 and checked connectors and PCB - found an odd 'solder bridge' made up of what appeared to be tiny metal flakes (see attached). Cleaned up PCB on K40 and reinstalled.
- Put multi-meter in amps mode and put in series from positive terminal to car positive terminal - was showing about 0.75A. Connected battery to car terminals and checked battery voltage - now showing about 13.4V.
- Car started right up and seems to run great. CCU in diagnostic mode on sensor #24 showed 11.0 - turned on headlights and showed 10.8 - set blower to max and showed 10.7 - increasing engine RPMs did not make reported voltage fluctuate - turned both off and went back to 11.0 - battery voltage checked with multi-meter was 11.5V while idling (I assume the multi-meter is more accurate than diagnostic reported by CCU)
- Turned off ignition and checked battery voltage - showed 12.6V

Not sure what might be happening but I'm going to pickup a new battery later today.

I would be especially concerned about that solder bridge, which could be causing a short. As for your voltage readings they are very much on the low side. I have a Scanguage attached to my vehicle, and when first started, with the lights on, rear defroster, and front defroster activated, and the afterglow process engaged, my voltage measures 11.8 at idle. With the afterglow process completed, my voltage jumps to 13.2 at idle, and 13.5-13.7 at about 40 mph. Good luck with your problem.

I've got an old known good K40 relay. I'll check the bottom of it and see what that area looks like.

There are two alts that were used. Up until prod date 11/97 they were 90A, thereafter 115A. Did you get the correct model?

Did you repalce the regulator too?

The BAS/ASR lights sounds like batt voltage. ECU loses communication and reports system warning on dash.

Those two points are not connected to each other on the back of my relay.

Didnt want to pry it apart to see if they connect on the inside of the PCB. Too many pins to try to get back together.

I did not measure any continuity across the solder bridge but there was some resistance - fairly large (k-Ohms) if I recall. Bridge was easily wiped away with a cloth. I purchased the newer 115A alternator as that is what was original - the regulator is internal to the alternator, correct? I'll have the old one tested just to be sure. Thanks for checking your K40 Terry.

Update: Bought new 'group 49' battery at Sam's - same results (idling voltage remains at ~11V even after 2-3 minutes) - revving the engine does not change reading. Belt is not squealing - I assume it is not slipping since tensioning system spring is not broken. I wondered if the glow plug relay could be 'fused' but not reporting the error code - removed relay and checked for continuity between +12V input pin and all 6 outputs (there was none). I did notice about 9k resistance between ground and each of the 6 outputs - does that sound OK/correct?

From inside the car you would not know the charging voltage is really low - starts right up and there is no indicator light or warning message...

Looks more like arcing to me, the bridge being composed of the tinned copper PCB.

If its been modified by someone, they're an idiot. If you wanted to hardwire something like that then you'd just use wire.

Unless you swapped in your old reg the new alt must come with it atached.

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=25L0RF04Y2B310OCNL&year=1998&make=MB&model=E-300DT-001&category=F&part=Voltage+Regulator

Another update: Cleaned the contacts/terminals on the alternator and coolant circulation pump - disconnected condenser fan (does not work anyway) just in case it is drawing too much current - still only 11V while idling

I think I'll be ordering a new K40 just in case - and to have one as a backup in case it is OK. I am still perplexed by that 'bridge' that was present before I cleaned it away - there was no evidence of any other bridge anywhere else on the board or even any contaminants. Could that be the remains of an undersized wire from a modification by the PO?

Just in case there are any K40 experts out there I've attached a picture of the connections so check if anything is odd or out of place. Notice the spliced wires on the left side of the attached photo - not sure how those got there...

(bump - 'cause I'm commuting with the wife!)

Quick question: does the alternator get its link to ground through the engine? I have not checked the grounding cable(s) from the engine to the chassis yet - a friend of mine at work recommended using some long jumper cables directly from the battery to the alternator just to rule out any potential corrosion issues.

I would be very cautious about using battery cables directly connected to the alternator. If a lead were to slip off, or short out against the alternator casing you can fry the alternator diodes very quickly.

Good point - I'll just attach the negative side only since that is the current path that I fear has excessive resistance.

No luck with the jumpering the ground. I did notice that with the battery connected and the engine off that the voltage between the B+ connector on the alternator and ground is not the same as the battery voltage. It starts out at the battery voltage (~12.5V) but it decays fairly rapidly (around 5 seconds) to about 10.6 volts. As far as I can tell from the wiring diagrams is that the positive terminal from the battery is connected directly to the starter and the alternator - any idea what might be happening? If someone else with a E300D can check the voltage (car not running) between ground and the B+ terminal on the alternator and report back that would help me out tremendously...

scott, where are you getting your voltage reading? From the CCU or voltage meter from a location such as the cigarette lighter?

The voltage readings on the CCU are slightly lower than actual as there are resisters to slightly reduce the voltage going to the unit....

I'm measuring the voltage with a multi-meter directly at the B+ terminal on the back of the alternator (see attached - green circle). The battery voltage at X12/3 on the fender is fine and I put the wire brush to all the terminals just to make sure. I pulled up the carpet on the driver-side to access X4/31 and check the voltages there but it is covered with some sticky felt material for protection - I think it is probably OK since the whole area is very clean and dry. I wire brushed the terminals at the starter (M1 in the diagram) as well as the connection back to X4/31 from underneath the car just to be sure they're OK as well.

Do you know physically where the connection between the starter and the alternator resides (blue square in diagram)? It is not referenced to a connector block so I am assuming that it might be splice within the wiring harness...

I'm thinking about putting some ring terminals on a 6-8ft length of 8AWG copper wire and running from the alternator directly to the X12/3 terminal and see how that works. I cannot seem to find where the splice/connection between the lead to the starter and the alternator so I think this might be the a good test. I'm not sure of the wire gauge from X4/31 to X12/3 so this will only be temporary for debugging purposes. I'll post my results...

Update: Traced alternator output terminal (B+) back to battery - the previously posted electrical diagram is wrong as it does pass through the X12/3 connector. Detached both ends and measured resistance of about 10 M-ohms so it's pretty much toast. During the process, found windshield drainage duct (#53 in attached) totally plugged with debris - it must have been water tight as it was completely composted black! So, water was pooling around these cables every time it rained for quite some time now.

I just soldered some ring terminals on an 8-ft length of 8AWG stranded cable - we'll see how that works in it's place.

You drive your car in the rain!?
 

Well you made me go check mine. Appeared perfectly clean. Good to know. Keep us updated if that clears things up.

Success! Battery is charging properly now with new custom cable from alternator to X12/3 terminal. I'll install a more permanently routed cable with proper friction tape later.

I guess this is a lesson for W210 owners - clean out those drainage ducts right after the fall season!

Dear Scott,
Currently I am repairing my k40, I shall be really grateful if you could please attach a complete view (clear picture/s) of your k40's back circuit board. Right now I can see only middle section of your k40.

Thanks!

Scott last posted on this forum a year ago while selling his car. You might have better luck sending a PM or trying to find an email address.