Hi Guys Back again I thought the problem was over .
I put a 10 amp fuse in k-4o relay It worked for about 20 miles. Then It started again with the warning light and loss of power. Do I need to buy a new one or put a 15 amp fuse in. Does anyone know what is on that 10 amp fuse? I have a old k-40 relay that was giving me problems but not as bad as this one is giving me now. How do you check these relays? Any suggestions would be appreciated.Thanks Greg

So was the fuse blown again? The K-40 relay is usually checked by replacing it with a known good one. However, the problem may be external to K-40. If a fuse is blowing, something is causing it.
[edit]
The following loads connect to circuit 87, which is powered by K40 and that 10 Amp fuse:
B2/5 Hot film MAF sensor
K40 Relay module (HFM-SFI, HFM-LP, ME-SFI, EDC, base function)
Y3/4 Modulator pressure switchover valve (AT/CC)
Y3/5 Upshift delay switchover valve (AT/CC)
Y31/1 EGR valve vacuum transducer
Y31/2 Pressure control flap vacuum transducer
One of these is drawing too much current and blowing the fuse.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Also, K40 also looks at the system voltage I believe (I could be wrong). If it is like the OVP relays of the older cars, it will blow the fuse if the system voltage goes above around 16 volts. Check the voltage at the battery with engine running about 2000 rpm with A/C, lights, etc OFF. If it is above about 14.2 volts, then that may be your problem.

PaulM

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84 500 SEL (307,xxx miles)

Thanks Guys for helping me. I have had this car for 6 yrs never could let it set longer than 3 days or dead battery. Now that I found the short in this 10 amp line how can I find out which of the 6 things is shorting out? Does anyone have a diagram off the electric and vacuum systems for my 96 e300d with pictures? Thanks Greg

So did the fuse blow again?

The only diagrams I know of are those on the FSM DVD "STAR Classic Service Manual Library, Model 210." It is possible that someone has put some of it on line but the electrical part of the manual is partly on the DVD and partly on line, with the DVD software connecting to the Internet and pulling material needed from a Mercedes web site. Running that without a good copy of the DVD would be difficult. There are probably commercial services that offer this information but the subscriptions are no doubt expensive for the home mechanic. If you have a mechanic who will let you look at his subscription you can track down all of the individual circuits.

I'm not terribly happy with the diagrams in the FSM; they're terribly complicated and have multiple links to other diagrams, requiring a lot of chasing back and forth. All of this is of course just a symptom of the increasing level of electronics in cars. As Mercedes made its vehicles more digital I suppose the circuitry gets simpler in some ways and more complicated in other ways.

In the meantime, I recommend finding each of the items in the list of my earlier post #2. Unplug the electrical connections at each one, one at a time, and see if the fuse still blows. You will get codes thrown because of the unplugged item but they can be ignored. The items should all be in the engine compartment. Remember to plug back in all disconnected wires after each test.

Also be sure to confirm that you don't have a charging system over-voltage problem, as PaulM mentioned in his post #3.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

First off, NEVER put a larger fuse into a circuit designed for X amps.

If you've systematically eliminated all possible circuits as a source of the parasitic drain (per Jeremy5848), look to the alternator's diode pack as the culprit of your perpetually dying battery.

If, and that's IF the k-40 acts similarly to the old OVP relays (I'm not fully up to speed on my w210 yet) it's possible that a bad alternator could be throwing a voltage spike and blowing the protection circuit too.

__________________
Current rolling stock:
2001 E55 183,000+ Newest member of the fleet.
2002 E320 83,000 - The "cream-puff"!
1992 500E 217,000+
1995 E300D 412,000+
1998 E300D 155,000+
2001 E320 227,000+
2001 E320 Wagon, 177,000+

Prior MBZ’s:
1952 220 Cab A
1966 300SE
1971 280SE
1973 350SLC (euro)
1980 450SLC
1980 450SLC (#2)
1978 450SLC 5.0
1984 300D ~243,000 & fondly remembered
1993 500E - sorely missed.
1975 VW Scirocco w/ slightly de-tuned Super-Vee engine - Sold after 30+ years.

Jeremy got your message Thanks for your infor. Put old k-40 in the with new fuse so far no problems. The car was cheap when I got it .Wires under the hood cracked some with no insulation probably short is there.( voltage at 14.0 at 2000 rpm ) no problem there. Flap system never worked ( this is my wife around town car ) Ill continue to try to find the short but Im closer now than before . Is it a pain to put in a wiring harness under the hood? Thanks again JEREMY any thing I can do for you just holler Greg

Greg, the other responders have come up with some excellent suggestions. Given the damaged wiring, you could have a simple short circuit. My '96 had a badly damaged transmission wiring harness, which I rebuilt. The engine harnesses are expensive and take time to R&R but not rocket science just common sense. I wouldn't throw money into new K40 etc. until you have fixed the wiring.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Most of the connectors can be reused but they are fairly inexpensive any ways. Rebuilding a wiring harness once removed is not to difficult but is time consuming just do one wire at a time put some nails in a board to help keep the original below the new harness you build up. Try tagging your wires by original colors at least on each end to help with future repairs.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

Thanks Guys for the help . Ill keep you updated on my car
thanks again

greg