1996 E300D W210 Random Electrical problems
 

Random Electrical problems

1996 E300D W210 77k
When the problem occurs: Voltage at the cigarette lighter is 7.6v
When the problem occurs the following things do not work:
wipers
garage door opener
power windows
cruise control

The following things do still work:
It starts and runs
head lights
hvac
power seats
radio ( but, if you try to use one of the affected functions, it will cut out until you release the affected functions button )

When you turn the key to the first position:
if the SLS light is bright, then everything is fine
if the SLS light is weak, then you have some or all of the symptoms

if the SLS light is weak and I turn on any of the affected functions, the light will get weaker or go out
if I turn on the wipers the SLS light will flash from it's weak condition to weaker and the K1 relay will click
sometimes when the SLS light is in it's weak condition and I turn on the wipers, they will come on and the SLS light will change to it's normal brightness

In the last month the car has "turned off" while driving twice. All the dash lights come on, the motor quits. Stop, put it in park, restart, and no problems the rest of that trip.

All fuses for the affected functions tested good, and everything does work some of the time.

Has anyone experienced this problem on this model car and solved it?

Thanks,
Greg

I would check all fuses, both in the engine bay, on the left side of the dashboard, and under the rear seat. Just don't look at them, remove, test, clean and replace if still good. I had a similar issue with the wiper, washer not working, and it was intermittent. Looked at the fuse, and it was not blown, but upon further inspection, it turned out that the fuse holder contacts were oxidized, and would cause the fuse to make intermittent contact. Used electrical contact cleaner, and all is well. I am not sure if the K-40 relay would cause any of the issues you have, but that is easy and cheap to replace. Good luck!!

Look at the main power feeds, these should be the smaller wires at the positive battery terminal.

You might have a ground coming apart as well. Sometimes many grounds are attached to a common bolt, if the body side is corroded, some systems back feed into others

The fuses all test good.
Everything is clean at the battery terminals.

When it occurs, I get 7volts on all the affected circuits. Same voltage every time.

When a load is applied,
sometimes it will cause the circuits to come to full voltage,
sometimes it will cause the circuits to drop out completely.

Repeatedly cycling the ignition key off and on will eventually result in full power to the circuits.

What relay, if failing, would cause a low voltage condition on some of the car's circuits ?

The K40 module in your car is related to (descended from?) the OVP relay in the 124 and similar models. It's possible that it might cause a failure of the kind you describe. (K40 failure is usually associated with an engine that stalls because the IP is powered through K40.) My '96 E300 has not experienced your problem and I don't know what else to suggest. The price of a new K40 is about $100.

Jeremy

I re-soldered the K-40 circuit board before I started this thread.
Since I have 2 - 96's, I will swap the K-40 relays and see if the problem follows.

I'd replace the K40 relay. Its bad, or, you have an unrelated bad oring behind the SOV causing the stalling.

Swapped the K-40 relay. No change.

All the fuses are good.
The battery is good.
All the things that don't work when the problem occurs, do work when the problem doesn't. All or nothing, they all work, or they all do not work.
The car always starts and runs.
The lights and signals always work.

There is something that is intermittently causing the voltage to the affected items to be limited to 7volts. When this happens, turning the key off and on repeatedly will eventually hit a good, full voltage, situation. Some times it is after one try, sometimes it is many.

Can you attach a voltmeter to one of the affected circuits so that you can monitor it at all times while driving? It would be interesting to know whether the voltage changes significantly at any time (other than preglow and cranking) and whether the problem always occurs with the voltage change and never without it. You have written that the voltage is always low when the problem occurs; I don't know if the problem occurs and then you measure the voltage.

Have you checked and/or replaced the alternator, or at least the regulator with its brushes? At only 77K miles the brushes should not be worn out but I'm running out of things to suggest.

I assume you have pulled everything in the electrical box on the passenger side of the engine compartment and checked for good clean contacts. There are a lot of electrical gadgets that talk to other gadgets in ways that I do not understand, via the CAN bus.

The only other thing I can think of is to go through the car's collection of ground points one by one, removing the hardware that bolts the terminals to the chassis and cleaning each one. The FSM should have a page or pages showing where all the grounds are. With only 77K miles in 17 years, your car has done a lot of sitting. What is the climate like in the place(s) where the car has sat? Rust and corrosion can do bad things to power and ground connections.

Jeremy

I have monitored the voltage. It appears that the voltage drop is the problem and not the result of a problem with any one device.

I haven't checked all of the grounds, but quite a few. All that I checked are clean.
It has me stumped.
When it happens, it is always 7 volts on the affected circuits and 12+ on the rest of the circuits.
I would think that if it was a faulty ground, or a faulty ignition switch, that the voltage would not always be 7 volts, but would vary from incident to incident.
If it was a drop in voltage due to a large current draw then the voltage would drop on all circuits in the car and fuses should start to blow.

I will map the circuits in the fuse box that are affected and report.

The 7 Volts will probably turn out to be the clue that none of us were smart enough to pick up on.

Can you post a wiring diagram or a link to a wiring diagram of the affected circuits?

Are you using a digital volt meter? Unless you use a stray voltage eliminator, a digital meter will produce false readings in this environment making diagnosis difficult. Using an incandescent test light will produce better results as it loads the circuit.

A digital meter can help when used like this. With the meter on DC volts ( to read up to 15 ) connect one lead to the lighter socket ground ( the outer ring ) and the other lead to a good body ground. ( a bolt that leads directly to the body ) When things are turned on, the meter should read sub 0.5 V . Connect a analog meter or incandescent bulb to the positive of the lighter ( center ) and body ground.

If the car is losing connection from the ground side of the lighter to body, the meter will read 12V or so. If the positive is losing connection, the lamp will go dim / out.

The failure point is going to come down to a common power feed / ground point. We need a power distribution / ground wiring diagram to go any further.

Excellent technique!

I will give that a try this weekend.