Gremlins emerging - PeachParts Mercedes-Benz Forum

95E320cab · #1 10-11-2006, 02:19 PM

My car has a little creature playing tricks on me:

The reverse lights only work on occasion.
Also, the seatbelt extenders work only on occasion.

It's peculiar to me that the two are apparently on the same circuit, because one's intermittent operation coincides with the other. They don't appear to share a common fuse.

Any ideas how to begin tracking down the apparent short circuit?

Thanks all

Gilly · #2 10-11-2006, 06:45 PM

Do you know the reverse lights aren't working occasionally because you get the lamp failure warning on the dash, or some other way?
When the seat belt presenters are inop is it both sides, and also is the dome light going off when these fail, or is the dome light turning off?
Gilly

lee polowczuk · #3 10-12-2006, 09:20 AM

as soon as you figure out the seat belt presenter thing, bottle the knowledge and sell it.

our 300ce has the same issues... some times both work...sometimes neither, often one or the other... these days they are not working more than working..

i will have to check the reverse light thing and report back....

95E320cab · #4 10-12-2006, 11:07 AM

Hello Gilly:

The presenter only malfunctions on the drivers side. I know that the reverse lights don't work because I can back up to a window or another car and see the reflection; the indicator on the dash does not indicate a bulb failure.

When the presenter works, the reverse lights work. When the presenter does not work, the reverse lights don't either.

The dome light always works when the door is opened, so I know its not that switch.

Thanks for your interest.

Lee, if we work it out, no charge for the knowledge.

95E320cab · #5 10-16-2006, 02:11 PM

Hello friends. Just thought I'd pull this one back up to the front page. Still no resolution. Any ideas? Thanks!

Gilly · #6 10-16-2006, 04:17 PM

For the reverse lights I'd try replacing Fuse 7. If it's not that it could be the neutral safety switch.
For the presenter I'd look closely especially at fuses C, 3, 5, and 9. Either of these could also be caused by a bad connection under the fuse board itself. I'd be more inclined to think of a bad motor assembly, possibly one of the limit switches is bad, but I don't believe they are available as a seperate part. To be absolutely sure you'd need to remove the motor assemly and test for voltages at the proper wires, preferably in the failed state.
Gilly
PS, One thing you wouldn't normally notice: when this problem is occurring, check to see if the outside mirrors are also not working......

95E320cab · #7 10-17-2006, 05:24 PM

Thanks Gilly. I'll double-check those fuses. I checked at lunch today regarding the outside mirrors - the motor to move the mirrors worked even thought the reverse lights and the seatbelt presenter did not.

There must be some common wiring for these two functions, and there must be a short or bad connection in that common wiring. I just don't know exactly where to start checking. I have had the back seats and side panels out. I could get back in there and see what I can start to eliminate. Thanks for your suggestions. I'll post any progress as I make it.

Getting busy at work for the next three weeks or so. It may have to wait.

Gilly · #8 10-17-2006, 06:31 PM

I looked pretty hard at the things in common between the presenter and the reverse lights. Came up empty handed. Maybe I should check through again. Might just do that to be sure. It might make it easier to go through just one of the systems, I'd think the reverse lights would be easiest. Then we'll see if one fixes the others. The presenters do go bad, especially the drivers sider as that one works more often. The only other thing I'd like to know is about the seat belt warning buzzer, does that act as it should? That would be more related to the presenter than the reverse lights. I'll see if I can post something about exactly how the reverse lights operate. Do you have a volt meter and cofident enough to use it to test the circuits if I put this info up?
Gilly

95E320cab · #9 10-18-2006, 01:17 PM

That's great Gilly. Thank you. I do have a volt meter and can use it with some degree of confidence.

The seatbelt buzzer always works. Sure is annoying.

I have not mentioned in previous posts, but I frequently get a little shock when I'm getting out of the car and closing the door. I've attributed it to a static charge, with all the dry heat we've had in Texas this summer. It's been a while since I was schocked, but I learned where to touch to avoid the shock. I wonder...???

Gilly · #10 10-18-2006, 04:30 PM

Nahhhh

Gilly · #11 10-18-2006, 04:55 PM

OK your note made me remember to look at the schematic

thanks.
Here is the way the reverse lights work: Starts at fuse 7, from the fuse box it goes to S16/1, the starter lockout/backup lamp switch. Power goes in at the #1 terminal (that's a black with red tracer wire) and out on either socket 2 or socket 7, couldn't make sense on why "7" was in parenthesis, either way it would be a gray wire with yellow tracer. From there it goes to N7, which I believe is in the rear of the fuse bx, it's the exterior lamp failure monitor module. This wire connects at connector 1, socket 13. Each reverse light has it's own circuit leaving N7, they are on connector 3, socket 5 and 7. They then just go back to the rear lamp units. Each side has a different ground, so it's not a ground issue (or really unlikely that it is anyways, since they both fail at the same time. I'd concentrate more on the front half of it. You'll almost want to test in a failed state. If you can get it to fail when you want it to, like in the driveway or something, first I'd test for power at that fuse 7 first. After that you need to be under the car and test power at that red/black wire at socket 1, then find out if your gray/yellow wire is at #2 or #7, then test for continuity from 1 and 2 (or 7 as the case may be), then probably easiest to test continuity on the gray/yellow wire from the reverse switch up to that connector on N7 (connector 1, socket 13). Any questions let me know. I'll also go and look through the seat belt presenter diagram.
Gilly

Gilly · #12 10-18-2006, 05:16 PM

OK, I see one thing. There is a ground, W12 is the designator, it's under the center console. It's multi-wired of course. It provides the ground for both of the switches for the seatbelt extender, and for the motor units for the extenders. It seems to have less implications for the reverse lights though. You haven't had any work done in the center console lately, or maybe a aftermarket radio, anything along those lines, or pretty much an untouched car?
I'm not to keen on the fuse I mentioned before being the culprit, but that's the place to start, may end up being a corroded connector on the reverse light switch, but not one that would cause a starting problem. If the circuit is OK up to N7 then thinking it could be N7 itself.
Gilly

95E320cab · #13 10-18-2006, 06:59 PM

Thanks a million Gilly. That will keep me busy for a Saturday.

I think I'll try to knock around the center console. The aftermarket head unit was a tight fit. May have worn through some insulation?

Gilly · #14 10-18-2006, 09:12 PM

W12 would be in that area too, under the radio and just to the rear and right of the airbag control unit. But I think the airbag control unit would protect it from getting rubbed. How about someone tapping into a ground wire that just happens to affect the presenter? On the reverse lights I think I'd still plan on checking the wires I mentioned. Try doing it in a failed state though.
Gilly