Water in CIS-E Unit Connector--560SL - PeachParts Mercedes-Benz Forum

downeyjc · #1 11-11-2003, 01:24 PM

The Car: 1988 560SL with 106K, owned for 8 years, lightly driven.

The Owner (me): Tends to get in over his head when working with electrical problems and should invest in better diagnostic tools. Owns a second 560SL that helps improve his diagnostic capabilities and provides a source of test parts when needed.

The Problem: Car takes at least 3 tries to start when cold. Once started it runs slightly rough but evens out and then is fine. Restarts easily when warmed up.

The Repair Saga:
1. Checked the obvious things (plugs, wires, fuel supply)—all OK.
2. Found there is NO voltage at the EHA valve connector, with ignition ON. Compared results with car #2 and found it had 5 volts at connector with ignition ON.
3. Proceeded to replace OVP relay with known good relay and rechecked voltage at EHA. No change in symptoms.
4. Proceeded to check wiring from EHA connector to CIS-E Control unit. Yikes!! When I removed the 25 pin connector to the unit, water starting dripping out. All told about a teaspoon!! Pins 10,11,12,13, and the adjacent pins 22,23,24,25 all wet and covered with surface rust and corrosion. Can only assume moisture came from earlier door seal leak, where floor mats got quite wet.
5. Cleaned the male connectors on the CIS-E unit—no evidence of water seepage into the unit itself.
6. Checked harness connector and found same corrosion in the female sockets for the same pins. Disassembled the connector, cleaned the sockets and blew out all moisture with compressed air.
7. Reassembled unit and said a quick prayer. Didn’t fool anybody—still no voltage at EHA connector.
8. Validated that power is getting to CIS-E Unit—pin 1 is hot.
9. Noticed that O2 sensor light does not come on when key is in on position. It is connected to pin 15 which is adjacent to the area that was corroded. Could be bad bulb, but not likely.

The Question:
1. I initially planned to swap the control unit from Car #2 to positively confirm the “wet” unit was bad, but they appear to have different units. The suspected bad unit is a VDO 006 545 82 32. Car #2 is a 1987 model 560SL and it uses a Bosch unit 004 545 40 32. I’m not willing to risk the swap without knowing if these units are interchangeable. Anybody know for sure?
2. If the CIS-E unit is shorted out, what are the chances that it took other things with it, such as the EHA valve or O2 sensor?
3. Lastly, I’ve read a few posts that indicate these units are very durable and are dirt cheap at junk yards. Haven’t been able to find one online for less than $250. Is this the going rate? I’m not in a hurry, so I can shop around.

Thanks, John Downey

mbdoc · #2 11-11-2003, 05:48 PM

That was a problem on ALL 560SL's. MB offered modified wiring harness to keep water from the CIS-E computer. MB part number 107-540-24-34. Only info is inner-office memo on the problem, never reached SI status.

The replacement numbers for the computer are 006-545-82-32 OR 006-545-96-32, orig number was 004-545-40-32.

$250 is a GOOD price

downeyjc · #3 11-11-2003, 09:48 PM

Thanks, M.B.DOC. The interchange numbers are a BIG help in looking for a replacement. I think I may have the "new" harness--it was trussed up pretty good with a tight rubber boot--hard to believe water got in there. I plan to wrap the entire unit in plastic if I have to. jcd

mbdoc · #4 11-12-2003, 08:00 AM

Water is running DOWN thru the wiring harness. Gets in the harness under hood!!

downeyjc · #5 11-12-2003, 10:20 AM

M.B.Doc: Many thanks. That will require a different approach, but at least I know what to look for. It must be an awfully slow leak, as this car is stored inside, driven less than 3000 miles per year, and it's never in the rain. Of course, I wash it frequently, so that may be the source. I'll trace the harness and look for entry points for water. Thanks again.