temp guage and rpm guage inoperative after wiring harness replacement
 

Hi -- Just installed new wiring harness while fixing leaking fuel lines, etc.

RPM gauge worked for 2-3 minutes and cut out. Temp gauge not working at all. Both were working fine before work but I was having other intermittent electrical issues over last year.

Should I check the OVP relay and replace if necessary. Should I check temp sensor/sender?

Any other suggestions?

Where is the sensor that sends to the gauge on the 1995 OM606?

Thanks!

Does the a/c compressor work? If so, the OVP relay is good. The Klima relay requires a signal from the tach before it will allow the compressor to engage. The tach and coolant temp gauge really aren't related; hard to see a single problem causing both. Check all the fuses -- don't just look, remove them and make sure each is not cracked or corroded. Remember the fuse in the OVP relay. Check the connection at the temperature sender, make sure the connector got plugged back onto the sender when the wiring harness work was done. Ditto the RPM sensor at the flywheel (below/near the starter motor).

Jeremy

Hi Jeremy -- Thanks. Will check these out tomorrow. I also removed the combination heater control valve/ aux pump to rebuild as I have a small leak there. Unplugging the sensors to the heater valve and aux pump should not have killed the rpm or temp sensor.

The coolant hoses were capped during the project. I did not touch the rpm sensor but did move the cable while doing the wiring harness.

-- Chris

Leak
 

Let me know how the leak repair goes. I've replaced that pump/monovalve assembly twice this year due to leaks. The new ones last about a month and then crack and start to leak for no reason I can determine. I'm currently working with MBNA to figure out what's going wrong.

Note that in our specific model ('95 E300) the monovalve switches coolant flow from the head back to the thermostat housing. The coolant flows through the heater or bypasses it, depending on what the Climate Control Unit (CCU) tells the monovalve. With the hoses capped there is no flow from the back of the head. I hope that won't hurt the engine. I believe the 300D-2.5 Turbo engine also uses that pump/valve (001-830-40-84).

The pictures show the second replacement (replaced on warranty by MBNA)

Jeremy

http://i323.photobucket.com/albums/n...ps6143cc3a.jpg

http://i323.photobucket.com/albums/n...psa68658df.jpg
http://i323.photobucket.com/albums/n...psbbc3865d.jpg

I replaced my assembly with another one from Germany that was used. It cracked later as well. I am now trying to rebuild but in the mean time have capped the coolant hoses. Should I loop the circuit?

Loop
 

If you've been driving the car and the engine hasn't blown up you're probably OK to continue as-is. To be absolutely sure, connect the hose that runs behind the engine to the hose that goes into the thermostat housing. Leave the two heater hoses capped.

You may have to pull the battery and battery pan to see which of the three hoses runs behind the engine. Two of the hoses go into the firewall and lead to the heater core (the same heater core is used in cars that have dual controls, hence two outlets). The third hose connects to a pipe that runs behind the engine and connects to the head.

On the forward end of the valve/pump are two hoses. The little one can be left capped -- it feeds the windshield washer bottle heater. The larger hose is the return-to-thermostat hose. Connect it to the one that runs behind the engine. That will allow coolant to flow from the head back to the thermostat and on to the radiator. May not be necessary but who knows.

If you figure out a repair please share. MBUSA has asked me to have my dealer contact an MB rep to come see the leak with the part still in my car. Maybe there was a defect in the manufacturing process.

Jeremy

Checked compressor and it indeed does not cycle on. So I have no rpm, no temp gauge and no tachometer. I have ordered a new OVP and will see if that helps.

RE: combo mono valve/pump assembly, I will interested to hear what the zone rep. has to say about it. I have thought the design was poor....the added hose connection below the mono valve looks like it is made of a different material then the rest of the assembly. The two I have have also cracked in that upper area. It may be weak material combined with the stress of the hose pulling it down.

-- Chris

FYI. The dash engine temp gauge connects to a temp sender on the engine. However I am not sure of the location on the OM606. (On the OM603, it's buried behind the injection pump). Since your model has afterglow, it may be one pin of the dual-function, 2-pin sender used for both the dash gauge as well as the afterglow relay.

If there is no RPM signal, the AC compressor will not engage. While this could be related to the OVP, it's highly suspicious that it died right after replacing the harness. Double check the connections, and the flywheel/crank sensor itself is also suspect.

The two issues should not be related.

Question: Did you install a brand new harness, or a good used harness?

:detective:

Hmmm. That makes me wonder if the two pins for the sender got reversed. If so, that would explain both the long glow time, and the dead temp gauge (assuming it remains down at 40C all the time).

:stuart:

Good news
 

The local dealer (Santa Rosa Mercedes-Benz) has agreed to replace the pump/valve as a warranty item, even though they neither sold me the part nor did the installation. They'll also send a report to Germany. It looks like the thing was made by Bosch, at least the electrical part of the monovalve has their name on it. They may have subcontracted the plastic parts and I agree they look like slightly different kinds of plastic. There may be a whole mess of these defective versions in the pipeline. It would be nice to hear from other owners of models 124.128 and 124.131, which are the only models to use that part number (001 830 40 84).

Jeremy

Any trick to replacing the OVP in this model? Should I disconnect the battery?

OVP
 

It's much easier to access the stuff in that area if you remove the battery, which obviously means disconnecting it. If you leave the battery in place, just make sure the key is off and in your pocket. The OVP just unplugs; it will be tight and I've had problems with the socket coming out of its bracket, relay and all. That's why it's easier with the battery removed.

Jeremy

Problem solved!
 

Thanks for the help! The new OVP solved the problem with the rpm gauge/compressor. I had the temp. gauge sensor reversed with the one that plugs into the back of the fuel pump.

The vehicle runs a lot better.

My next project will be to change the belt tensioning system to quiet things down while the vehicle is idling.