m104 3.0 Drain battery. Problem with OVP relay
 

Hi

I need some of advice because i have quite a big problem with my w124 3.0 with KE-Jetronic and i don't have any idea how to resolve it :(.

Battery after one night is completly dead. I measured power consumption by connecting in series multimeter. Consumption was about 0.01 amps so i was quite suprised because thats good result. After a while I found something strange. When I started the engine, then I stoped it and turn off ignition I still have power on whole kejetronic... Idle speed valve, air flow potentiometer and also diagnostic socket (between pins 3 and 5 there is 12,5V). So I looked at OVP relay, and Voila. When i took off fuses from that relay, coils and ABS pump made "click" and power was gone :) I looked into diagram on OVP relay. Pin number 30 this is constant plus, 31 a ground and at the pin 15 power is only when the key is on. So I thought that something is wrong with ignition and pin 15 still have power even when key is on. But unfortunately no :( Even if I pull of the key and close the car, pin 15 does not have power. I don't understand how it is possible that coils are still egaged even if pin 15 does not have +12V. I changed OVP for new one but still the same.

Could you give me some advise? :-)

Thanks a lot.

s:

Consider the possibility of a shorted diode in the alternator, either in the main charging rectifier, or in the secondary, energizing circuit.

Battery is charging correctly (13.8V) so I may think that alternator is in good shape, but tomorrow I am going to check diodes.

Whats that mean ? :o



There is one thing which I forget about. I don't know whether this may be connected with main problem, but ASD doesn't work at all. ASD light is flashing all the time and orange triangular on dash only flash one times when I turn key on. I wanted to check blinking faults in 16 pin diagnostic socket but pin 5 is shorted to the ground... So when i connect "flashing device" into this pin, LED flash all time. I thought that ASD unit is broken/shorted or something but when I pull of it, main problem didn't resolve.

Is you car electrics the same as the W124? You have this charging light in the dash, if the bulb is not alight after you turn your ingnition on, then the bullb is shot and its the inciter for the alternator citcuit So no light, no charge to battery . Regulator can give a number of problems .See Kent Bragsna on youtube..

13.8V is a bit low; 14.2-14.5V when a good battery is at full charge.

There are six diodes in the main rectifier, and another three diodes in the initial energizing circuit for the field.

13.8 is perfectly normal. Regulators for this era were typically limited to 14V. That number could go lower depending on temperature, load, and state of battery charge.

I don't think this is a shorted diode. Maybe an ignition switch problem.

I also thing that 13,8V is not bad result.


I don't think so because I if not run the engine, only turn key to ignition and then turn off it, coils in relay are open and then close properly. There is something wrong just when the engine is running (so problem with alternator is quite logical). I just can not understand how it is possible that coils in OVP are shorted when on pin 15 there isn't any voltage :confused:



I made another simple test. I disconnected both cables of alternator, then I starded the engine. Problem didn't resolve so I am almost sure that alternator is not a reason in this case :(

Sorry for double post but few minutes ago I replaced voltage regulator and unfortunetly it didn't resolve the problem. :(

Bulb of battery is on when I turn the ignition on and after I start the engine it goes off so I think there is everything okey with alternator and battery (yes, I replaced it too)

The antenna's on cars from this era are notorious for draining the battery. Pull the fuse for that circuit and see if it helps or if you like - measure current across it with fuse out.

Do a search on this. Numerous discussions.

Have you read my first post? :)

There is only problem with OVP relay and fuses inside it.

I firstly checked all fuses in fuse box of course but there is everything alright :( Unfortunetly... :)

SZAMIK Can you google this Mercedes Benz Model 124-m104 Maintenance Manual Its all in there how to check it ,but searching is time taking. let me if its of any use to you .

I've been having a battery darin on my '95 E320 and found this thread so I am re-awakening it again in case someone runs into this again.
The first thing I suspected was a bad diode in the alternator so I yanked the battery to have access to the terminal where the cable to the alternator is attached. replaced battery temporariy and using a dc ammeter I measure the leakage again and it was still arond 1.5A on a 10 A analog meter.
pulled fuses one at a time and only the fuse for the radio etc made a tiny deflection under 0.1A not anything to consider a significant amount of current.
I disonnected the antenna motor in the back, nada
I lthought of the relays behind the battery and pulled the cover.
Out of curiosity I disconnected the ABS module Voila! thats it!
Now waiting for a used ABS module to see if swapping it will remedy the problem, if not that then I suppose it could only be the ABS valve assy. I dread havng to replace that!
It was sugested that another possibility is the key switch is not disconnecting the ABS circuit. If I had a good wiring diagram I could check that out. Wil have the module in soon and report more on this later.
DDH
PS
Meanwhile I'm running w/o the ABS working, the module disconnected. Anyone done that before?

Electrically speaking, a battery will discharge faster over a load with least resistance. Something is draining the battery by offering a relative connect to ground, even if you shut your engine and remove the key. That said, figure out a way to measure current at various places while everything is off. Watch for wires touching each other or the body/chassis.
Now, if the draining is happening while the car is on, then your charging system isn't keeping up. Sometimes some relays can also cause a diversion of power to protect other components. Sometimes a module such as the ABS could eat up more energy thus offsetting compensation from the charging system.

had the same problem with my 1990 420 sel, drove me crazy , then a lil bird told me to disconnect the antenna plug in the trunk, charged the battery never had a problem after that, even though antenna worked fine at the time, I dissected the antenna motor box found it rusty and corroded inside.