LOW COOLANT lamp on permenently. - Page 2 - PeachParts Mercedes-Benz Forum

dkveuro · #16 01-19-2004, 10:44 PM

Second update :
Let me try to explain what I have just found.

I took a chance and back probed the stalled fan wire with a 12 volt test lamp. There was a brief (three I think.) flash and then a wait of 20 seconds or so and then another brief few flashes...

On the 'running' fan there is a constant impulse flashing controlling the speed of the fan. In fact, when I put the #2 fuse back earlier, the fan ran faster than it is now.

Seems the module/ecu/ whatever, is checking the fan or is faulty, sending only brief 'run' pulses. Seems it runs something like the blower control module does in 126 cars.

So is the fan bad or can/should I fire it up with portable 12 volts ?
dk

dkveuro · #17 01-19-2004, 11:04 PM

Wow, this puppy is getting a life of it's own !
Tested the passenger side fan with 12 volt supply.
At first it wouldn't turn, then I hit it in the center and it began to spin up, the longer I held 12 vdc the faster it got but with a 'cheep' noise every rotation. Let it stop and would not run again unless it was bumped ..ran engine to warm and kept spinning/bumping the fan but it would not run up...seems like we got us a dead fan.
Going to remove and investigate....keep you posted.... s'not like anyones interested or anything !

dk.

Gilly · #18 01-20-2004, 06:09 AM

I'd follow that diagnosis, sounds like you're on track. I agree about the blinking, it's trying to get it running. I'm sure the weather isn't that hot in OK right now, but in a few months if the owner gets stuck in heavy traffic on a hot day, that monster is gonna need both of those fans running, so it's a good investment to say the least, and possibly this will cure the low coolant lamp.

Gilly

PS you could try disconnecting the "good" fan and see if that one blinks also if it's unplugged, interesting to test it that way.

KenP · #19 01-20-2004, 11:43 AM

dkveuro-
Have looked at the detailed electrical schematics for the 1996 W140 Coolant Level indicator and don't see any relationship to any other sensors or circuits except for the power side. (it shares a power buss).
Its a simple circuit (at least according to the documentation)... the indicator bulb has +12 to it whenever the ignition is on... the other side of the bulb completes a circuit to ground through the level detector in the overflow tank.
There's a "sliding" ring that floats over the sensor in the tank... is it possible that when the car lost its coolant previously, this ring has become stuck in the low position? I hate to ask, but have you checked the continuity of the sensor? According to the schematic, when the tank has coolant in it, the sensor should show "open".
If you want me to send you the schematic, send me an email with your return address. Its too big to post here.

dkveuro · #20 01-20-2004, 03:29 PM

New sensor.

Pulled sensor out of housing slowly trying to duplicate float ring influence on sensor, but light still on.

Disconnected sensor: Lamp on.

Disconnected Washer sensor: Lamp on.

Disconnect any combination, washer/coolant : Lamp on.

Lamp now covered with small square of electrical tape !

Fixed bad fan by removing and freeing off stuck brush in holder.

Both fans now run when a/c system needs condensor cooling.

LAMP STILL ON.

Next ?

BTW this is a 6 cylinder motor....wos all this about a 12 holer ?

KenP · #21 01-20-2004, 03:56 PM

Here's a link for the instrument panel schematic that you need... without it, I think you're just stabbing in the dark.

http://www.autolib.diakom.ru:8001/CAR/Mercedes-Benz/1996/S320/SYSTEM%20WIRING%20DIAGRAMS/5932.pdf

According to the schematic, the only way the light can be on when the sensor in the tank is unplugged is if there is a short to ground between the instrument cluster and the sensor.
Wire A3 in the schematic. BRN/YEL
Hope this helps.

Gilly · #22 01-20-2004, 09:27 PM

Unplug the coolant level sensor and connect the 2 sockets together and see if the light goes off.
Sorry about the screw up on the engine in this car, don't know why I thought it was a 600.
Gilly

dkveuro · #23 01-20-2004, 10:33 PM

According to schematic the senders are on/off switches. No resistors/thermistors, etc. I imagine the the coolant switch is operated by a floating magnet inside the reserve tank being as the sender/sensor is a dry fitting with no coolant contact or saturation. I am going to run a small magnet by the coolant switch and see what happens and then disconnect the ground to each switch and see if lamp remains lit.......

dkveuro · #24 01-21-2004, 02:13 AM

Screw up, double post edit. Please ignor.

dkveuro · #25 01-21-2004, 02:39 AM

I'm getting a serious case of 'burn the damm thing to the ground' right about now. This is the deal so far.

Last night I got the fans running, the right fan had a brush hung up in it's holder.
Fans now cycle according to a/c demand.

Next, download PDF file of sensor wiring diagram.
Notice an anomally...the Brown/Yellow on the car goes to the WASHER sensor and the Brown/Blue goes to the LOW COOLANT sensor. On the diagram it is in the reverse ( ???????? )

So I remove headlamp and try to move wires to diagram spec'.
However they do not really want to go that way and I had to cut the loom sleeve back for enough slack to get the plug(s) to reach the new positions.

Switch on, lamp on. Fire her up, lamp still on !

Short across plugs ( both ) still on. Short across one after the other, still on.

Ground out the Brown wire, still on.

No shorts or sensors in at all, still on.

Checked with test lamp by shorting sensor Brown/Blue to ground,
LAMP GOES OUT AFTER 20 SECONDS !
Turn off motor, put all back as factory, lamp on !

Go back to test lamp in Brown/Blue, lamp still on, not off as before.

Put sensor on bench, use magnet by the sensor probe, DOM reads 'open' and 'closed' as I move the magnet up and down the probe.
Return all to factory, lamp on.

Run ground from Coolant sensor Brown wire, lamp on.
I lost my last post update just now.......

I checked ohms across Washer : 0.00 ohms and 173.8 ohms.
The Coolant sensor with magnet = 005.1 ohms
" " " without = ........ OL. ........ (open.)

I'm begining to wonder ....have MB sent me the wrong sensors ?
If the post by Mike is correct, there should be series resistence.

Washer sensor # A 210-540-00-45.
Coolant sensor # A 129-545-02-24.

This is burning me up !
Is the PDF file correct ? I noticed the 'ru' in the address, this is for Russian dot coms/orgs/gov etc....The file seems to be from MOD though.

Zaftra commrads, spaseeba za fsyo.

myarmar · #26 01-21-2004, 04:12 PM

Quote:

Originally posted by dkveuro

If the post by Mike is correct, there should be series resistence.

Washer sensor # A 210-540-00-45.
Coolant sensor # A 129-545-02-24.

No, that was for 97 model. 1996 has separate circuits for washer and coolant sensors.
The part number for the washer sensor should be 140 540 00 17. The one you got is for 97 car. But I don't know how it could affect coolant light.
Maybe the car had IC replaced with the wrong one for my 97? Check the p/n on it.
Mike

KenP · #27 01-21-2004, 09:05 PM

dkveuro-
On your question whether or not the schematic is correct...
I went and checked the MB schematic for my 1996 S500 in my ALLDATA account... its drawn differently, but the coolant circuit is identical electrically to that depicted in the Mitchell's schematic on the .ru site.
Simple circuit for the coolant level sensor... ALLDATA account shows a drawing of the floating ring/sensor in the tank... it operates as you think. Simple switch; on/off.
No connection between coolant level circuit and anything else.
Something obviously doesn't square with what you're finding...

Hope this helps.

dkveuro · #28 01-22-2004, 02:50 AM

Thank all, you have all been helpful and have kept me going through this nightmare.

Let me explain what the physical wiring is and how it is routed.

The CL sensor has a Brown and a Brown/Blue.
The WL sensor has a Brown and a Brown/Yellow .
The Brown wire from the WL sensor runs to ground THROUGH the CL sensor.
The Ground or Brown wire runs from the CL sensor into the loom at the right fender and disappears into the main loom traveling to the fire wall.
It is not Grounded on the inner fender as I first thought.

although schematic shows each sensor with it's own dedicated ground.

BUT, the wiring on the www.autolib,( MOD, PDF ) is showing a Brown/Yellow to the CL sensor ( ? ) It also shows each bulb seperately wired to it's own sensor, NOT SO ! Car has SHARED single Brown to ground from the CL sensor.( or at least into loom.)
I also cannot get the LOW WASHER fluid lamp to come on..
..Was so busy trying to get the Coolant lamp to go out, I did not check to see if Washer sensor would make lamp come on. I have now and lamp does not come on with Washer sensor out of bottle. The lamp comes on only with the koeo bulb check.

So what the blazes has gone wrong here. Owner stated the coolant lamp came on and stayed on after last overheat...Overheat was not catastrofic, he shut down after he noticed the smell and steam from the broken heater manifold fitting on the fire wall.
dk.

KenP · #29 01-22-2004, 08:55 PM

Just on a hunch, I went back and looked at the ECL (engine coolant level) schematic for the 1997 S320... guess what? The ECL circuit is entirely different and is tied directly to the washer tank level circuit... its here:

http://www.autolib.diakom.ru:8001/CAR/Mercedes-Benz/1997/S320/SYSTEM%20WIRING%20DIAGRAMS/6321.pdf

Also looks like its tied into the outside temp sensor.
Is it possible that although the car has a build date of 1996, it was an early "changeover" to the '97 electrical system under the hood?

dkveuro · #30 01-22-2004, 11:34 PM

..............................FIXED !................................................
You where right on the money Ken ( Quoted below.) and yes, the Schematic is exactly what I have here.

I went to MB OKC this afternoon saw my parts guy Danny. He said that the Star program lists the car as a 1997. 'V' in the VIN. However, the parts lookup shows the ECL sensor as A 129-545-02-24. which is what he supplied. (White tip.)

I told him that origonal sensor had black tip. He looked up the '97 listing for ECL and it came up, A-210-545-00-24. He got it from shelf and it was the black one. Back at shop I fitted Washer sensor back in bottle and plugged in ECL. Turned on and fired up motor.

ECL went out straight away. Guess what ? Washer lamp stayed on ! Grrrrrrrrrrrrrr, wait a minute, it just went out !!
The Washer sensor chamber needed time to fill up before turning out the lamp.............

I am NOT going to pull the ECL out to test the voltage resistence on it, it works, leave the damn thing be ! Obviously the system needs to read resistence adjusted voltage to determine which lamp to turn on. Schematic shows a logic module controlling bulb function.

FYI, if you turn the key to 'run' and the lamp(S) come on EXACTLY the same time as the BATTERY lamp does, there's a problem in the system. This system sets the warning lamps on about 1/10th second AFTER the red BATTERY lamp comes on.....

Anyway, the schematic Ken sent is correct for this wiring loom,
so it seems MB switched from a 1996 platform and installed a 1997 wire loom, because the color codes are all correct on this diagram. Also, the diag' shows internal resistors just like one of you already said. anyway, all I need to do now is install the trunk emblem and I'm finished... Whoppeeeeeeeeeee!
Thank you everyone........Don

_______________________________________________
QUOTE........
"Also looks like its tied into the outside temp sensor.
Is it possible that although the car has a build date of 1996, it was an early "changeover" to the '97 electrical system under the hood?__________________
KenP

1996 S500 W140 Coupe".................UNQUOTE

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