LOW COOLANT lamp on permenently.
 

Hallo everyone....I have posted this to iATN tonight but thought there might be some info available from here too....well, I can only hope !
Driving Miss Daisy this ain't.... Crazy more like !

POST AS FOLLOWS about a 1998 S320W straight 6 twin cam sedan.. VIN # WDBGA32G6VA334301. Build date : 7/97

CLOSED W/SUMMARY

Well, hallo everyone ! It is 00:23 on Monday morning. Just
finished all I could do on this MBZ........You wanna know
what happened ? Okay, get a cup of coffee and a comfortable
chair and 15 minutes spare time, this is gonna be a l-o-n-g
one. You ready? Right, MBZ of OKC eventually sent me two
looms as per last problem with mirror wires shorting. These
turned out to be incorrect looms,called back and eventually
drove to Mercedes of OKC and dropped off looms hoping to
see about correct looms. Seems parts man knew I was coming
and I was told he's off for the day ! So, next day I call
and he says he's going to have to look up what was
available to fix this loom deal. A few days later he called
and said he has gotten information that says that only cure
is to install complete mirror assemblies. Okay, so how much
are they ? $616.00 each ! Pretending not to be suprised, I
ordered the drivers door mirror only, 'cose I'd run out of
money buyin' loads of parts for all these other MB's
sittin' in my shop.A week later it arrives, because, as we
all know, the reason there are holidays is so parts guys
and UPS can screw you around with delivery delays.....Nuff
said ! Anyways, this parcel arrived with a COD balance to
pay against the credit on the looms. Okay, part
#210-810-21-16 LT MIRROR. is checked for busted up whilst
in UPS custody....all okay. Now this afternoon at 14.00 hrs
I gave in to the need to see if I could install mirror
without recourse to dynamite. Here's the skinny for those
of you contemplating replacing a door mirror on a 140 with
power folding mirrors, (I guess the power fold back is good
for another 12 mph on the autobahn, heck, who the blazes is
gonna be concerned about looking in the mirrors to see
who's behind you at 145 mph anyway ? ) Anyway, I digress,
with the mirror folded half way back, close the door and
grab the mirror body and pull it forward and out to expose
the clockwork. Don't worry about the creaking and snapping
noises...If you look all the way in from the mirror side at
the joint, you will see a spring steel wire running top to
bottom held in the center by a tiny finger. With a probe,
spring this wire out from it's position behind the finger,
this allows the two ears at top and bottom to disengage the
mirror body and you can slide the plastic body off the
motorized mirror assembly. Next, you will see three
phillip's head screws holding the assembly to the
door.Remove these and swing mirror away from body with the
rubber gasket, then you'll see the two loom connectors to
the mirror, these pull apart without needing to release any
clips or hooks, and, as they say in most of those dumb
books, 'reassembly is reverse of disassembly.' My problem
was that I had to fix the loom shorting in the right door
mirror too, so I pulled the body off the assembly and cut
the wires to the mirror swivel head, leaving the folding
feature wiring in place so no short would happen, but now
there is no mirror adjustment on that side, only fold. It's
a wide angle mirror so position is not too critical....So,
didn't need two hulking great looms, only mirror head. Job
done, just need owner to authorize right mirror relacement
at another $616.00 plus. So button up the new 'WASHER'
sensor and put all the engine covers back in. Guess wot ?
New 'COOLANT' sensor too. The flaming 'LOW COOLANT' lamp is
still ON !!!! Okay, installed extra ground wire after
cleaning up the two inner fender stud grounds, but lamp
still on...I guess some black electrical tape will have to
do over the warning lamp, I see no reason apart from the
rat may have got into wire loom I can't see or acsess in
the engine bay, although I spent a lot of time looking. Any
more ideas folks ? Everything back in I had removed to get
at a rat's nest under the A/C intake plenum.....Stinky job,
used a painters face mask doing that job as don't need to
contract Bubonic Plague ! Washed it down with diluted
hydrogen peroxide. Next put the Snap-On scanner in to check
all's well. Two codes come up, Missfire #4 cylinder.!!!!!
WHAT ? Ran engine up and sure enough, miss, engine rough.
Took intake off and removed plug cover....DUH, water had
run into cover valley and trickled down into #4 plug
resess. Dry everything out and clear codes...run to warm
and recheck, missfire comes back ! Out comes stetherscope
and I listen to injectors. # 4 not clicking. I know that
the ECU will shut off an injector if missfire values get
above a set value. So, remove coil for #4 and checked for
spark, big fat spark and no fall out. Wiped with dilectric
grease and refitted to engine. Cleared missfire codes and
ran to warm again.....Oh yes, by this time it's 21:30 hrs !
Engine ran smooth. Tried to kill injectors with Snap-On
scanner in 'actuations' feature, but system would not allow
it. Tried 'OFF' '' and 'HELP' menue but still would not
kill selected injectors. On this cartridge there is no
'TROUBLESHOOTER' menu, wanna tell us why, Snap-On.

So, all codes cleared and closed up for test drive. Washed
up and headed out for the WAFFEL HOUSE. About 5 miles into
trip with 'cruise' set at 65mph the ASR lamp comes on,
cycled key off/on quickly and lamp stayed out for rest of
trip of 12 miles plus trip home of 16 miles...Strange !
Also noted the brake pedal is dropping some at stops. Back
at the shop I bleed all wheels, no air, no change, still a
lot of pedal drop at stops. ABS functions okay and stopping
the car is fine but needs a little more travel than I would
like to see. Mmmmmmmmm ? So the upshot of all this is, why
is my LOW COOLANT lamp still on ?.......Hey, you fallen
asleep out there ?.....BTW, code clearing will not always
work if you don't take the key out for a few seconds before
restart or retest, so if any of you are still with me after
all this I'd appreciate any tips you might have. Failing
that, it's a day's subscription to www.Mercedes on line web
site. Being as this is my last post for this HELP mail, you
can email me at dkveuro@juno.com if you have info' or
wiring schematics. For those of you who sent emails about
the COOLANT lamp, thank you for taking the time and trouble
to reply. They where all gratefully recieved. Thanx once
again.......Regards everyone, dk.

END OF iATN POST.

To continue.........

Hope I didn't offend anyone doing this.....need help bad on this.
Becoming the car from hell. BTW, would front to rear worn tyres cause this system to flash the ASR ? All tyres are same size though. Just that back tyres need replacing.
Thank you....dk

I'm thinking that car still uses the series circuit between the coolant and windshield washer fluid sensors. For some reason the IC (instrument cluster) figures out the wrong one.

Try disconnecting the washer reservoir sensor and see what happens. (I don't know what should happen so goog luck)

Steve, disconnecting either coolant or washer sensors has no effect on the warning lamp. It remains on.
Both sensors are new from MB . The voltage on the Brown/Blue wire is 8.46 vdc and 0.085 vdc on the Brown wire and 0.0056 ohms on the Brown wire to ground, measured at the plug connectors or at a peiced point down stream.
I think the 'black electrical tape' idea is workable !!
dk

I told customer about problem and he now tells me the heater manifold block against the fire wall broke and engine overheated. This is when the Low Coolant lamp came on. Been on ever since then he says. Any possible connection with another sensor ?
Wish I had schematics for this....dontcha just love it when they feed you a little bit of history at a time !!!!? Grrrrrrrr.
dk

That sensor won't go in upside-down, will it?
Steve, I think the set-up you're talking about that links the 2 sensors together originated with the SLK 170 chassis, I don't think the 140 works that way, individual circuits.

Gilly

The W/washer level sensor is in series with the coolant level sensor on most 1997 (1996 on the W210)& later cars. The cluster MUST see some(but not full) return voltage OR the coolant light will stay ON!
The coolant sensor is a ON/OFF circuit & the w/washer sensor is a variable resistor.

Some reason I read E320. Ooops

I have schematic for 140 as of 97.
S41 ECL switch has 170 Ohm resistor inside. S42 Windshield Washer switch has 110 Ohm resistor. The switches are in series and normaly open. So in normal condition IC would see 110+170=280Ohm.
If one of the switches gets closed resistor in this switch would be shorted out, and IC would see either 110 or 170 Ohm.
Reg. Mike

Okay guys...I've been known to get a chassis type wrong before, so let's clear up the cars id.

1998 S320W straight 6, twin cam, automatic, sedan..

VIN # WDBGA32G6VA334301..... Build date : 7/97

I hope I didn't throw a curve ball in there saying anything about a 140 .... Steve, you and me have gotta pay more attention old son !
I'm going to introduce a little more voltage into the circuit with a variable resistor pot and let you all know what happens..
Thank you for the latest info' people.
dk.

Did I say 'Pay attention !' Well I thought I'd double check the VIN and Build Date....Guess what? Build Date should read 07/96...
NOT, 97 :rolleyes:
.Crap, this is wot comes of working untill 3am on Monday morning.....SORRY folks.
Okay, I'm going to do that test voltage now....see you later...dk.

IF you really can't find a problem with the sensor chain, there is one other thing I've seen. I wouldn't have thought it would pertain to this chassis, but then again I didn't think a 140 ever used the sensor chain logic either.
I did see a 202 chassis that we absolutely couldn't figure out why the low coolant lamp kept coming on. Turns out there is some sort of relationship between either the cluster and the engine control module or the cluster and the ACC which will throw on the low coolant lamp in the event of an aux fan failure. Any chance the aux fans are inop on this thing?

Gilly

Mmmmmmmm. That's interesting. The a/c was on last nite in the shop while I was hooked up with the scanner, I never heard the fans kick in , and that was for over 45 minutes too. They get sucked into rotation at high engine speeds but never seem to run up. I think I'll check that right now....BTW, what commands FANS ?
Pressure/heat sensors in a/c lines? My scanner does not feature fans, on/off.
dk

On that model, there should be a fan control module I believe, could be wrong on that. The fans are triggered by pretty much what you are used to:
AC pressure and/or engine temps.
Use your scanner to go into ACC to see if you can run a aux fan activation routine, that's where you get to it in the MB scanners.

Gilly

Update...Car in shop.
A/C on. Set to 'LO' both sides.
Drivers side auxillary fan runs but passenger side does not.
A/C off.
Run temperature up to 205f. (Raytek, pointed at underside of thermostat housing.) with #2 fuse for FAN pulled. Intall fuse and drivers side fan runs but not passenger side fan.
All fuses eyeballed and ohms tested good.
'Low Coolant' lamp still lit.
Only one aux' fan running.

Unknown if a bad fan itself would cause the light to come on or not, or even if this problem I remember with the 202 would apply to this beast. I would rather think that an actual control problem, like a bad fan control module, would cause the light, but who knows? Maybe too little current draw from the fans would also cause it? Sadly I can't remember what the neccesary repair was on that 202 car, just that a aux fan problem = a low coolant light, some sorta MB "fuzzy logic". At any rate I would think with the big 12 holer you'd definitely be better off advising the customer to replace one of the aux fans rather than worry about the outside mirror. I mean, assuming they can actually USE that mirror to a good effect.

Gilly

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

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 !:D
dk.

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.

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.

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 ?
:confused:

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.

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

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.......

Screw up, double post edit. Please ignor.

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 ( ???????? ):confused:

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.

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

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.

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

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. :confused: 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.

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?

..............................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

__________________________________________________

Makes a pretty good case for a simple switch and a lamp, eh?

Somehow, someone decided that computer controlled everything was cheaper than wires and switchs, in spite of the fact that the wire and switch is still there, and a computer in the tail light to switch the bulb on and a high speed serial cable cost a whole lot more than a switch and a wire.....

Peter

Yep, the system as described in the 1996 schematic makes sense... the 1997 system looks overly complicated just to tell you the coolant is low... there must be a reason, but not apparent to me.
Anyway, sorry this process took so long, but lots of knowledge gained... will have to check my '96 and see how its wired... :-)
Glad information helped.