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Coolant visit workshop help. Tried everything problem comes back.

5K views 26 replies 11 participants last post by  walt.calkins 
#1 · (Edited)
Hi all,

I am having a REALLY annoying problem that is making me start hating my car.

So I have a 2005 SLK350 (R171) with 118k miles and a few months ago it started throwing the "Coolant visit workshop" message on the dashboard.
My mechanic scanned it and said that he could not pinpoint it to the thermostat but that I should have replaced it along with the water pump that was underperforming.
I replaced both and changed the engine coolant as well.

It all worked well for a month, the thermostat was URO brand. After one month, the same message on the dashboard popped up. I thought it could be the thermostat and I replaced it with Borg Warner. Again it all worked normally until a few weeks later I pushed the engine a bit harder for 1min, just taking off at first, second, and third gear. Right after, that same message popped up and it has been like that.

The fan seems to be working and kicking in around 96 degrees, the coolant level is above the plastic fin, wiper's fluid is topped.
The main problem is that when the dash message pops up, and that's everything the car reaches around 90 degrees, the A/C stops blowing cold air and the message intermittently pops on the screen.

This is driving me crazy. Does this look like a thermostat going bad again? Could it be something that burns or kills the thermostat?
I touched the top hose coming from the thermostat when the car was hot and the hose was hot too. if the hose were cold I guess it could be a thermostat shut problem.

Any ideas what the cause could be?


Thank you, guys!
 
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#6 · (Edited)
low or high, since sensors windshield washer and coolant share

following from Dave2302 Jeff edit :D
*
What Jeff means is that they share the same wiring - different sensor and different warning lights. Because they share the same wiring if one goes faulty (usually the windscreen sensor) if can bring up the other warning light. Of course this doesn't happen if both are working properly

The Coolant Light is supposed to come on if you have a Cooling Fan issue or Low Coolant level, but it can come on if there is some other fault as discussed by jbanks15 such as Washer Level Sensor, Coolant Level Sensor, the shared Wiring or even an Instrument Cluster issue.

In this case as BaD_81 correctly says, if the Temperature isn't getting to circa 97 / 99 then the Fan is not programmed to cut in below that Temperature.

Fan is controlled Speed wise in percentage increments by the Fan Controller Module which selects the appropriate Speed in percentages by computing from a PWM signal sent from the Motor ECU.
The actual percentage Fan Speed PWM steps the ME sends to the Fan Controller are dependent upon exactly what temperature the ECT Sensor is sending to the ME.
For Example when the Coolant reaches the initial pre programmed 20% figure of ~ 97c if the ECU sees no reduction in ECT, or even a rise, it will step up to 40% etc etc.
****
 
#7 ·
following from Piet:
Did I write that? Uhmm...I wished I was that smart but credit due where credit is due @Dave2302....... 😁 😇

 
#8 ·
But maybe try an OEM thermostat instead of an aftermarket? Not saying it is your problem for sure but it is not your oldfashioned thermostat that opens at a certain temp and closes below a certain temp.
Thing is controlled by the ECU and depending on several variables ECU controls it with a PWM signal to open or close it a certain amount. Maybe something goes wrong there?
Read this for an overview
 

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#9 ·
Th aka you for the information.
I don’t think it could be coolant level too high. I could be wrong though.
It could be something to do with the ECU, but then why it was temporarily fixed when I replaced the Thermostat? Cause right now every single time I drive the car’s malfunction IC message pops up. Just like before when I replaced it the other thermostat.
I think I am going to test the thermostat resistance as per @Sneaky Pete documentation.
 
#10 ·
@FloridaMerc
I had the same issue and covered the fix here..

As both the washer level and coolant level use the same wire with a different resistance for each sensor, if one goes bad it can trigger an alert for the other.
It does seem that the coolant sensor goes bad most of the time but Is very easy to replace.
 
#11 ·
@FloridaMerc
I had the same issue and covered the fix here..

As both the washer level and coolant level use the same wire with a different resistance for each sensor, if one goes bad it can trigger an alert for the other.
It does seem that the coolant sensor goes bad most of the time but Is very easy to replace.
I guess I could try replacing the sensor too.
My IC does not say low coolant nor low washer fluid though. Could this still be the case?
 
#13 ·
How can I check flow in the radiator?
another interesting think is that, in order to drain the old coolant I was not able to open the radiator valve. I turned it with a screw driver but I wasn’t able to open it up. Nothing came out of it. I had to disconnect one of the low hoses instead.
 
#14 ·
Without seeing the codes it's hard to say what part it is, themostat, level switch, temp sensor, etc.
You need to scan it again, preferably with SDS, and post the exact codes here. Find a mechanic with SDS if possible - accept no substitutes. There are some "almost as good" scanners that may help in this case, but a mechanic with actual SDS is going to be your best bet.
 
#19 ·
I little update.

Replaced both coolant level and temperature sensors; drove almost 20miles then same problem again: "coolant visit workshop".

I noticed that sometimes just before the fan engages, it kinda "tries" a couple of times before fully engaging. Could it be a problem with the controller?
 
#21 ·
Code P0694 - The output of electric fan has a short circuit to ground.

I went ahead and tested the cable wires that connect to the radiator's fan, the Power (thick red), the ignition power (black striped), and the Ground all working. I don't have an oscilloscope to test the PWM wire.
I could try replacing the Relay "I" which is supposed to be for the fan.

I hope it is not the ECM. The fan does not always fail, but sometimes (sometimes the car goes longer periods of time without throwing the error sometimes less) it does by trying to engage (moves just a little bit) then it stops and throws the error.
 
#24 ·
Hi FloridaMerc

Wondering if you figured out the issue.

Also have a early 2005 R171 with 63K that is also having the display symbol that looks like yours popping up in the instrument cluster. Note in my OEM user manual the "Coolant Check Level" is a different symbol. As with you after the symbol pops up the air conditioner shuts off and just the compartment fan continues to run. Checking the coolant temperature in the instrument cluster, it is always 90 degrees and steady after the symbol pops up (note... it is also 90 degrees and steady all the time after the engine is warmed up). The message will appear in the stored message window as long as the car is running. After you turn off the car and then restart the car the stored message is gone. Before turning off the car, after the symbol has popped up, I have checked the engine fan and it is on and working.

Sometimes I will drive the car 20 miles and the symbol will not appear and sometime after 2 miles the symbol appears. Have also changed the coolant level sensor and the washer level sensor (both OEM) with no effect. Scanned the codes (using iCarsoft CR MAX) and like you I did get the ECM 0694 code (the output of electric Fan 1 has a short circuit to ground). Cleared it a few times yet if appears to come back. For the symbol, my OEM owner's manual list possible solution as the poly-V belt yet this seems weird.
 
#25 ·
Hi FloridaMerc

Wondering if you figured out the issue.

Also have a early 2005 R171 with 63K that is also having the display symbol that looks like yours popping up in the instrument cluster. Note in my OEM user manual the "Coolant Check Level" is a different symbol. As with you after the symbol pops up the air conditioner shuts off and just the compartment fan continues to run. Checking the coolant temperature in the instrument cluster, it is always 90 degrees and steady after the symbol pops up (note... it is also 90 degrees and steady all the time after the engine is warmed up). The message will appear in the stored message window as long as the car is running. After you turn off the car and then restart the car the stored message is gone. Before turning off the car, after the symbol has popped up, I have checked the engine fan and it is on and working.

Sometimes I will drive the car 20 miles and the symbol will not appear and sometime after 2 miles the symbol appears. Have also changed the coolant level sensor and the washer level sensor (both OEM) with no effect. Scanned the codes (using iCarsoft CR MAX) and like you I did get the ECM 0694 code (the output of electric Fan 1 has a short circuit to ground). Cleared it a few times yet if appears to come back. For the symbol, my OEM owner's manual list possible solution as the poly-V belt yet this seems weird.
 
#27 ·
I chased this same problem on my 05 SLK 350 for almost a year. Very annoying. The dash message was "coolant visit workshop". I changed the washer and coolant reservoir sensors, although now I dont believe they are related to this code. The code for these sensors would be "coolant level low", or "washer level low". I replaced the thermostat and coolant reservoir cap, and coolant temp sensor, no success. I finally found a very small crack in the plastic radiator tank was leaking directly on the plug for the electric cooling fan, causing intermittent operation. Replaced the Radiator and cooling fan and problem solved. Mileage at time of repair was 165000. Walt
 
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