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Discussion Starter #1
Hi, i'm almost too embarrased to ask this question, here goes...
To cut a long story short i removed and replaced the battery of my 1998 slk 230 and put it back the wrong way round (i wondered why it was a struggle to get the cables to stretch to the battery terminals- it was dark and raining, that's my excuse!:confused::confused:)
it was only for a fraction of a second and after a short crackle of electrivcity i realised. I've replaced a couple of fuses that had blown and now the coolant warning light is on permanently.
Any idea of where to look to solve the problem.

Thanks in advance, silly steve
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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disconnect the battery for 30 minutes to let all systems 'die' down, reconnect and see what happens
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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minimum 30 mins
 

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left it 2 hours started engine and light still on. Any other ideas?
Sounds like the sensor for that light got zapped. I wouldn't have the first clue as to how to prove that. I would do some research for you but I'm at work and the day is almost over, so I have no time.:td:
 

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But it runs okay? I would take it to the dealership, just tell them what happened and ask them if it's a matter of just clearing the codes? You cannot be the first one that has done that!!
 

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Discussion Starter #11
coolant level checked and on max.
good point, sometimes simplest of solutions are the answer.
 

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coolant level checked and on max.
good point, sometimes simplest of solutions are the answer.
The problem here is that on these R170's Coolant and Washer sensors share the same circuit. Meaning if one goes out the coolant level will stay permanently on. I have this issue right now. Mine always stays on. I have already ordered both coolant and washer sensors since I don't know which one is causing the problem. While coolant one is relatively easy to replace, the washer one requires jacking up the car, removing passenger wheel, and plastic covering and going from there. I will post if this cured my light as soon as I change them both!
 

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A little update on the matter, folks:

I have replaced both of my sensors but that didn't cure the problem. Coolant light was still on. So I said, oh well, I need to look at some other place but then I didn't have time and since coolant level was OK I was simply driving it. I was driving and then one day this light just stopped showing up for couple hours or so and then re-appeared again... Weird, right?! o_O

Then today, I noticed that my engine temp is a little higher than normal considering it was around 60's today and very windy. So I came back home, popped the hood and saw... that I didn't have any coolant in the expansion tank... I was like oh no... must be a leak somewhere. Thus, I started investigating and found that top of the fan was in this white-ish residue from the coolant (since coolant is 50/50 with water, water evaporates and coolant dries into white powder). So I look at the coolant reservoir tank and see that there is a small drip accumulating. So I thought the hose just came loose and tightened it up but no... drip drip again...
So I drained coolant, took this reservoir off and found out that it got a small crack right in the place where a small, few inch hose connects on top of the engine. Plastic went bad over the time I guess. Besides this part was replaced with another part... Wonder Why??? :biglaugh:
For now I fixed it with plastic JB Weld. Don't know how it will hold but it's not catastrophic and I can live with it till my new tank arrives. $53 from online dealer, $60 shipped total.
Another interesting thing that I found is that when I took coolant reservoir off I started giving it a good wash with my garden hose and suddenly the round magnet fell out... I was like ah you little bastard, that's how you look like... but wait, why did it fell out? Turns out this magnet has to sit on the float itself. There's a post on top of which float sits and moves up/down depending on the coolant level. About a year or two ago when I was cleaning this tank I noticed a rubber grommet on the bottom of the tank. It was badly deteriorated to the point that it simply washed away with the garden hose water pressure... I think that was the grommet that used to keep this magnet in place...
Long story short, I think that's the source of my problem... where magnet is not sitting in place, hence the contacts on the sensor are always closed resulting into low coolant warning.

My stupid self didn't realize that I could have taken a stronger magnet and apply it to the sensor to see if low-level light disappears... :biglaugh:

When new tank arrives I'll post a DIY on how to change it =)

Sorry for long writing but hopefully one day someone will find it useful!

Oh, here's a good explanation of how coolant level light works on our SLK R170:
Coolant Level Sensor: Description and Operation
Clicky Clicky! as Woolly says :Beer:
 

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Thanks for the information in this thread. I had the intermittant coolent light on on my SLK200, and had mistranslated the Germany manual and thought the light was for low oil level (which was obviously not low). I was going to keep checking the oil and ignore the light. After checking the overflow tank, I put a couple ounces of anitfreeze in and no more light.
 

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Another update:

The culprit was 100% found and identified!
After patching tiny crack with JB plastic weld I put coolant tank back in place and filled missing coolant back in. Drove car yesterday and no leaks so far. That should be enough for couple days until my new coolant tank arrives. :tu:
The coolant light no longer comes on, since magnet is somewhere in the tank and is sitting on top and contacting with the sensor, telling him - hey, it's full ;)
The suspect, identified as "small round magnet", has proven guilty :biglaugh:
Who knew that this tiny magnet could cause so much trouble???
Well, at least I have installed two new sensors and can rest assured they won't go out any time soon :biglaugh::biglaugh::biglaugh: I also found out why washed tank leaks out when coming to a full mark. My filling neck was loose. After I snapped it back in place, I don't see a puddle of water under my car after re-filling washer tank.

At least I learned couple things:
Coolant and washer sensors share the same circuit.
Detecting a bad sensor:
Measure voltage at the coolant sensor by taking sensor off. It should show (as far as my memory goes) 4.6 volts.
Reconnect sensor, apply magnet to top of the sensor an see if light disappears. You can measure voltage when magnet is not applied and when it is. I'll try to test it out when I'll be putting new tank in place I'll check what voltage it should show.
Fix it asap, since you never know if there might be a crack and coolant will start leaking, hence sensor will alarm you! Fortunately for me, I kept an eye on the temperature when driving with my problem and caught the leak in right time!
 

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Dear JaysonM,

which online dealer did you get your parts from? Thanks.


A little update on the matter, folks:

I have replaced both of my sensors but that didn't cure the problem. Coolant light was still on. So I said, oh well, I need to look at some other place but then I didn't have time and since coolant level was OK I was simply driving it. I was driving and then one day this light just stopped showing up for couple hours or so and then re-appeared again... Weird, right?! o_O

Then today, I noticed that my engine temp is a little higher than normal considering it was around 60's today and very windy. So I came back home, popped the hood and saw... that I didn't have any coolant in the expansion tank... I was like oh no... must be a leak somewhere. Thus, I started investigating and found that top of the fan was in this white-ish residue from the coolant (since coolant is 50/50 with water, water evaporates and coolant dries into white powder). So I look at the coolant reservoir tank and see that there is a small drip accumulating. So I thought the hose just came loose and tightened it up but no... drip drip again...
So I drained coolant, took this reservoir off and found out that it got a small crack right in the place where a small, few inch hose connects on top of the engine. Plastic went bad over the time I guess. Besides this part was replaced with another part... Wonder Why??? :biglaugh:
For now I fixed it with plastic JB Weld. Don't know how it will hold but it's not catastrophic and I can live with it till my new tank arrives. $53 from online dealer, $60 shipped total.
Another interesting thing that I found is that when I took coolant reservoir off I started giving it a good wash with my garden hose and suddenly the round magnet fell out... I was like ah you little bastard, that's how you look like... but wait, why did it fell out? Turns out this magnet has to sit on the float itself. There's a post on top of which float sits and moves up/down depending on the coolant level. About a year or two ago when I was cleaning this tank I noticed a rubber grommet on the bottom of the tank. It was badly deteriorated to the point that it simply washed away with the garden hose water pressure... I think that was the grommet that used to keep this magnet in place...
Long story short, I think that's the source of my problem... where magnet is not sitting in place, hence the contacts on the sensor are always closed resulting into low coolant warning.

My stupid self didn't realize that I could have taken a stronger magnet and apply it to the sensor to see if low-level light disappears... :biglaugh:

When new tank arrives I'll post a DIY on how to change it =)

Sorry for long writing but hopefully one day someone will find it useful!

Oh, here's a good explanation of how coolant level light works on our SLK R170:
Coolant Level Sensor: Description and Operation
Clicky Clicky! as Woolly says :Beer:
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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zouk,

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