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Techspy

Low coolant light still a problem

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So I had an intermittent issue with my low coolant light coming on when I owned my S4 a few years back. I went a couple months with it not lighting up and figured it was sorted after double checking all the wires etc. Well, 5 years later and it is still an issue. I have checked all the similar issues in other threads but so far nothing has fixed the issue. Here is what I have found so far.

 

Unplugging the chargecooler and main header tanks sender wire will not cause the light to come on. Disconnecting them when the light is on will not cause it to go off (or grounding the wire either).

 

No check engine light and the engine is running fine when first started and after warmed up.

 

Freescan shows no codes and all temps are correct.

 

I have the single module in the rear relay box and when the light is on I can unplug the module and the light goes out.

 

I am really at a loss...

 

I know the Engine Coolant Temperature sensor can set this off but all temps in Freescan are fine, the engine runs fine and no codes show up in Freescan. All of which should be associated with this sensor being bad. I am guessing that I could disconnect and/or ground the Engine Coolant Temperature sensor wire the next time the light is on to see if it goes off but I recall doing that years ago without it having an effect. Otherwise, I guess the "switching relay" in the rear relay box can be bad. It looks like normal relay pin-outs but it is much bigger than a normal relay. Does anyone know if the "switching relay" as it is referred to in the service manual can be replaced with a normal relay for testing?

 

A bit more info.. Sometimes it comes on soon after starting the car even before it gets to temp. Sometimes it comes on after driving all day. Sometimes it goes right back off and sometimes it stays on for the rest of the drive.

 

Thanks for any info.

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You've not mentioned checking the sensor in the coolant header tank?

They are a very common cause of similar issues on your model of esprit as the float gets gunked up and unreliable and also the switching part also fails intermitently on occasions.

Saying that, does your S4 have the plastic header tank? If it doesn't the above is a load of bollocks!

The metal tanks have a sensor pin in a rubber bung in the side of the header tank to monitor the coolant level.

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Sorry I should have been more clear. When I mentioned the below I meant that yes it does have the dual header tanks (chargecooler and main header tanks) and that by removing the sender wire (sender/sensor wire) which doesn't have any effect on the low coolant light) that I have ruled out a bad sensor in the header tanks as the cause.

 

"Unplugging the chargecooler and main header tanks sender wire will not cause the light to come on. Disconnecting them when the light is on will not cause it to go off (or grounding the wire either)."

 

Thanks

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I have the same issue, never managed to resolve it. My light goes out only if the engine check light comes on, almost tempted to remove the bulb.

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Annoying isn't it? I am curious to know how the temp sensor activates the light. I think it goes to the ECU which then triggers the light relay. I may try to track that down and see if I can get it to turn the light off when it comes on.

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The 'Low Coolant Level Module' on the twin header tank models is essentially a specialised relay where if either of the two inputs are not grounded then the switch is closed resulting in the low coolant tell tale lamp being connected to ground. The inputs are grounded via the probes being immersed in the coolant in the header tanks.

The ecu has no involvement with the low level coolant warning feature.

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That is not my understanding. From what I understand from the service manual the header tanks do control it but so does the coolant temp sensor in the block. It sounds like it goes to the ECU and the ECU can turn the light on for high temps.

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The low coolant tell tale lamp can also be illuminated by the ecu for excessive coolant temperatures via the 'Engine Overheat Relay'. This has nothing to do with a low coolant warning though.

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Thats just the point.. I don't know what is turning the light on, low coolant or high temp coolant. I have pretty much ruled out low coolant in the header tanks so I am looking at the temp sensor now.

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Since you say the warning lamp goes out when you unplug the 'Low Coolant Level Module' then this would suggest the fault lies with one or more of the following:

- the module

- the wiring to the coolant probes

- the coolant probes

- the header tank ground wiring

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Ah ok.. I was under the assumption that the ECU would trigger the same low coolant level module to illuminate the switch. In this case I can narrow it down quite a bit.

 

Thanks!

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There are 3 wires on the header tanks.  One for each reservoir and then a ground wire on the bottom of the large tank.   I'm betting your ground wire came un-done. 

 

Look here at the underside of the large tank on the right

P1010019.JPG

IMG_2796.jpg

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It could be that you just need to rotate the probe in it's grommet (so that the electrical connector is facing a different way), this cured the same issue on mine. 

 

Ged

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Ok, so the light came on and stayed on until I got home today. I checked all 3 connections on the header tanks and all 3 were secure. I then removed all 3 and the light stayed on. I then tried grounding all 3 and the light stayed on.

 

So what activates the low coolant module? Is it a ground signal being introduced at one of the sensors in the header tank? If so, should disconnecting all sender wires from the header tank deactivate the low coolant module?

 

Or, does the module activate when ground is lost on any of the header tank sensors? If so, shouldn't the light come on if I disconnect one of the sensor wires from the header tank? When the light is not on, I can unplug any of the sensor wires on the header tank and the light does NOT come on.

 

Next I will try grounding one of the sensor lights when the light is not on and see if it makes it come on.

 

I can only imagine that the low coolant module may be faulty. Does anyone know if it is just a normal 12volt relay? The pins look like it.

 

Thanks

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Alright, so that module is not just a relay. I cracked it open and see that it is solid state and has circuitry inside. So I have no way of testing it. I found a couple places that have the same part number listed online (B082M6275F

) , mostly Elise parts places. I also found one website that indicates it is obsolete and the picture they show looks nothing like my module. http://www.thelotuscentreonline.co.uk/Module-Low-Coolant-S4

 

Anyone know where I can get the correct part?

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What does yours look like? Mine (SE) looks like the one in your link, and if your VIN number is lower than 1142 it should be A082M4825K, not B, and there should be two of them.

Edited by sanj

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Here is what mine looks like. Disregard the lines where I cut it open.

post-436-0-71191900-1366497495.jpg

Edited by Techspy

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Interesting. Clearly there's a big difference between the 'A' and 'B' parts, not that that's much help to you. :(

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Yeah, according to the service manual the twin header cars came with 2 different setups. The twin modules and the single, which I have.

 

Ok, so for now I just have the module unplugged. Does anyone know if the module controls anything other than the low coolant light from the header tank sensors?

 

Thanks

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The way I interpret the diagram, removing the module will not affect anything other than the coolant level warning function. The ECM can still trigger the warning light via the engine overheat relay if the engine overheats.

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Yeah I gathered it wouldn't cause issues with anything else but there is one post somewhere I read that said it controls other things but it didn't say what. I have it disconnected and haven't seen any other issues. I am trying to find a replacement in the mean time.

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The Corvette module is a single input unit. You could probably rig up two of them and a relay to emulate the Lotus module.

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