Car engine fan issue - will it fail MOT?

24
Posted 9th Sep
I understand a vehicle can fail an MOT if the engine cooling fan doesn't kick in when it's supposed to.

My issue is that, due to an ECU fault, the cooling fan is permanently on at its maximum setting. It never switches itself off so every time I park I have to disconnect the battery.

Anyone know if this will cause an issue with the MOT?

Thanks
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24 Comments
Is the Engine Management Light on? If so it's a fail.
Edited by: "Candystore" 9th Sep
What's the issue with getting it fixed by a certified mechanic?
Joshua_Blake09/09/2020 10:24

What's the issue with getting it fixed by a certified mechanic?


Cost - I assume.
m5rcc09/09/2020 10:31

Cost - I assume.


My mantra is, if the cost of the repair is greater than the car, it's not worth the repair. Hopefully someone can answer the question for them though.
Joshua_Blake09/09/2020 10:34

My mantra is, if the cost of the repair is greater than the car, it's not …My mantra is, if the cost of the repair is greater than the car, it's not worth the repair. Hopefully someone can answer the question for them though.


It's probably a thermo switch. Easy fix.
m5rcc09/09/2020 10:35

It's probably a thermo switch. Easy fix.


Also only costing a few £'s to buy.
Plus if the cooling fan is always running the car will not get up to normal running temperature so it's constantly wasting fuel aka money and also it may interfere with the CO2 emissions readings.
Edited by: "PaulandPam" 9th Sep
If you get an engine management light or a temp warning, it's going to fail. Otherwise garages can't be expected to have a detailed knowledge of individual car's cooling systems.
Why can't you just disconnect the fan before you take it for it's mot?
First find a garage that does No pass no fee.
Get there early and let the car cool down, pull out the fan fuse.
Get Mot, put fan fuse back in and away you got.
Without the fan the car will not overheat for 15 mins at least.
bigwheels:
First find a garage that does No pass no fee.
Get there early and let the car cool down, pull out the fan fuse.
Get Mot, put fan fuse back in and away you got.
Without the fan the car will not overheat for 15 mins at least.

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Thanks all...

There's no other issues with the car, temperature gauge is fine, no management light. From reading around, it's a common problem with these cars. Normally it's cited as an issue with the relay but I tried replacing it and there was no difference.

This was diagnosed a few years ago but at that time it was intermittent and would stop eventually. I asked at the time of MOT and they said the fan had come on when it was supposed to so I didn't bother locating a specialist and paying the £250 odd required. Now the car is so old it doesn't seem worth spending any money on it.

In terms of disconnecting the fan, my understanding is that checking that the fan has come on is part of the MOT i.e. ensuring the car won't over heat (I could be wrong?). At a previous MOT I did ask how the fan was and they said it came on as expected. There is a connector to the fan that I can disconnect but it feels very stiff and I was concerned about breaking something if I force it.
Do NOT do as previously mentioned and disconnect the fan fuse, I know my mot garage will drive the car onto the car lift and leave the engine running for the full length of the mot which is supposed to be 45 to 60 minutes.
They do this because the emissions test is done when the car is at full normal operating temperature, you'll end up badly overheating your engine with no fan.
Why not just call the mot garage and ask them what the situation is with the fan before you take it and pay????
Why don't you just ask a garage what the actual issue is, it might be an easy fix. Removing the battery terminals sound a pain in the butt.
Don't remove fuses either, stupid idea!
It'll probably be cheaper to fix than you think, at the end of the day it's your transport and you want safe for yourself or passengers
Candystore09/09/2020 10:20

Is the Engine Management Light on? If so it's a fail.



Easy there tiger, we don't know the year of the vehicle or any other details. We can't go jumping in there willy nilly with a fail, we need to establish some vehicle information first.


Engine malfunction indicator lamp (engine management light or ‘EML’)

Turn on the ignition and check that the engine malfunction indicator lamp (MIL) illuminates and then goes off. On some vehicles it will be necessary to start the engine before the MIL goes off.

You need to inspect MIL fitted to:

  • petrol vehicles with 4 or more wheels, not more than 8 passenger seats in addition to the driver’s seat and first used on or after 1 July 2003
  • petrol vehicles with 4 or more wheels, more than 8 passenger seats in addition to the driver’s seat and first used on or after 1 July 2008
  • gas and bi-fuel vehicles with 4 or more wheels, not more than 8 passenger seats in addition to the driver’s seat and first used on or after 1 July 2008
If I was testing it, It wouldn't interest me if it was running all the time as long as I could get the engine up to temperature for the emission test.

And whilst I'm here, can you click the Matters of Testing. 'Beat the Rush' MOT campaign,if you're due an mot, I'd advise to get it done earlier rather then later.
Edited by: "richp" 9th Sep
Check the coolant temp sensor mine went and fan wouldnt stop running.
richp09/09/2020 13:27

If I was testing it, It wouldn't interest me if it was running all the …If I was testing it, It wouldn't interest me if it was running all the time as long as I could get the engine up to temperature for the emission test.And whilst I'm here, can you click the Matters of Testing. 'Beat the Rush' MOT campaign,if you're due an mot I'd advise to get it done earlier rather then later.


Do you do MOT testing?
Willy_Wonka09/09/2020 16:46

Do you do MOT testing?


Yeah, I'm one of the guys or gals that could make or ruin your day
richp09/09/2020 18:05

Yeah, I'm one of the guys or gals that could make or ruin your day



Messaged you. Oh lord of the garages!
Like has been said already. The fan constantly running isn't an MOT failure, However it may not reach normal operating temperature so that could result in the inability to test the emissions etc.. which would then result in failure.

Could be the radiator fan switch at fault. Sometimes called coolant sensors or thermostat sensors and maybe other names etc.

If it is a faulty ECU then you could mod it and use an aftermarket radiator fan switch that'll turn the fan off and on etc.. Something like this universal thermal radiator fan switch.

If your engine isn't at normal operating temp then it'll hammer fuel economy etc..
Edited by: ".MUFC." 9th Sep
What kind of car is it. Someone might have a quick fix other than that silly £250 quote.

When my fan was constantly on it was down to
This £2.29 part. Radiator thermo switch. If you have something with wires on sticking out of the radiator it could be that sensor at fault. There will be another one somewhere on the cooling system which reads the coolant temp.

41876891-WdCLO.jpg
Get the codes read - hopefully an easy fix - you could wire in a switch
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