Topic

Oops! Didn't spot the mems 2 in the original post but I. agree with James that it would normally be a mems3 at that year, 2001.

Yeah it’s a very late MGF on a Y reg but doing research it’s before the VIN cut off for the swap to MEMS3.

Plus I already tried a regular mechanic scanner that communicated with my ZR fine but won’t with the F

If you look at the top of the ECU through the inspection hatch is it rectangular or wedge shape.

So... update.

I removed the sensor and tested it on the hob with a multimetre and the resistances seemed ok and what I read online.

I also cleaned the sensor plug and socket with electrical contact cleaner. Reassembled and put carpet back etc

Gone out for a drive about 6 miles and park up for a mo. Gauge perfect and “normal”. Fan not running.

I then go 100 yards and stop at the junction and hear a wirring. Get out and check- yeah the front fan is on. I thought I would give the benefit of the doubt and see if it goes off.

Done my 6 miles home at speeds of up to 60mph on clear roads and fan still wirring.

Get home and totally switch car off and then back on to ‘reset’ the system, and the fan started back up as soon as engine did.

So it was triggered needlessly and doesn’t switch off??

Okay so been out to the car on my driveway and started briefly to see if fan’s come back on with engine. They stayed off.

This elliminates the plug coming loose or detached.

Im wondering if this is perhaps not an electrical issue. If sensor reads correctly, it tells ecu, ecu turns fan on and off. There really isnt a lot to go wring electrically. Yes it could be an ECU problem, or perhaps a poor earth. But I would expect to see other issues if that was the case. Remember, the temp sensor is at the engine, so is reporting whats happening there, not at the radiator.... is water actually being pumped efficiently?

when the fan is running check the hoses going in and out of radiator. Is there much of a difference? inlet should be uncomfortable to touch, outlet should be quite a bit cooler. Do not get anywhere close to the actual fan.

do you know history of water pump? they are usually changed when cam belt is first done, but not always.

Have you bled the system at the three bleed points?

Have you checked the jiggle valve, and that you are getting a return into the header tank?

etc...

Hi!

So I contacted my supplier of the most recent sensor and he sent me a replacement.

I installed today and started the car. Ran it up to temperature giving it the odd rev up to help circulation and to test any faulty “triggers” of the system perhaps through movement and the fan cut in and out 3 times perfectly at the “normal” on the gauge. Hooray!!

I then got in the car as the fan was running and drove about 4 miles and it never switched off by the time I pulled up??

When I came out of the shop and restarted the car after it had been sat for over an hour the fan came on almost immediately and didn’t switch off until we returned home.

Bloody mems2 stops me from easily reading temperatures live

Help!

Drove again this evening engine stone cold.

Started engine and no fan, got 1/4 mile round the corner and stopped at a junction and could hear it running.

Something is triggering it off when I drive/ signal to ECU is being interfered.

Hi

Been following your problems with interest.

Not had this issue before but you could consider trying to substitute the tempereture sensor with a resistor and see what happens.

First, when engine is cold, disconnect the sensor and using a multimeter on ohms reading measure across both terminals. Make a note of the reading in Ohms.

Now go on ebay and search for a 1/2 watt resistor of the same value (or as close as possible) to what you measured.

When you recieve it insert it into the plug in place of the sensor. Fan should not be running.

Just had a better thought

Now you have two sensors, disconnect the plug from the one fitted to the car, and plug the other one into the plug. The sensor will now be reading air temperature, and should not trigger the fan.

Now have a drive around, keeping an eye on the temperature (as you should now have no fan running). If the fan has come on then you have either a wiring fault or the ECU is faulty. If the fan does not come on then issue is sensor or water temperature.

Another test would be to buy a variable resistor (potentiometer) which is about 2x the value you measured originally.

Set it so on an ohms range it reads the same as your original measurement for the sensor (about middle position)

Insert this into the plug (using flying leads). You should be able to now turn the fan ON by changing the value of the variable resistor, and turn it off again by returning to the original position (it will not be instant ON/OFF)

Please note I have not tried this before, but I think in theory will help you diagnose the issues that cause the fan to run incorrectly. It would certainly eliminate the sensor or water temperature from the causes. At least you can test (by simulating the sensor) without having to drive around.

Thanks for the advice!!

To be fair, initially when I had the phantom fan operation I sprayed the connector to the sensor with WD40 and rightly or wrongly that stopped it.

Since spraying with ECC it’s reverted back to mucking about.

I’ll definately try your test with the 2 sensors, but I have a hunch there is an issue with the plug for the sensor.

I’m fairly sure it’s not a cooling system/ temperature issue as it triggers after as little as a couple of hundred yards from stone cold sometimes, so impossible for the coolant to be anywhere near hot.

When I couldn’t get the car to idle and it was revving itself up at idle with out me touching anything I cleaned all the throttle body, idle valve and all the usual fixes with zero difference.

Sprayed the ECU connector with WD40- running problem sorted. Weird

If I can throw my observation of your problem with radiator fan.
From my point of view it behaves like at some point sensor connector is disconnected from sensor and then ECM starts the fan as it should when connector is disconnected and it does not stop.
This same would happen if ECM senses too high resistance from sensor side.
All this time up to now you changed sensor, clean contacts on sensor and that would temporary solve the problem but it would come back.
Point is, all this time you did not consider other side of sensors contacts which is at ECM connector side.
It is possible that unplugging connector from ECM and clean contacts there might solve your problem.
Possibility is that contacts in ECM connector develop surface rust and because of that provide high resistance for CTS connection and then get the fan started.

Have you checked end to end continuity from the sensor connector back to the appropriate pin on the ECU?

It's possible that you have a damaged cable, because absence of a voltage from the sensor makes the ECU turn the fan on