Technical Strange temperature gauge behaviour

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Technical Strange temperature gauge behaviour

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May 19, 2006
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Location
Tonbridge, Kent
Hi there

I've a new FIAT - a Brava 100 16v auto, unusually with air-con. Registered May 2000 on a "W", built Feb 2000 according to ePer.

Rather odd goings-on today after sitting in traffic - the temperature gauge shot up from its usual mid-point to nearly the end stop - too quickly to be reporting actual overheating. Accompanied by the idle speed going up to about 1300 rpm every now and then about the same time. Fan cutting in and out in what seemed to be a normal-ish manner (though maybe a bit less frequently than I would expect - but don't know the car very well yet). Switching off and on again would cure the gauge problem for a while, with it going back to its normal mid-point immediately. And no evidence under the bonnet of any actual overheating going on.

I presume this is a coolant temperature sensor problem (intermittent shorting perhaps), with replacement being the solution. Am I right in thinking my car only has one for both the gauge and the ECU, and that the rad fan is switched via the ECU (or is there a separate switch for the fan - though I can't find one...)? Also presume I can just switch the sensor with the ignition off, and don't need to worry about resetting the ecu, or allowing it to do some self-learning routine?

Any comments gratefully received...

Thanks!

Nick Haigh

Stilo 2.4 20v Prestigio
Brava 100 16v auto
Rochester, Kent
 
yes it sounds like the coolant temp sensor may the problem. by the sound sof it the connector is more likley to be the issue here, check it is clean.

you are correct there is only 1 sensor used for both gauge and ecu.

the rad fan is switched by the ecu using a relay on the front of the battery tray. judging by your description this is working ok, so dont disturb it just yet. :)

you can change the sensor with the ignition off, no need to disconnect battery to reset ecu.

the sensor is fitted to the thermostat case. if you remove it you will lose some coolant. that means you will need to bleed and top up the cooling system after.

i would not replace the sensor so hastily, it sounds more like a wiring problem.
 
Thanks jug - helpful. I'll have a go at the connector first. Incidentally, I presume the engine managment ecu also switches the cooling fan when the air-con is on? This seems to be working fine. Or is there a separate aircon ecu?

Nice HLX by the way. I looked at one of those but sadly it wasn't quite as described in the AutoTrader ad. And the wife wanted an auto - so Brava it was! Nice car though - great looks, and possibly the best ride/handling balance I've ever experienced. Why didn't they sell more?!

Cheers

Nick
 
dont even get me started on the twin cooling fan arrangement on models with air con. i've written a 'brief' description of the set up and a method to diagnose fan faults and there is a wiring diagram and a diagram to show where the components are on the car.

https://www.fiatforum.com/bravo-brava/97746-bloody-bravo-2.html?p=1052302

basically there is a second fan on models with A/C, called the high speed fan, and this is switched on seperately to the normal cooling fan. there is no A/C ecu, but there is a nasty arrangement of relays, connectors and god knows what else, so the possiblity for faults is pretty endless and its a bit of a headache trying to understand how it all works.

as for why the bravo/a range didnt sell better, well i think thats mostly to do with the fiat badge. its no secret that fiats can easily give you hell and cost you a fortune (take your pick from rust, electrics, bad materials, shoddy dealers etc etc). now that bravo/as are so cheap, and have proven to be more reliable than your average fiat, they are becoming competitive again and are a popular used car.
 
Gulp - had a look at your piece on the fans! After further experience of my little problem, my engine cooling fan is behaving oddly. When the temp gauge throws a wobbly and goes into the red, the cooling fan typically does not cut in. But if I switch off then immediately restart the engine, the temp gauge goes back to normal and, very often the engine cooling fan cuts in straight away. I hope this behaviour is consistent with a dubious coolant temp sensor (or its wiring) and is nothing to do with the two fans arrangement...!! Incidentally, fan operation prompted by the aircon seems to work fine (doesn't sound like a different speed though...)

Anyway - won't worry about this just now!

To get to the coolant temp sensor on my 1.6, I need to remove the ecu. I know how to do this (I have the Haynes manual), but is there a special procedure for getting the ecu to relearn when it's all connected up again? E.g. starting up and leaving well alone for 20 mins (seems to be one method I've heard)?

Thanks for you help so far....

Nick
 
in the long run the ecu will relearn regardless of what you do, it is constantly adjusting its stored values. however there are things you can do to ensure the ecu relearns your operating parameter more quickly, meaning you will achieve better mpg more quickly. let it idle at least until the rpm drops back to the normal warm level (850rpm). then take it for a short drive around the block without giving it any abuse. then it is given a good start to the learning procedure. but ultimately it makes no difference.
 
Jug - thanks for all your advice. I spent a bit of time on Sunday afternoon taking the ecu off and cleaning up (and/or "working" several times on and off) all the relevant connectors I could find (CTS, fan, those relays ahead of the battery tray which sure enough were a bit mucky). All back together again and so far, seemingly, so good...... (fingers crossed, touching wood etc etc)

Managed to shear two out of three of the rather dubious fasteners holding the front ram air duct on though. I bet I'm not the only one.

Nick
 
mine stays at 90 most of the time. turn off engine. wait 5 minutes or so. restart. goes way beyond that ( 110+- ) when i restart. i noticed that my fan used to continue running even after turning off engine, but no more.

and what's this i hear about 2 fans on air-conned Voes? had a peek underneath and noticed that i've got a missing connector at the motor of the fan positioned near south.

is it by any chance supposed to be connected to 2 wires with light green sleeves?
 
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