Ok, lets get my problem out of the way first - temperature gauge is very intermittent, goes up to 90C then can drop back down all the way. Then back up, then down etc etc. Some days its fine & doesn’t show any signs of there being a problem. But, VAG-COM has listed this as a fault so I’m pretty sure it’s a faulty sensor.

 

So, I go to change it. Get the new sensor from here: https://www.eurocarparts.com/ecp/c/Audi_A4_2.0_2002/p/Car-Parts/Engine-Parts/fuel-and-engine-management/engine-management-sensor/?223440211&1&dd6a12e5bc9e7bc4b5164fada284c88d71054b28&000572

 

Check the internet to see where its location is & found this handy guide:

http://www.emmerium.plus.com/non-site_stuff/FabCoolantTempSensor.pdf

 

Now, halfway through fitting it, I realised that it wasnt the Coolant Temperature Sensor, but the Fuel Sensor! To make matters worse, I dropped the old one I took off into the engine bay so I fitted the new one as it seemed to look & fit identically.

 

So, my question is this:

Firstly, is the Fuel Temp Sensor the same part as the Coolant Temp Sensor? Which, if it is, I'm ok to leave the one I got from ECP in.

Secondly, where the heck is the Coolant Temp Sensor?

 

Cheers.

Coolant temp sender is on the rad hose coming up right side of the engine.  Fuel one is on the fuel line.   They probably are the same part in essence.

Yeah, very embarrassing. Wasnt even thinking when taking it off & only realised when diesel came out & not coolant!!.

So, leave the new sensor in the fuel line & buy another one for the coolant.

Edited 11 December, 20178 yr by Chris Berry

Find the sensor that you dropped, and read part number off it (on the edge of the metal bit where it crimps over the plastic part, I think.)

May be the same as the coolant one, may not be.

 

I think all Fabias use coolant temp sensor part number 06A919501A. Fuel temp sensor appears to be sold pre-fitted to the little hose 'T' and that whole assembly has a different part number.

Edited 11 December, 20178 yr by Wino

Firstly what engine do you have and how old. If it is a 1.4 MPi then do a site search as there loads on how to replace the thermostat and sender unit. Again on a 1.4mpi it's easy to just replace the whole unit in one go. 

 

If your temp guage is going up and down it's probably not the temp sender,  it's going to be the thermostat. The sender only sends a signal to the guage to say how hot or cold the coolant is. The reason it goes up me down is because the coolant is warming up then cooling down. In my experience of over 26 cars, when a sender is unit is broken it will either not work at all or stick at one end of the guage. 

 

The sender in the rad on most cars is the thermostatic connector that controls the fans and not the gauge. If you bridge it out the fans will come on but the gauge will remain the same, or show the cooling effect of the fans.

 

As for diesel, I'm sure the that the temp guage is set up as i say above. I think most diesels have a sensor around the filter as they often have oil filter coolers built in to the housing, but this wouldn't effect your dash temp guage.

 

Hope this helps.

Edited 13 December, 20178 yr by TripleMcB

My temp gauge was going up and down and it turned out to be the coolant temp sensor and not the thermostat

I swapped the coolant temp sensor over 2 years ago and its been fine since.

 

I agree with DC2990 on this. The thermostat regulates the engine temperature & should keep it at a steady 90C when running. A faulty thermostat would either be stuck open or closed which would result in the engine running too cold or too hot.

My symptom is that the temp can be reading 90C (needle straight up) & within 5 seconds go to zero as if the engine has been switched off. A few seconds later the needle will return (fairly quickly) to 90C. Now unless someone switched my normal coolant with liquid nitrogen, I'm 99% certain it’s the coolant temp sensor.

 

Managed to retrieve the fuel sensor & the code on it is '269416'. After much googling(!) I couldn’t really find a reference to it being used for as a fuel sensor only, but a few references of it being used as a coolant sensor. So, my line of thought is that the fuel sensor & coolant sensor are the same part & are interchangeable.

 

Compare the resistance of each at a given temperature, for a rough and ready clue as to how similar/different they might be.

i.e. leave the retrieved sensor outside in the car overnight and compare resistances in the morning.

This thermostat from my fabia gave exactly the same symptoms as the original post. As you can see it would still function but then would allow the engine to cool within seconds even when driving. 

I wasnt saying that you were wrong.

In my case i wasn't 100% sure but for the price and time to fit i decided to go with the sensor.

1 hour ago, DC2990 said:

I wasnt saying that you were wrong.

In my case i wasn't 100% sure but for the price and time to fit i decided to go with the sensor.

 I know, did the sensor fix the problem? 

Because of the weather, working & Christmas shoping, I've not had time to fit the sensor. But as soon as I do, I'll post an update.

Got it sorted last week. Not too tricky, just had to take the top of the air filter off along with the air inlet pipe for ease of access. 

In the end I replaced the fuel temperature sensor back with the original one and replaced the coolant one. Temperature needle now reading correctly and not fluctuating at all.