coolant temp sensor what does it do?

i own a mk3 golf gti 8v, and i have quite bad mpg someeone as said it could be the coolant temp sensor, but what has coolant temp have to do with fuel?, r they expensive to buy?


thanks.

 

About 25. They seem to have some impact on ignition advance curve, I have yet to findout what else

 

They also control warm up. A lot of the time, when your temp sender goes, you engine will always "appear" cold to the ECU, which means it will chuck in more fuel than is necessary.

 

thanks for that info, have just found a webpage and will paste onto here what a cts does for future referance.
When the engine is cold, extra fuel is needed, and, just as the choke on a carburettor enriches the mixture by reducing the amount of air taken into the engine, the coolant temperature sensor signals the ECU to hold the fuel injectors open longer when the engine is cold, supplying more fuel to the engine.

The temperature sensor is located somewhere in the cooling system, normally near the thermostat housing but not all ways. As the coolant warms the sensor the resistance of the temp. sensor reduces and there for the voltage signal that the ECU is receiving increases and the extra enrichment is reduced, until the engine is at normal operating temperature. This is called a NTC (negative temp. coefficient) sensor and is commonly known as a thermo-resistor,
Common MOT emission failures are caused by this sensor and are normally accompanied by a hard start, this is because when the sensors fail they normally all ways either indicate a permanent cold or hot scenario, causing either too much fuel on hot starts or not enough for cold starts.

 

Thats what i said!

 

Anyoine know the range of resistance readings between hot and cold please?

 

Oh and also what the four connector pins are for those of us who have four?

 

It`s essential to have a good CTS, mine uses twice as much fuel cold as it does hot. I wouldn`t bother testing the old one, if there`s any doubt change it as a matter of corse. Even if it reads ok without the ecu load it could still missread when connecoted to the ecu.

Normal vw NTC`s read 6000 ohms 0 degrees and 200 ohms at 90-100 degrees c.

The 2nd set of pins are probably for the Temp Guage?

 

I changed mine yesterday, but i'm not sure if i got the right one. It is a mk3 16v (ABF) and the sensor i changed was in the black plastic housing on the gearbox side of the cyl head. Couldn't see another sensor anywhere. the one i took out was 2 pin, white and the one i replaced it with was 2 pin, blue. is this the right one (i meant to change the ECU sensor)

 

Wow Neo!
Where did you get this data from. I'm struggling to find out digifant data?

 

digifant data

i have a digifant system pdf file that was used to train the vw mechanics. if you pm me i will send you a copy via email

cheers

rob

 

Aaaagh @Neo - YOU ARE THE MAN!
Why is this stuff not in the Haynes manual? To protect the VW agents?

Thanks man. You saved me plenty $$$'s.

My problem was my wife's Golf was hard to start when cold and had to idle for a while before it was driveable.
On measuring between pin 1 and 3 with a multimeter in the morning stone cold it told me the resistance was sitting at 1K4 (about 35 degrees)!
Replaced sensor for a couple of bucks and all good.

Still peeved it's not in the manual - it is now. I printed out this whole thread and taped it in to my Haynes for future reference.