yariks

Hello,

I had a warm starting problem, so just tried to replace ECT on my 99 2.8Q as described in
https://forums.audiworld.com/a6/msgs/456952.phtml,
but the sensor I pulled out had different harness connector and was blue. The part number on it is 078-919-501B, instead of green 059-919-501A.
So, are there a second one on my car or they just changed it in the middle of the year? Then why price is so different $5 for green one and $30 for the blue?
Thanks.

por911

1)Green(ECT) Sensor located on the backside of the motor. Probably the best $5 spent. I found the new unit in our 30v really improved MPG and idle.
2)Blue(coolant fan) sensor is located on the lower rad hose. No one replaces(or rarely does)that sensor, low production = higher cost. The ECT has been known to be fualty , so I think Audi keeps cost low and its a single circut. Hope this helps.

daschwa

I had the same experience as you mentioned. My temp. sensor is located behind the engine, just as described in the writeup you posted, however, I was disappointed to find that I had had a blue temp. sensor that could not be replaced by the green one. I purchased the green sensor from ecstuning.com, which claimed it was valid for my car, but after removing the old sensor and observing that it was not a match I called the local vw/audi dealer they asked for my VIN and then provided me with the appropriate $35 blue sensor.

AudiForYou's 2.7T

Your car should have both. Look harder.

yariks

The blue one I pulled out, is located in the same spot as the green supposed to be - behind the engine, not on the radiator hose. It looks exactly as the green one, but connector is 4-pin square, instead of oval.
I just got new one from the dealer - and part number is almost same 059-919-501, except there is no B. So I guess they changed the sensor in the middle of production.

I will try to look at my fan sensor and compare.
Thanks.

AudiForYou's 2.7T

On the 2.7T they are both behind the engine, one on each side. Not 100% about the 2.8.

KellerA6

Remove the tray that is located just on top and in front of the intake plenum. It has several vacuum hoses on top and about 3 electrical connections. It's attached to the intake and the top of the engine with 3 10mm bolts. If you remove this and just scoot it out of the way towards the drivers side, you can fit your other hand down in there to help take out and re-install the sensor. You can also see a lot better

urban_legend

Any photos or links for the A6 2.7 twin turbo placement?
I need to replace my coolant temperature sensor.