Is there 1 or 2

Can't seem to get an answer either. On the petrols there's two one at the top of rad and one at the back of the engine. If you have two one will be where I showed you on that pic and the other bear the rad would be my guess. My advice would be for you just to ring a parts department, give them your vin and they'll be able to sort you out with the parts. Otherwise you're running the risk of getting the wrong parts. Or speak to Audi. 

Here's the info on two sensors: 

"There are two temperature sensors in some vehicles, one to send information from the engine system to the control unit and another from the control unit to the dashboard. The device follows the principle of dependence of potential difference in temperature."

Ye thanks will have a look found 1 on the back of the engine block 

8 hours ago, Beany1 said:

Ye thanks will have a look found 1 on the back of the engine block 

My gut feeling says one. 

Is the coolant temp sensor supposed to be green or grey 

 

6 hours ago, Beany1 said:

Is the coolant temp sensor supposed to be green or grey 

 

Looking online.it appears to be grey. Think the S3 had a green one? 

This link might help too: 

https://www.pelicanparts.com/techarticles/Audi_B6_A4/13-WATER-Coolant_Temperature_Sensor_Replacement/13-WATER-Coolant_Temperature_Sensor_Replacement.htm