View Full Version : IS there 2 CTS or just one?

06-06-2010, 11:00 AM
HI, i was wondering if anyone would know this. I am wondering if there are 2 coolant temp sensors on 2001 audi a4 1.8t
I know of one which is located towards the back of the engine, sort of near the battery side but i was just looking under the hood and i realised there is sort of similar sensor clip when i follow the coolant tube which sort of leads towards the radiator it is connected to a bigger tube and it looks to be blue?
anyone know what this is?


06-06-2010, 02:21 PM
The green one at the back of the head is the Coolant Temp Sensor. It has 2 internal sensor circuits, one for the ECU and one for the gauge cluster.

The similar looking blue unit in the lower rad hose, is the "dual thermal fan switch". It is just a switch, not a sensor. One set of contacts closes at lower temperature to operate the electric cooling fan's low-speed. The second set of contacts closes at a higher temp to operate the high-speed.

Interestingly, the connectors and general shape of the units is almost identical, such that they can be physically swapped. This causes problems. So remember, green one at the back of the head, blue one in the lower rad hose.

How I know this...check out my thread on the subject (w/pics!):