Coolant Temperature Sensor A6 2004 C5 2.7T DIY by deem2000

4 minute read

Coolant Temperature Sensor A6 2004 C5 2.7T DIY 

Compliments of deem2000 @ https://www.audiforums.com

1-22-2012

My car threw an MIL (Malfunction Indicator Light), Fault Code 19537 / P3081 and after a bit of diagnosis I determined the CTS (Coolant Temperature Sensor) was in need of replacement. The diagnosis portion can be found in this thread https://www.audiforums.com/forum/aud...gnosis-178478/.

Special thanks to chainm for his DIY http://forums.audiworld.com/showthread.php?t=1693546 which was quite helpful. While this DIY aims to provide enough information to complete the repair you should read that post as well.

Tools
Pliers
Flat head screw driver

Replacement Part Numbers - $40 from local dealer
059919501A – Coolant Temperature Sensor (green)
N90316802 – O-Ring Seal
032121142 – Plastic Clip

Time
30min – 1hr

It’s best to work on this when the engine is cold, ie let it sit overnight. I didn’t spill any coolant as result. I’ve included part numbers where applicable. Sometimes I find it easier to look up a part and from the picture I’m able to figure out disassembly. Each step has an attached corresponding photo.

Step 1 – Get access to the repair
- Open the coolant reservoir to remove any pressure. Set the cap in driver’s seat or with your parts so you don’t forget to tighten this back down!
- Remove the engine cover and air box cover.
- Remove the air tube

Step 2 – Get access to the repair
- Remove the heat shielding material (silver with 2 snaps) 078131745 from the Secondary Air Injection Connecting Pipe 078131831L.
- Disconnect the Secondary Air Injection Connecting Pipe from the Combi Valve 078131102M. This can be tricky at first, but it’s actual easy. Squeeze the connector on the top and bottom and pull.

Step 3 - Replacement
- Remove the Plastic Clip 032121142 by holding on to it with one hand and using a screw driver to wedge it out. Note, the Plastic Clip was already removed in the picture.
- Remove the Coolant Temperature Sensor by pulling and wiggling the sensor back and forth.
- Using a flat head screw driver insert as shown in the picture and pull up. It doesn’t take much force; you might hear an audible click. Pull the Coolant Temperature Sensor away from the connector.
- Remove the O-Ring from the housing if not on the sensor.
- Clean the housing where the O-Ring sat. Admittedly, I forgot to do this, no problems though.

Step 4 – Re-Installation
- Put the new O-Ring in the housing.
- Connect the new sensor to the connector. You should hear an audible click; test it by trying to pull it apart.
- Push the sensor and connector back into the housing, wiggling a little bit until it is seated. See the photo for a properly seated connector.
- Put the Plastic Clip back on. This should go on fairly easily; if not then you may not have the sensor properly seated or you may not have the clip in the slot.
- Put the heat shield material back on the Secondary Air Injection Connecting Pipe
- Connect the pipe to the combi valve.
- Reinstall air tube and covers.
- Close the coolant reservoir (I almost forgot this one).
- Reset the code using VCDS / VAG Com

Good luck!

2004 A6 C5 S-Line 2.7T