Replacing Engine Coolant Temperature Sensor (ECT) - Long
Just replaced the ECT on my 2000 A6 2.8Q. It didn't take too long to replace, with the exception of figuring out how to pull the clip and harness connector out with my *big* hands. If I didn't know any better, I'd think that the assemblers for this car were midgets.
BE SURE TO WORK ON THIS ONLY WHEN THE ENGINE HAS COOLED OFF. YOU CAN SERIOUSLY BURN YOURSELF IF THE ENGINE IS STILL HOT WHILE PERFORMING THIS TASK.
THIS IS INFORMATIONAL ONLY.
OK, now that's out of the way. Here it goes. First, I had to get the parts. The part numbers are:
First remove all covers in the engine bay. Then remove the flex hose that connects the air box to the motor.
Next, locate the sensor. It's located under the solid hose that is connected to the motor. The sensor is mounted on top of a tube coming out of the engine. (See Picture)
Here is a close-up of the sensor.
Here is the tricky part. To remove the sensor, you need to find a way to get your hands in and around the sensor. There is only enough room for your left hand to squeeze through. Twist the connector until you can get either your thumb or index finger on the retaining clip holding the connector onto the sensor. *PUSH* on the connector down as if you are trying to plug it in. THEN SQUEEZE the retaining clip on the connector. Then and only then will the connector want to come off of the sensor. (You need to try this a few times.)
When you get the connector off, put it aside of the sensor.
After taking the connector off, the rest of the job is a lot easier.
You will need to wear rubber gloves and a pan under the car for this. Coolant will get all over the place.
Get a good grip on the sensor retaining clip. It's going to take some massaging to pull it out. The trick that I used is first pull on the clip with my thumb and index finger. When it would nudge out a bit, I would stick part of my middle finger in between the clip and the sensor as a wedge. Then I would relocate my thumb and index finger again to get a better grip. Do this a few times and eventually the retaining clip will pop out.
When the clip pops out, the sensor will be loose to be removed. When you pull the sensor out, coolant will spill out, as pressure in the system will be released through the path of least resistance.
Remove the sensor. Check to see if the O-Ring is still stuck to the sensor. If the O-Ring is not on the sensor, it is most likely still on the tube. Stick your finger into the hole and fish out the O-Ring.
Place the new O-Ring on the new sensor:
Insert the sensor into the hole on the tube. Use the NEW retaining clip and push it around the sensor holder until you hear a "CLICK". Check the sturdiness of the clip by wiggling the sensor.
Reinstall the connector onto the sensor. Make sure the orientation of the D-Clip Backshell is correct. Then push the connector onto the sensor.
The job is almost done. Just need to clean up and reinstall all the plastic covers back on.
Be sure to reinstall the flex hose onto the airbox. It's cooled off and is a bit harder to put back on. Make sure it's sturdy before clamping it back on.
You are now done.
Last edited by Kris Hansen; 04-29-2009 at 03:33 PM.
Reason: added to wiki
Re: Replacing Engine Coolant Temperature Sensor (ECT) - Long
So I did this and replaced the ECT sensor, however I still have the P0118 code : (. One question I had though; is the sensor supposed to wiggle a little bit? I didn't feel like it was installed properly because after I was completed, the sensor is still movable inside the tube.
Something that makes this a lot easier, even with big hands--remove the sensor before unplugging it.
There's enough wire there to manipulate it easily. That made this job really simple. Also, not a drop of coolant leaked out, just fyi. I did release pressure by opening the coolant reservoir to relieve pressure.
So in a nutshell:
1. Remove plastic engine covers: big central one with four "screws", and pull-off one above air cleaner.
2. Remove big flexible air intake hose after loosening two hose clamps.
3. Locate ECT sensor. Roughly 6" beneath the downstream side (smaller of the two air openings) of the air intake hose you just removed. It's a vertical sensor in a horizontal cooling tube.
4. Remove the light grey electrical connector just above the ECT to gain better visual access (pry the metal wire off, be careful not to drop it--it's loose).
5. Remove plastic clip holding the ECT in place, pull the ECT straight up, THEN unplug the electrical connector by twisting a screwdriver against the prong to bend it longitudinally away from the sensor. One you get the right motion, the ECT will unplug easily without much resistance.
6. Remove o-ring from coolant tube if it did not come out with the sensor. It may be hard to see if it's dirty. You'll swear it's not there, but reach in with your finger and it'll come out.
7. Clean surface where o-ring was sitting to give new one a good seal.
8. PUT O-RING IN COOLANT TUBE FIRST (before sensor). The sensor will be hard to push down far enough otherwise.
9 . Push new ECT sensor into o-ring and slide new plastic clip in place. You'll have to push hard. I found it easier to push the plastic clip in place, then push down on the sensor and side to side, so the two prongs of the plastic clipped "snap" into place above the ECT flange. Note that the plastic arms of the clip need to go ABOVE the flange of the ECT, not around it. A very large, flat bladed screwdriver helped apply pressure.
10. Plug light grey electrical connector back in and don't forget the retaining wire.
11. Put it all back together!
Hope that helps... it took me an hour, and I cleaned the o-ring surface very carefully and took my time, so this is really a simple job. If you're thinking about having someone do this for you, I encourage you to try it yourself first!
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