jseklund

Sorry, it is the coolant temperature sensor. It is s a green sensor and if you remove the Y pipe on the top off the engine and look down behind the engine you will see a black coolant pipe that goes between the two heads on the back of the engine. The green sensor will be noticeable and will be in the top of the coolant pipe, behind the passenger side head.

KingHamer

Awesome, thank you so much. I'll definitely look into it! Just in case though, the Aux pump is under the y-pipe, and on top of the intake manifold correct? I looked at the DIY, I thought I could see it

jseklund

The Aux pump is under the upper intake manifold. So you pull the Y-Pipe, disconnect a bunch of hoses from the top of the manifold (careful - many are hard plastic that is brittle and will snap if you just look at it the wrong way) - and then you take out about 20 hex-head cap screws and the manifold lifts off. Use a bungee cord or coat hanger to hang the manifold so you don't have do disconnect fuel, etc. and you can work under it.

devinsixtyseven

I put 65K miles on a factory replacement CTS with a clean seat and factory o-ring, and it failed exactly as jseklund described. Coolant made its way past the seal to the body of the sensor, corroded and compromised the brass where it's crimped around the sensor body, caused haywire readings but no codes, and when I removed it to replace with a new one, I pulled out a green sensor body, a probe covered in some pliant material with wires running to the body, and a lot of brass debris. Had to clean it up with q-tips, and remove the brass nose of the old sensor with expanding snap ring pliers.

To get to the CTS...on the driver's side of the silver Y-shaped intake pipe on your BEL block (I assume, being in an 04), there's a small conical rubber boot and heat shield with snaps over a valve, attached to the intake pipe. Remove the little fabric heat shield, and remove the boot. I recommend a pair of picks to help the plastic ring over the flange on the intake pipe...you'll see what I mean. Five minutes of cursing if you try with your fingers, ten seconds with a pair of picks. Then release the spring clamp on the Y-pipe where it joins the flexible corrugated pipe leading to the air filter box, and while you're at it, release the same type of clamp at the other end of that corrugated hose. Loosen both clamps where the Y-pipe meets the rubber boots at the front of the engine compartment, remove 3x10mm bolts, and work the intake pipe out. Next pull the corrugated intake pipe section out, there's a hose underneath it which pops in and out, there's basically a thick o-ring on the bottom of the corrugated pipe.

At that point you should be able to see the coolant pipe and the sensor from the passenger side of the engine compartment, with a flashlight. Your stock sensor is probably black, the updates are green.

*Carefully* remove the small diameter flexible hose from the combination valve on the passenger side of the block, same type of plastic ring snap-together connector as the one on the silver intake pipe, use picks again. Zip-tie the connector out of the way, don't break that hose.

A long bent-tip pick makes it easier to release the electrical connector, since space is limited.

Keep the coolant reservoir closed!

Use a flat tip screwdriver to gently work the retainer clip loose. It comes out pointing roughly at the rear passenger corner of the engine compartment. Don't drop it. Gently pull the sensor out, noting which way the key is facing, so you can align the new one with the wiring harness. Not required, just easier.

Make sure you get the old o-ring out.

Clean the seat. Install the new o-ring.

Back off the coolant reservoir cap slowly, just a little, until coolant comes up to the edge of the clip seat, then close it again. Work the new sensor in to place, install the new clip, save the old clip and o-ring, and put everything else back together.

KingHamer

Alright, so I replaced the Aux pump and the coolant temperature sensor. The original aux pump looked good, in fact I don't think it needed to be replaced at all but I did it so that's done. When I did replace the CTS, the o-ring was completely deteriorated. I replaced that, started up the car, and I'm still dropping coolant like it's a joke!

What I think it is, is the o-rings on the back of the engine where the coolant lines run to the front. below the CTS. I can see water dripping from that region, but its definitely not the CTS. MY real question is, how in the hell do I replace that o-ring? Any tips on how to get back there? If I take out the accordian intake piece and the Y-Pipe, I get some room but not much.. If anyone has any tips, please let me know. Thanks!

KingHamer

Thanks a bunch for this post, it helped a lot. It was a lot easier than I thought it was going to be. That old o-ring was in such rough shape.