: 2005 transmission fluid change/check

06-24-08, 12:27 PM
I just picked up a 2005 STS with the NS V8, pretty sweet machine. I realize there is no transmission fluid dipstick to check the level, so how do you check it? The Owner's Manual says have your mechanic check it when in for service but I like to check this and the rear differential myself. Same question on the rear differential, I assume it's like any other, there's a fill plug and you stick your finger in to test the level, right?

On the tranny, does anyone recommend doing this themselves? On all my other GM cars, I usually pull the tranny fluid cooling line off at the radiator and pump out 1 gallon at a time, refill and do this 3 times, I usually don't mess with the filter since it's only a screen and doesn't need to be changed but once every 100k miles.

How often should the tranny fluid be changed? My old 98 Deville was 100k. Any advice is greatly appreciated, thanks!

06-24-08, 02:46 PM
Ask the dealer.

06-24-08, 10:09 PM
Here is a link to a previous discussion on the subject.


06-25-08, 05:02 PM
Thanks much, looks like the answer is there.

10-10-10, 05:46 PM
I was going to drain and refill transmission today but the refill plug (which is on the left (driver's) side above the rear part of the pan) is difficult to get at. A torx (or Star Key) is needed. I stumbled on this torx wrench made specifically for Cadillac (http://www.handsontools.com/Kastar-6532-Cadillac-Socket-Head-Drain-Plug-Wrench_p_6410.html), which looks to me like it might work to get at the 2005 trans plug though it says it's for use on 2003 - 04 Cadillac 3.2L CTS. There is about 1.25 inches of space between the transmission and floor pan, which is where the plug is. Also, the exhaust pipe is right smack in the way, so the wrench I linked to above will likely not work unless the exhaust pipe is at the very least loosened to move it out of the way. There is an exhaust flange about a foot and a half up from where the plug is. If the pipe only has to be loosened then it may be worth the time and effort to change the fluid. Otherwise, pay the $200 and bring it to a Cadillac dealership and save dealing with being on your back and aggravation of dealing with another dumb GM design issue. The only way to get around dealing with the exhaust is to fabricate a tool by welding the appropriate torx to a flat piece of steel, making sure the tool is the lowest profile possible. Then the flat steel could be bent as necessary to avoid the exhaust pipe and should be strong enough to loosen the plug.

10-17-10, 10:36 PM

Today I decided to change the transmission fluid through the pan drain plug since it's difficult to get at the refill plug. I took one of the clear storage containers that you can buy at Walmart for $3-4 and marked it with a permanent marker at 1 and 2 gallons so I would know how much fluid drained. I drained about 5-6 quarts. To loosen the pan plug a T-47 torx a/k/a Star Key is needed. I also tried to determine the size of the Star Key needed to get the refill plug off, but because there was not enough room, I couldn't actually get a Star Key on it. But it was a little smaller than the pan, so I believe it must be a T-45, which matches the tool I linked to above.

Anyway, I pumped fresh fluid in through the pan and all is well. I don't like this process because obviously the ideal way to do it is to refill through the proper plug. It looks like the plug transmission plug threads are the same as the motor oil plug, which is 12mm by 1.75 thread pitch. The best way to pump fluid through the pan is make an adapter where a hose can be connected to the cap of the gallon of fluid and another hose is on the inside of the gallon that reaches the bottom. This way the gallon can be closed tight to avoid spilling and the hose that reaches the bottom will assure that all fluid is pumped into the transmission. This time I did not do it this way, but if there is a next time (which I doubt), I will make an adapter. The next time I will do it the right way.

12-22-10, 10:01 AM
secure the STS on jacks. go to the tanny lines connecting to the radiator(tranny oil cooler) Disconnect the incoming line. start the motor, keep in park. Measure the oubound carefully in a container, run for about 1 minute (=gallon). reconnect the incoming line. disconnect the outgoing line, run a rubber hose to the container of your fresh fluid. You may not get 100% of the fluid, but replacing 4qts every maintenance interval is very easy, with no mess. You can also connect and reconnect the lines on the tranny housing, which ever is easier for you. This is something picked up over the years. On a manual trans I am able to run flexible poly along the firewall, and pull the top plug on the trans insert the poly tube, and use a funnel and pour from the top. (manual trans)

12-22-10, 11:15 AM
What is the advantage of changing tranny fluid before 100,000 miles on the STS unless you are abusing the transmission daily??? To me, when you open the close system you are introducing contaminants into the system. I have never change transmission fluids even on the system with the dipstick.

12-03-14, 12:05 AM
On the passenger side of the transmission there is a pressure sensor that you can disconnect and remove with a 7/8 wrench comfortably here is a link to the Gentleman who suggested this. http://www.cadillacfaq.com/faq/answers/transchange/

I hope it is the same type of transmission.

12-03-14, 10:41 AM
GM found that a major source of transmission problems was maladroit owners introducing crap into the transmission while pursuing DIY service under primitive conditions. The newer tansmissions are assembled in a clean room and sealed with the intent that a misguided owner should not fool with it and have professional service at 100K mile intervals.

12-03-14, 10:47 AM
FixCTS, ???? This thread was dead for 4 years.

You might want to set your profile post/thread view preference to "view latest posts/threads first" rather than wade through old, dead history.

01-27-16, 11:26 AM
Being a mechanical engineer, I don't agree about the contamination issue. There is a filter on the oil pickup in the pan. About a year ago I had my 2006 STS V8 transmission oil cooler fail. A shop fixed everything, but after that on cold winter days until warmup my shifts were soft and I had some engine run-away. TCC engage was harsh too. I had originally chalked it up to some engine coolant in the transmission damaging the clutches (even though they had flushed everything after the repair).

On a recent trip to PA from MI, I noticed engine run-away on some hills even when warm. Based on that I decided to add some fluid to the transmission in case it was low. Using the proper side plug I added a quart and saw a marked improvement. I added another quart and it runs perfetly now...no more symptoms! I believe the shop must have added back insufficient fluid from the earlier repair, and it has been sucking air for the past Year! (and this car has 180,000 miles on it) Doesn't appear to have damaged anything at this point, but I sure wish there had been a dipstick to check the level sooner. I'll probably add another quart or 2 based on the fact that sucking air means the pan was just about empty, and it holds 5 quarts!

The way I added fluid was to park with the driver side uphill then use a ramp and jack to tilt the car even more. That way I could add more fluid without it running back out. The normal service method of topping off fluid is just crazy and impractical (although I did do it once in the past). You must have the engine running at temperature on a hoist remove the plug, pump fluid into plug till it runs back out, then re-install the plug...meanwhile you're burning your hands on the exhaust.

The other thing I did this time is to get a 45 torx bit and wrap a layer of packing tape on the outside so it fit tightly in my small 10mm ratcheting monkey wrench (it's too tight to use normal socket wrenches). That made a handy tool for removing and installing the plug. I can add a quart of fluid in under 10minutes this way. At first I was worried about over filling the transmission, but when you add thru the side fill port I believe it's impossible to overfill, even when tilting the car.

...at 60,000 miles

...at 180,000 miles