IMS Internal Mode Switch

[Jake707]

My wife’s 17 Yukon Denali 6.2 has been struggling with random “service stabilitrack” and “shift to park” errors even though it is in park for awhile now. When this happens the power and throttle response are cut back and it won’t let you turn the car off because, I assume, thinks the car is not in park. Usually it will clear itself after sitting a min or two, sometimes she has to drive it around the neighborhood a few times before it will clear. There is never a remaining check engine light or code after so it was hard for the dealership to find the issue.

First the dealership diagnosed a faulty wire harness in the trans and it was ~$2k fix which lasted all of about 2 days before the errors came back.

Now they are saying it’s a faulty IMS or internal mode switch and that repair is also $2k. Anyone have any experience with these going bad or know how to replace them? I found a video on a 6 speed but not sure it’s the same as I believe mine is the 8 speed. I’m comfortable pulling the pan but if I need to remove the valve body assembly I’m nervous some random check balls are going to get lost or something.

 

[Joseph Garcia]

@NickTransmissions has posted videos YouTube on troubleshooting the IMS. I don't know if the transmission needs to be out of the truck tp perform the troubleshooting, and he will let us know.

 

[NickTransmissions]

My wife’s 17 Yukon Denali 6.2 has been struggling with random “service stabilitrack” and “shift to park” errors even though it is in park for awhile now. When this happens the power and throttle response are cut back and it won’t let you turn the car off because, I assume, thinks the car is not in park. Usually it will clear itself after sitting a min or two, sometimes she has to drive it around the neighborhood a few times before it will clear. There is never a remaining check engine light or code after so it was hard for the dealership to find the issue.

First the dealership diagnosed a faulty wire harness in the trans and it was ~$2k fix which lasted all of about 2 days before the errors came back.

Now they are saying it’s a faulty IMS or internal mode switch and that repair is also $2k. Anyone have any experience with these going bad or know how to replace them? I found a video on a 6 speed but not sure it’s the same as I believe mine is the 8 speed. I’m comfortable pulling the pan but if I need to remove the valve body assembly I’m nervous some random check balls are going to get lost or something.

If you have a Denali, you should have the 8-speed 8L90 however the IMS functions the same as the one in the six speeds. The mode switch is integrated into your selector shaft / rooster comb assembly, which is accessible once the pan is off the transmission. There's a small stud on the rooster comb that engages a slot in the IMS so that it can sense range position shifts when the driver works the gear shifter and communicate that to the ECM and other modules on a 'need to know' basis.

You should be able to drop the pan and remove/reinstall an IMS yourself if you have a level workspace where you can get the vehicle up in the air, safely on jack stands.

Here's a picture of an 8L90's underside w/the pan off - the IMS is by the gear selector about 2 inches to the right of the 1-2-3-4-5-Rev Boost Solenoid, which is at the bottom-center of the image. Note the recangular-shaped tan plug - that's the internal mode switch's connector.

 

[Jake707]

If you have a Denali, you should have the 8-speed 8L90 however the IMS functions the same as the one in the six speeds. The mode switch is integrated into your selector shaft / rooster comb assembly, which is accessible once the pan is off the transmission. There's a small stud on the rooster comb that engages a slot in the IMS so that it can sense range position shifts when the driver works the gear shifter and communicate that to the ECM and other modules on a 'need to know' basis.

You should be able to drop the pan and remove/reinstall an IMS yourself if you have a level workspace where you can get the vehicle up in the air, safely on jack stands.

Here's a picture of an 8L90's underside w/the pan off - the IMS is by the gear selector about 2 inches to the right of the 1-2-3-4-5-Rev Boost Solenoid, which is at the bottom-center of the image. Note the recangular-shaped tan plug - that's the internal mode switch's connector.

View attachment 458131

Thanks @NickTransmissions . Will it come out without removing the valve body assembly? If I do myself is there anything else I should replace with it, the part that plugs into the IMS for example? Do you happen to have the part numbers I would buy too?

 

[Jake707]

Our extended warranty ended up covering the repair and so far the issues haven’t come back. Knock on wood.

 

[Imup5-0]

Our extended warranty ended up covering the repair and so far the issues haven’t come back. Knock on wood.

Im having the same problems with my wife’s 15 Denali. Was it the ims the dealer changed that ultimately fixed your problem? From my research this seems to be the culprit. I cannot find a good part number for the switch. I would definitely be able to change it myself if I can find the part number.