Truck shuts down when transmission hot

Matt Dale · September 21

Hello all seem to be spinning my wheels at the moment. 2018 z71 shutting down not limp mode, when transmission reaches 150 degrees has any one ever had this happen? Wondering if I should do the bypass delete is it suitable for canadian climate any input would be appreciated tia

SeekAndDestroy · September 22

9 hours ago, Matt Dale said:

Hello all seem to be spinning my wheels at the moment. 2018 z71 shutting down not limp mode, when transmission reaches 150 degrees has any one ever had this happen? Wondering if I should do the bypass delete is it suitable for canadian climate any input would be appreciated tia

150 Celsius? Or F? If the trans hit 150 C it’s probably toast.

The “bypass delete” will work in Canada. I ran with the pill flipped for 30000 km here in Alberta. I now have the updated TBV that opens at 70 degrees. Tranny works better when it’s -30 out

Matt Dale · September 22

18 hours ago, SeekAndDestroy said:

150 Celsius? Or F? If the trans hit 150 C it’s probably toast.

The “bypass delete” will work in Canada. I ran with the pill flipped for 30000 km here in Alberta. I now have the updated TBV that opens at 70 degrees. Tranny works better when it’s -30

Yes celsius I'm lead to belive that the bypass failed to open? Not sure what temp the stock one is supposed to. I have only had this issue twice,the first time I was able to roll into a parking lot, dash said idle engine trans hot at this point I knew nothing of the bypass after looking for leaks and a few mins later I shut the truck off and restarted all of a sudden the fans went into hyper drive and the temp came down . Second time similar but without warning on dash fan failed to come on had to let it cool before I was able to move truck again luckily this time I was able to roll In to my own driveway

Matt Dale · September 22

18 minutes ago, Matt Dale said:

Yes celsius I'm lead to belive that the bypass failed to open? Not sure what temp the stock one is supposed to. I have only had this issue twice,the first time I was able to roll into a parking lot, dash said idle engine trans hot at this point I knew nothing of the bypass after looking for leaks and a few mins later I shut the truck off and restarted all of a sudden the fans went into hyper drive and the temp came down . Second time similar but without warning on dash fan failed to come on had to let it cool before I was able to move truck again luckily this time I was able to roll In to my own driveway

Tomorrow hopefully the tranny guy is going to drop the pan, my best guess the torque converter is on its way out? Just really confused because the truck drives fine until just before it shuts down, no freewheel it immediately down shifts also showing a code that loat communication with tmc which I would guess happened when the truck shut down

SeekAndDestroy · September 23

1 hour ago, Matt Dale said:

Yes celsius I'm lead to belive that the bypass failed to open? Not sure what temp the stock one is supposed to. I have only had this issue twice,the first time I was able to roll into a parking lot, dash said idle engine trans hot at this point I knew nothing of the bypass after looking for leaks and a few mins later I shut the truck off and restarted all of a sudden the fans went into hyper drive and the temp came down . Second time similar but without warning on dash fan failed to come on had to let it cool before I was able to move truck again luckily this time I was able to roll In to my own driveway

Stock opens at 90 C. Something is wrong inside the tranny. Most likely torque converter, like you said. If the fans came on and it cooled off, then the bypass valve opened. Just opened too late for some reason.

150 C is way too hot, you probably cooked all of the seals. Probably gonna need a rebuild. If I was getting a rebuild done I would put an aftermarket converter in. They are built better. Also get the 70 degree TBV

mikeyk101 · September 23

Not doubting you but 150⁰c is 302⁰F and I have never heard of a trans heating up that high before. I know one time mine got up around 260⁰F but was being given all kinds of warnings on the DIC prior to that to pull over and stop and leave truck running to cool it down. I thought it went into a limp mode by then as well.

Matt Dale · September 23

7 hours ago, mikeyk101 said:

Not doubting you but 150⁰c is 302⁰F and I have never heard of a trans heating up that high before. I know one time mine got up around 260⁰F but was being given all kinds of warnings on the DIC prior to that to pull over and stop and leave truck running to cool it down. I thought it went into a limp mode by then as well.

The first time was around 250f once I poked around and found out tranny temp was not being displayed and I turned it back on