Okay, I'm going to try and list everything I can think of that is wrong and what I have recently done. Hopefully this gives you guys a way to tell me what might be wrong. Here goes...

2005 QX56 255k miles

It's been fine for the past 3 years I've owned it. I run full synthetic in it and I change the oil every 5k miles. Just recently I've done new front shocks, new universal joint for driveshaft to front diff and new front pads and rotors slotted and drilled.

About 3 months ago the gauges started flickering or turning completely off when the lights are turned on. I was told it needed to be rebuilt. I have been dealing with it because i don't really drive at night so it was not a bother to me.

Here's the problem, yesterday I started get hard shifts from 1st to 2nd and sometimes it will just make it into 3rd. It also will not go any faster than 40 mph. Once it hits about 41 or 42 it will do this cluck like something is holding the trans. I believe its some sort of limp mode but I'm not sure. I have no check engine light. Although when it happens, the lights that do come on are just about every light that seem to have something to with the trans. The brake light, the 4wd light (the small suv in the gear indicator disappears), the VDC light, the ABS and the cruise light all come on when it goes in to this "limp mode". If I shut if off while its like this it won't start. It will turn over but will not run. I disconnect the battery for about 10 mins or more and it seems to reset what ever the problem is because the truck will run and drive normal. After about 10 to 15 miles it goes back in to this mode. I've checked the fluids and all are fine. Almost forgot, all the lights are out on my dash so the radio lights don't light up as well as the headlights don't go up and down when starting or with the adjusting switch.

I think I got everything that y'all might need to know to help me out with some ideas on where to start with this.
Thanks guys.

Replace your ECM relay and see if that helps. Sounds like it's dropping out and sending the ECM into la-la land. It's a known issue on Titan/Armadas from that vintage, so I presume your QX56 will be similar.

VStar650CL wrote: ↑

Sun Aug 29, 2021 4:50 pm

Replace your ECM relay and see if that helps. Sounds like it's dropping out and sending the ECM into la-la land. It's a known issue on Titan/Armadas from that vintage, so I presume your QX56 will be similar.

Thank you I will give that a try and see what happens.
I also did a little looking after you informed me of the relay and found out that I still have the old ipdm so if that does not solve that problem I will go with swapping the ipdm too.

VStar650CL wrote: ↑

Sun Aug 29, 2021 4:50 pm

Replace your ECM relay and see if that helps. Sounds like it's dropping out and sending the ECM into la-la land. It's a known issue on Titan/Armadas from that vintage, so I presume your QX56 will be similar.

I swapped out that relay and it has been running great. The problem is gone. Thanks for the help.

You're most welcome. Happy motoring!