2008 Hybrid Yukon Sound when gas is applied

[Joelbbvette]

My 2008 Yukon Hybrid has just over 100K. Started doing the following and looking for help. When first starting, have to wait for transmission to build pressure before truck will move forward. Also under constant acceleration or gas is applied, getting a warbling sound that might be coming from transmission pump. Basically goes away after removing pressure from gas pedal. Any suggestions appreciated.

 

[j91z28d1]

I'm no transmission guy.. but have you checked the fluid and do you know the last time the fluid and filters were changed?

on the hybrid side. have your tried driving it in M4 mode and see if it acts the same way? these have an electric pump that runs when the engine is in auto stop and there's some tsb's about them and upgrade done along the way. but if the engine is running, that pump isn't used.

there is a gauge port on the side of the tranny that you can put a mechanical gauge on to real line pressure. I've never done it, only saw it in a manual. I've not found anything on any scanner that shows line pressure.

 

[Zylin]

My 2008 Yukon Hybrid has just over 100K. Started doing the following and looking for help. When first starting, have to wait for transmission to build pressure before truck will move forward. Also under constant acceleration or gas is applied, getting a warbling sound that might be coming from transmission pump. Basically goes away after removing pressure from gas pedal. Any suggestions appreciated.

Joel,

Any updates? My daughter has our 2008 and is describing the same thing.

Thanks

 

[j91z28d1]

just some info I had saved for someone else.

but honestly, if you haven't, always check the hybrid battery condition first.(meaning log cell voltage under load) these batteries were designed for a prius and just added some extra cells for higher voltage. the cooling isn't up to the weight of the truck and it's old school nickel metal hydride battery chemistry. wasn't very good when new. throw in they still have most of the standard problems the gmt 900s are know for, they can be a bit of a hand full.

since their aren't any good mechanics these day, only parts swapers, and these trucks are actually time consuming to troubleshoot. most people have bad luck at shops with these.

 

[BG1988]

My 2008 Yukon Hybrid has just over 100K. Started doing the following and looking for help. When first starting, have to wait for transmission to build pressure before truck will move forward. Also under constant acceleration or gas is applied, getting a warbling sound that might be coming from transmission pump. Basically goes away after removing pressure from gas pedal. Any suggestions appreciated.

AUX transmission pump... most likely