08 TAHOE Clunk when hybrid switches to engine
 

Hey guys, on my 08 Tahoe every time I begin accelerating from a stop the hybrid battery switches over, and fires up the engine (as it's designed to do). The problem is, that when this happens there is a loud clunk from the front end of the truck, that can be felt on the floor boards. It feels like it's coming from right under/in front of the brake pedal.

Initially I thought it might be driveline related but I'm unsure why it would occur only when the engine comes on line.

Any ideas are appreciated!

Re: 08 TAHOE Clunk when hybrid switches to engine
 

Same thing with mine. A new thing in the last couple of months. Have pinned it down to when accelerating from a rolling stop when engine is not running, not a dead stop. Feels like the transmission was dropped into drive from neutral. Battery seems fine, it runs on electric all the time and for a mile or two when driving easy under 30. Mileage holding at 19.9 average in town,.

Re: 08 TAHOE Clunk when hybrid switches to engine
 

Yeah sounds just like mine... I feel my hybrid system is running well, battery was replaced last year and system looked over.

Wondering if it's transmission related myself, seeing as how on hybrid mode there is a separate pump providing pressure. Wondering if when the engine comes on line, and the trans switches modes something is happening there?

Re: 08 TAHOE Clunk when hybrid switches to engine
 

Have engine mounts and transmission mounts looked at for wear/loose.

Re: 08 TAHOE Clunk when hybrid switches to engine
 

I second this. The engine mounts are a pain but its cheaper to do them yourself than to have the dealer do it. You will need a ratchet angle extension for this.

Re: 08 TAHOE Clunk when hybrid switches to engine
 

Left motor mount, had mine replaced @ 107K, Chevy dealer mechanic said on Tahoes they all pretty much go bad by 100K , especially on PPV's and Hybrids, the extra hot weather in Phoenix speeds the wear process up as the motor mounts are made of rubber and steel. The clunking is the tell tale symptom. FYI, I paid $130.31 for the mount and $373.59 for labor at the dealer, I watched the repair(can see the repair bay from the waiting area) and it did take like 4-5 hours. The mechanic did warn me this is the easy side, the other side has all the hybrid stuff in the way.

Re: 08 TAHOE Clunk when hybrid switches to engine
 

I know its been a while, but my clunk/jerk problem tracked down to the aux trans pump and control module. there is a service bulletin on it, requiring and update to both parts to 2010 and new parts. Before spending the money, (new module needs to be programmed by dealer) I tried disconnecting all wiring connectors to module and pump. Fixed it for 20k miles or so. It started doing it again a few months back, reseated the connectors to the module (to right of 12 volt battery and under another control box), and problem is fixed again. Figuring its an issue with one of the connector plugs (which are different on the updated 2010 and newer units). Happens again and I may just remove plugs and direct wire. (new 2010 parts need to have plugs changed anyway)

Re: 08 TAHOE Clunk when hybrid switches to engine
 

Are you in a flat area?

Re: 08 TAHOE Clunk when hybrid switches to engine
 

Where exactly are these connectors located and how do you get to them?