We have had our Hybrid 1.5 years with no issues at 142,000 miles. It recently began to lurch when in autostop and starting out from a stop. If you accelerate slowly it switches to gas unnoticably. However if you give it moderate throttle it will begin to move normally then lurch very hard when the engine starts, kind of like the transmission was dumped into gear from neutral. Trans was serviced 20 k miles ago and was clean as a pin. Trans fluid is normal and the aux pump is not leaking. No codes either, any thoughts? Going into autostop just like normal and averaging 19.9 mpg, same as normal. Fresh plugs and wires along as all new fluids when purchased. Any thoughts?

 

lt1gmc, Thanks to the help of forum member Hillbilly_Hybrid who is helping me with what I'm also describing as a lurching problem, I'd recommend as a starting point that you may want to inspect your Hybrid Battery air vents for debris such as hair/lint etc. as a blocked battery vent could cause the battery to become hot which may cause Hybrid running issues such as lurching, hesitation, etc.. The vent is located just under the second row seat 'drivers side' closes to the door. To gain access, unfold the rear seat and let the seat fold/roll fully forward, then simply lift up only about half of the left side plastic cover which has about 2 or 3 easy to slide up/out clips holding the cover down.
I started lifting by hand right next to the seat latch catch "hook" mounted to the floor and the cover pretty much popped up then I supported the cover in order to clean the vents using a vacuum. Also the vents are used for the internal fan within the battery box. When you turn the key to the on position, the fan should turn on after a bit of time it seemed but my battery was hot when I went listening for it as test mentioned by Hillbilly_Hybrid in my similar topic. I'm not 100% sure if the fan runs when cold though as I didn't give it much thought until now.

If the image works below, here is 8 years of buildup which really isn't to bad being that my wife who drives it 90% of the time is a professional dog groomer.

 

Thanks for the tip. My vents are clear and the "lurching" can happen even when just starting out while everything is still somewhat cool. Hopefully HH will chime in, I know he had a tremendous amount of experience and knowledge with the Hybrids. Before the bankruptcy we had Hybrid engineers in our Delphi plant who I would be able to ask.

 

Hey guys, I'm in my driveway with a 2008 Yukon and my Tech 2. Here are some things any GM Tech can do with a Tech 2.


1) After selecting the 6.0L V8 LFA engine option i nthe Tech 2 menu select F1: Battery Energy Control Module


2) another F1: BECM Data Display continue to next set of choices in the BECM Data Display options


F2: will allow the service guy to see ALL 5 temperatures.


Inlet air, Outlet air, Temp Module #1, Temp Module #2, #3 and #4.


F3: is also what you guys need to get a look at.


F3: Voltage Data there are 20 volt meter readings and below #20 is a Min and Max reading.


The difference in min to max is what you guys need to get a look at.

 

Part 2. From the Voltage Data display I did a Quick Snapshot of a hard set parking brake while Brake Torquing it to get voltage difference and amps.


At a 15 amp draw I had 15.5 Max module voltage and 15.4 Min module voltage.


So again is it a battery problem?
If too hot, is the fan working? The Tech 2 can turn the fan up using the BECM Special Function.


It can command 60% or 2800 rpm. You can hear that.

 

Didn't believe it was a battery problem as it runs on electric all the time and can go a couple miles on electric. Problem got really bad in the last couple of weeks, so I did some research: I found a tech bulletin about the auxiliary trans pump and or aux trans control module which described my issue perfectly. Problem is you have to use 2010 parts to replace either which require splicing the wiring harness as the new plugs/connectors are different. Also the module has to be programmed, removing this as a do it yourself fix. I decided to use my electrical trouble shooting experience and unplugged all the connectors and re-seated them. So far and 700 miles later no problems.

 

lt1gmc, did unplugging the aux trans pump module resolve your issues? I've been having the same problems & 3 trips to the dealership later, the last one WITH the service bulletin addressing my driveability concerns, I still left without resolution. I know this is an old post but any information would be helpful. Thanks!

 

Yes, unplugging the large plug with the big size wires, then replugging has taken care of my issue a couple of times. I usually get 6-12 months before it re-occurs. I figure next time I may just wire around the plug.

 

Thanks for the updated info. I'll try that and see what happens. Do you think that the issue is with the wiring harness then? I'm about at my wits end and cannot drive the truck like this any longer. I'm just going to start replacing parts.. my husband says to start with the aux trans pump module but I'm not sure..

 

I believe the problem is in the connector body. There is a short wiring harness out of the Module with a plug that plugs into the harness I believe is going to the trans aux pump. That is where I think the problem is in my case, and the reason I believe that is they reconfigured the plug and harness on the 2010 and later models. The old aux pump or trans modules are not available and if you replace either one you have to by the matching 2010 module or pump because the siring harness is different. Makes replacing them an expensive project, so whats to loose my unplugging and replugging the harness and conectors? Fixes it for a good while in my case. Good luck. That plug is easy to locate, its down under the aux module which is on the drivers side, below and to the right of the battery, just behind the left end of the radiator. (Right and left being from the drivers viewpoint.