Whatever you want to call it, I've been through every possible post in this forum, and this has come up several times, and I've discussed it as well.

I'm a 2008 Yukon Hybrid owner, and it's now two issues, which I have to believe are related.

First: Coming to a stop, the car lurches forward when switching to battery mode. The possibilities I've seen in this forum could be related to the wiring harness, the auxiliary transmission pump and the #1 cylinder misfire (engine replacement solution). I've about ruled out the last one.

Second: When starting from a stop, nothing happens for a second or two, and then the car starts "chugging" between engine and hybrid mode.....it IS moving forward, but chugs. I have to stop and then very slowly start going again. This is a much rarer occurrence than the first problem.

Now, of course this is intermittent for me and never happens at the dealership. A couple of years ago, the check engine light came on, and the fix was to clear the codes and if it never came on again, it wasn't a problem. If it did, they were going to replace the aux pump. The light's never come on again.

All software updates have been performed as well. I've also pointed out this forum's suggested possibilities to the dealerships.

The big issue is that neither one of these problems sets off any codes for the tech to look at anymoe, but the problem is obviously still there. Since the dealership cannot recreate the problem, they can't/won't do anything about it.

It's to the point where I'm going to have to sell the car before this results in an accident on the road. If it gets to that point, I'm going to be inclined to buy a more reliable vehicle, or at least one that can be fixed. No sense in sticking with a car that can't be fixed.

Is there any other avenue I can try that you can think of? How do you convince someone there's something wrong with your car when they can never recreate the problem and the computers cannot sense it either?

Any help would be huge!

 

you are trying to confuse the computer! gas or EV. if you drive slowly, it will keep it in EV until 20mph. anytime to press harder or faster it will immediately transfer to ICE. I have no problem with the transfer and considered it normal. if there are no codes, then it is normal occurrence.

 

Jeff: this could be clutch slip. A bump or jolt that you feel but just not long enough in duration for the computer to set a code. During this rare chugging and barely going event you describe are you holding the gas pedal steady? Gas pedal changes are percieved by the hybrid system as torque requests.


You said. " When starting from a stop, nothing happens for a second or two". Does this mean you are not moving or it hasn't acted up yet?

Abrupt pedal motions will "confuse" the system. However steady pedal will still have these interruptions if a clutch slips.

Reasons for clutch slips are twofold in early 2008. The auxillary pump you told of and a clutch retaining snap ring that popped out of its groove in early models.

The 12V pump and engine driven main pump can and do get into fights. The engine always wins. There is a coordinated hand off between these pumps. If it is confusion try to tame the pedal motions.

If the snap ring has popped out... a hard acceleration forward starting with the engine ON will usually reveal it. In the engine on case the main pump dominates and can supply much more fluid than the clutch needs. If you "gas it" hard from a stop up to 20 mph and it chugs or bumps roughly, (as it starts to move or just sits there) it is most likely snap ring.

If you are toggling between engine on and electric back and forth, and it acts up, this is most likely aux to main and main to aux pump hand off loss of pressure. "Pump stall"

 

Hillbilly, that's an interesting take on the situation that I hadn't heard before, as far as the snap ring is concerned. If it comes up again, I'll ask the technician about it. For now, even though they had the car for over a week, they could never recreate the problem, but went ahead and replaced the aux transmission pump. They're reasoning was that they've had to replace it on their shuttle "bus" before and it's only a $200 part. At least they're trying solutions instead of sitting on their hands like the other dealership.

But on to your questions. As for holding the gas pedal steady, I do that until the problem starts. When I'm attempting to go forward at a stop sign/light, and the car starts lunging/stopping/lunging/stopping over and over while pushing me into the intersection, I put on the brake to stop that nonsense, so I might be able to operate normally once it stops.

"nothing happens" - this means I press on the gas pedal (not hard) and nothing happens. No forward movement, no engine coming on (I can't be sure if I'm in battery or engine mode.....it's only happened 3 times in 3 years and only once when I was driving), nothing, and then I lunge forward, stop, lunge forward, stop. It's hard to find the right words. Start, stop, start, stop?

Hopefully these things won't happen again, but I will try my best to remember more details next time.

 

Well, that apparently was not the fix I was hoping it would be. My wife just reported that it's happening again, both when braking and when starting from a stop, and she's not flooring the gas pedal.

At least the check engine light came on this time, so the computers will have something stored in them. Unfortunatley for her, she's ready to be done with the Hybrid experiment altogether, and I can't exactly blame her the longer this drags on.

Will post with what they find out this time. She's taking it in this afternoon.

 

Sorry to hear that and I don't blame your wife. Make the dealer get the codes. Write them down. Check for codes in history too. Don't let them clear anything until the next step! And not just the engine. The hybrid controller is now the master of the vehicle. The engine is just a torque source.

Ask them to get the "freeze frame" data. If it set the light it also stored a bunch of pre-programmed data too. That can be saved and emailed to GM.

I wish more dealers would make use of the tools available. All we used to have was eyes, ears, volt meter, and a test light. Too many just clear the codes first and hope the problem goes away.

Now another question. you said. " then I lunge forward, stop, lunge forward, stop. It's hard to find the right words. Start, stop, start, stop"

Did the tachometer indicate that the engine had come to life or was it just getting going?

When they did the pump, did they do the controller too?

After the light came on, did it ever go back to electric again before the next key cycle?

Hopefully codes and data will settle this once and for all.

 

Sorry it's been a while since my last post, but the hybrid appears to be working properly again......until next time?

In any case, no they didn't replace the controller that time, but that sure was what the codes indicated this time. Having successfully replaced the controller, the car no longer has the issues.

Hopefully things will be better now. Still wanting to reroute the exhaust and put the spare in, as I have most of the parts from a junk yard, but I may bite the bullet and wait for the 70K warranty to expire, unless I want to pay an arm and a leg and let the dealership do it......I THINK that would keep my warranty intact, since GM came up with the replacement kit to do that. That's still a little murky to me.

 

If you have the issues again, question the dealership about the spring replacement in the pressure regulating valve.

As far as the exhaust, do it. As long as you are not doing anything with the sensors or emissions equipment, there is no issue with warranty. It doesn't change how the car runs in any way.

 

I'll keep that in mind, should anything else happen with regard to the main thread of the post.

As for the exhaust, in different threads I've gotten the vibe that the dealership is told to look for any modifications, which would nullify the warranty. But, I haven't verified that with GM by any means.

 

They don't just void your entire warranty.... If you have an intake, and your mass airflow sensor fails, they may not replace that under warranty. If you have wheels on the car and the DVD player stops working.... their is no correlation between the two and you are covered. It may be a process, but if your dealer is not cooperating, you can fight them and make it up to them to prove the aftermarket parts caused the failure.