sounds like you have this query covered....I would have to dig around to come up with that info. My Dlr forgot to order the gasket set so I was down a couple of days. Also they diagnosed it in the shop after a bit of testing. My issue was very intermittent (happened twice only) and those are sometimes hard to sort out without good techs.

 

Ok, this is my take:
Happened to me today, but I've seen signs of it before (and reported in threads).
Today was 103 degrees and no clouds. I did a bunch of short errands in the peak of the heat (1 to 5 pm).
I used autostart sometimes to cool the car for a minute or two before driving. Usually, the car will autostop before leaving a parking lot when I do this. Today, it was in V8 mode at stop signs and traffic lights and did not want to autostop much. Sometimes it would, and sometimes it wouldn't. Also, sometimes it would not even go to V4 and not even go to 99mpg.
Conclusion, it was trying to charge the battery pack. The battery pack that probably was exposed to 160 degrees or so of ambient temp plus its working temp. So it could not dissipate. Now, I've driven in these temps before. Once when it was brand new, so that was not an issue. Other times I probably had the rear A/C on for the kids. I usually don't do running around town without the family. On hot days and alone, I would be driving on the highway to work.
So, after abusing it for the day, on the way home the behavior kept getting worse. Finally, the Tahoe seemed to expect the motor to assist me from stops as I gently accelerated near my home, but there was no energy in the batteries. It went nowhere for about 1/2 second, then jumped forward on V8 power. Totally different gear/driveline behavior than I've ever experienced, but it made perfect sense.
I imagine if I put my foot in it from the light, it would have went to all-engine much faster, but it just expected to have some electric-assist that wasn't there.
So, Guss, Mike, others, heat and battery capacity seem to be a major factor here, and we know that heat and battery capacity are inversely related, which makes this problem non-linear.

 

FJ,
Thanks for your feedback,this is our daily city driving conditions (high temperatures 95+F, short trips, hilly roads, somtimes use remote start,AC on front and rear all the time)
The past few days temperatures have cooled down relativly speaking from 95-110 F to 80-95F. when I turn off the AC, My Tahoe performs so much better. It goes to autostop much faster and stays for much longer periods of time even on a slight uphill it stays in autostop.
Yes, the AC does drain the battery in my Tahoe for sure, I have posted about this issue earlier.
Based on my road conditions,short trips and high sumemr temperatures (95-110F) there is no way to get above 15-16 MPG with both Front and Rear Ac on.
The battery cannot keep up with AC and driving on EC mode for sure. once the AC is turned off, and I open the windows, My Tahoe acts so much better.
In Winter with Auto start, heater, and the fuel quality and performance also affects my mileage.
So what I concluded the ideal conditions for best perfomrance in my Tahoe would be with AC OFF, outside temperatures 65-82 F, flat roads,and light foot driving, then I might be able to get 20+ MPG in city dirving.
anythign other than the above conditions, the fuel effeciency drops below 17 MPG

Thanks again FJ

 

Guss,
I'm not so sure it is the A/C. Yesterday I had the rear A/C off. I think it was heat-soak of the battery packs that really hit it the most.
Now, capacity of the pack does not decrease much with temp, but chance of cell-damage goes up dramatically above 100F, and at 120F becomes 80%. So, there is probably a battery management IC on the pack that controls the charging of the pack independent of all other systems, and just looks at the pack temp, voltage and rate of charge/discharge. So, if this IC were preventing the pack from delivering energy, the hybrid controller could be trying to charge it and trying to take energy from it, but it would be denied for safety of the batteries. Thus, this would cause the lower fuel mileage, as the charging would be wasted and the "jolting", as the hybrid controller, seeing voltage on the pack, would be expecting it to be able to deliver current to the traction motors, which the IC would be blocking.
It could also be as simple as the temperature protection fuse has opened on the pack and taken it out of the circuit for a few seconds to a few minutes. I'm not sure how long this would have to be open for this to set a trouble code. Seeing as they tested this in Death Valley, I would think they covered this ground. But, then again, since they had to ride inside these things, they may never have let the battery packs heat soak.
This is my working theory on this issue.

 

FJ and Guss: it's all about power and temperature. The vehicle requires power from the battery for propulsion (electric), starting the engine (with the transmission), uninterrupted accelerating while starting the engine, and accessory loads (AC 12V power).

There are limits on HV battery power that are highly temperature dependant. Too cold and power is limited. Too hot and the same.

Air conditioning has three parts in power loading. The HV compressor, cabin blowers, and main engine fans. Air conditioning can use upwards of 6-to-7 killowatts for all HV and 12V loads.

So you are driving in electric with full AC front and back. The battery may be on the hot side and into the limiting zone. The limiting zones are in place to protect the battery. Therefore your experience with electric driving will varry with AC load and limits. The vehicle will come out of electric real easy with a hotter battery. Where on other days with a cooler battery (~30C) and very light vehicle electrical loads you can hit 30 km/h easy. Even hotter yet and NO Auto-Stop.

Anyone that drove the old Quadrajet (quadra-bog) carburetors will remember the sag when kicking in the gas pedal fast with a non adjusted one.

Electric driving needs power let's say about 12 kW for 12 mph. Starting the engine needs power reserved. (4 to 8 kW) I don't know exactly. The AC and all those blowers and fans are using another 6 kW.

NOTE: important point here.

To avoid the (quadra-bog) even more power is needed while the hybrid is getting the IC engine up to running speed. (lots of power here) IC engines can't make torque at zero speed like motors. And this extra power is even greater at higher electric driving speeds.

Sorry Jet but this extra power to avoid the BOG is why no electric boogie above 30 mph. It would take much much more battery to go faster without the old Qudra Jet bog feeling. I for one would like the option of buying more battery.

(12 kW + AC + Engine start + Extra to avoid bog ) is not supposed to exceede the limits based HV battery temperatures at that time.

The hybrid does the math and knows how much electrical power is needed based on your actual vehicle speed when you kick that pedal a little more to start the engine.

When limits are in place, it will kick out of electric real easy.

I have figured out how to force cool a HV battery if you care to try.

1) All windows up to help pressurize the cabin in later steps.
2) Put front and back HVAC on floor as if heating feet in winter.
3) Make sure no obstructions from the floor ducts under the front seats to front of air inlets on HV battery cover.
4) Run high blowers at 60 F coldest Air Conditioning setting
5) Vehicle speed increases cabin pressure as the cabin fresh air comes in from the base of the windshield. When I slam the door the accumulated pine needles up there jump. Keep this area clear.

Re-circ will be colder air but it won't pressurize the cabin, it won't create a cold pool of air just in front of the HV battery inlets, and it won't supercharge the HV battery flow.

I have been able to take a battery from a termperature that would not even alow Auto-Stop down to allow Auto-Stop in 10 minutes. If you listen for the battery fan and then do this even better.

In a few minutes you can feel the cold pool of air on the floor just in front of the HV battery inlets.

 

Hillbilly,

Thanks for your feed back and the tip to cool down the HV battery, much appreciated.
FJ,

This explains the fuel effeciency in low and high temperatures.

I just remebered also in winter, The vehicle needs time to warm the engine oil and HV battery before it goes to Autostop or V4 mode, which doesn't help the mileage specially in short distances.

so extreme high /low temp affects the Hybrids fuel effeciency for sure.

Thanks all for your feedback

 

Well I just got back from Myrtle Beach SC. The jolt happened again there. The outside temperature was about 92 degrees with about 50 to 60 percent humidity, it was about 8:30 PM. The Tahoe was sitting in the parking lot for about 2 hours before we got in to leave. We only drove it about 5 miles total that day prior to it setting for those 2 hours. I went to pull out in traffic and it didn't want to move at all in electric mode, I had to put it to the floor to get it to move so that I wouldn't be in an accident. Usually when you put it to the floor, at about 3500 to 4000 rpm you feel a harder pull in these vehicles like you have a 50 or 75 shot of nitrous. I did not feel that this time. It felt like a standard 6.0 pulling a 6500 lbs vehicle through the revs. After about 20 minutes of driving or so, I put it to the floor again and this time it reacted like it should. Now this vehicle doesn't do this when it is hot all the time, it is very intermittent. To me I can see if there is a loose connection to the transmission which may not be sending the correct signal to the system for electric assist. My vehicle was manufactured on 10/07. This puts me in the possible predicament that Jet and robmck had with the bad crimp in the wire harness. It has to go back to the dealer anyway for tire hum as the tires aren't wearing correctly creating high spots on the inner tread, there is a TSB on it, but I can't see the full TSB. Can anyone look at the full TSB's for these vehicles?

 

Hi All,

I'm still experiencing the same problems noted above by myself and other owners, where on hot days and after the car has been sitting for a bit after some light city driving, the truck hesitates and does not accelerate as it should. When this problem is occurring, I also notice that the RPM's tend to flare. This is very intermittent and I can never get it to reproduce when I want it to. Although, I was able to get one of the techs at the dealer to witness the flare as if the transmission is slipping a bit at 2nd gear, but not the hesitation.

I just recently got it out of the shop where they had it for about 5 days. They had GM engineers walk them through a reprogram process that was listed under one of the TSB's for Hybrid Driveability concerns/problems which includes symptoms of flare, slip, stall reduced EV range and a host of others. I will try to copy the TSB and post later.

Anyway, the fix didn't work. The same problems reappeared a day later. According to the TSB, this process should be done twice at most if the first time doesn't fix it. If it is performed a second time without resolution it says they should look into clutch slip. I don't think this is related to the transmission harness as posted elsewhere, because I have had the harness replaced, as well as the auxillary transmission pump. There is another TSB regarding loose wiring at the transmission associated with some other problems such as IPC fluctuation (which I am having and the truck is back in the shop for a fuel gauge that fluctuates when in park), door lock cycling (I don't have this), transmission shifts hard or doesn't shift. I asked the dealer to look into this. They said they would, but they don't seem to think they are related.

I am with those that think this is a Hybrid Battery and heat problem, although I haven't seen many owners of the newer Hybrid's complaining of this problem. I only seem to experience this problem at extreme temps but as I live in AZ that is about 4 months of the year. The reason I think this is because prior to the start of this summer, it ran fine all fall, winter and spring. They had replaced the tranny harness at the end of last summer and the problems seem to go away so I thought it was fixed. Of course when this summer rolled around it was back to the same old tricks. Mine is a 2008 built in 2/08. I've only owned it for 14 months though as it sat on the lot at the dealership for a while. I bought it new with only a couple hundred miles on it. I do have 22" rims on mine, but they were installed by the dealer before I took possession. I also have DVD headrests installed, but they were installed after I started experiencing these problems, so I know the two aren't related. I've recently submitted a complaint/claim to GM and the BBB just so that this goes on record. I heard from GM this morning and they are going to be researching it and contacting me next week with some sort of solution or resolution. They seem very nice so far and sound as if they want to do anything possible to provide the best customer response.

That's all and probably enough for now! I'll keep you all posted in case my issues can help others. If anyone else has any thoughts or ideas, please let me know.

Patrick

 

If you read one of my very first posts, it describes the trip home to SoCal from Las Vegas after purchasing my Tahoe in Phoenix in the Summer of '08. 115 degrees outside in hours of bumper-to-bumper up a mountain out of Vegas. The Tahoe was flawless, but was heavily air conditioned before hitting the traffic.
My point is that at 3,000' up the mountain I hit a Prius graveyard. Bunches of them with the hoods up and owners on cell phones. I'm sure they had battery issues and the engine probably was not meant to pull the car without battery assist up that grade in that heat, and to top it off, seeing this behavior, those Priori were probably trying to charge a battery pack that was not accepting a charge or had already been damaged. This probably exasperated the problem further. I'll never forget that sight, not a Prius to be seen on the road for hours after that...

 

I was in vegas last summer and on the drive back saw traffic for two hours where heat was like fjungman 115F and the escalade hybrid temp would go up to 225F on auto stop and when the ICE kicks in, lower the temp to 205F. This is with both front and rear A/C on fullblast. never had any problems. I was worried to call a tow truck just in case but never happened.