I have a 2008 Tahoe Hybrid and am seeking feedback related to a hybrid batttery issue. The truck has 105000(not a typo) miles. We took the truck to the dealer after the transmission started shifting hard and hesitating during the summer. Only happens when the outside temp goes above 85 degrees F. Dealers answer was to drive it at highway speed for an hour to recharge the hybrid battery. This works for a few days. It appears that the type of driving my wife does(real estate agent), low speed in electric whenever she can doesn't make for a happy battery. I can't get any technical explanation from the dealer so we have moved onto an independent hybrid mechanic, which we will visit for the first time in a couple of days. Anyone else experiencing this problem?

 

is it the hybrid battery at fault or the 12v battery instead. the hybrid is good to last up to 300,000+ miles. the dealer can actually charge it without driving it in the highway.

 

The most likely issue here is HV battery temperature. The more you use the battery the warmer it will operate. The battery will not discharge below a pre determined threshold so the highway is not charging it is most likely cooling. Above and below specific temperatures the hybrid will limit battery usage and this can affect vehicle performance.

First check for HV cooling obstructions like floor mats blankets or "fuzz bunnies" in the HV battery cooling air intake. It is on driver's side under the big plastic carpeted cover. If no obstructions on the expanded metal intake continue to below.

When this happens again try the following for 15 to 25 minutes.

All windows and or sun roof closed. HVAC on high blower front and rear. Vent/Duct setting to floor. Set temperature to 60F. Max Cold NO recirc.

Drive above 45 mph for about 15 minutes. Why?

HV battery cooling air comes from the long slots in the HV battery cover just above the floor under second row seat. HVAC set to floor will cause a pool of colder air to form on the floor just in front of these inlet slots. You can feel it with your hand in a few minutes after these settings.

Inlets must be unobstructed!

The floor setting also pulls in outside air. Recirc is colder but the outside air actually pressurizes the cabin increasing cooling flow through the HV battery.

Higher vehicle speeds with outside HVAC air creates an even higher positive cabin pressure.

So steady state highway speed for 15 t o25 minutes will raise the charge but the temperature is a greater effect.

 

^thanks GM hybrid guru

 

Good information from Hillbilly. I have a newly-acquired 2008 GMC Yukon like the Tahoe at the beginning of this thread, and am trying to learn as much as I can about the GM hybrid system. It's 100+ degrees in Texas at the moment, and I've already noticed my Yukon runs in battery mode much more when it's cool (in the morning) and relatively little with higher ambients. I'm an electrical engineer with some experience in power conversion, and am wondering if there are some minor 'tweaks' that can be made to help optimize the system for very hot weather. How about installing a simple fan/blower in the air inlet (slot area that Hillbilly drew my attention to) to increase air flow? How could that not help??
Thanks

 

I think it has a built in fan already.

 

Thanks! But I'd like to confirm, and even if so maybe the fan is undersized for 100+ degree (outdoor condition) ambients. I need to find some information on removing (safely) that HV battery cover and understanding the current design. I would believe all this is already well-explored and documented somewhere (maybe even on on this site), but I haven't found it yet. Also, the temp sensor/location for the battery pack circuit is a mystery to me so far. I'd like to install a simple remote temp sensor and gauge and see what's the temp's like in there over varying conditions...!
Hillbilly -- insights??

 

TAustin: If you were good at fabrication and don't mind giving up some seat room you could build a "super charger" to try and force more air into the battery inlet and through it. It would be big, noisy, and probaqbly need 20 amps of 12V to do the job.

The actual cooling air inlet is an expanded metal looking screen (about 1.5" by 7") on the driver's side, under the carpeted plastic cover ,under the middle row seat. Careful the trim clips are easy to break.

As electrical engineers are taught power = I^2*R. The battery has resistance and heats up when we use it or charge it. This particular battery has its own controller that among other things controls the cooling fan speed. It has multiple sensors to measure several actual cell temperatures and the cooling air.

I do NOT recomend opening it up!

If you want to you could put a sensor or thermocouple at the expanded metal air inlet, keep it clean, and then make adjustments to your air conditioning to provide the coolest air to it.

 

The easiest thing you can do is park in the shade, keep windows cracked and put heat shades/reflectors up against the windshield. Anything to keep the cabin temp down. Once the battery cells heat up, it takes a while to cool them down, even with max A/C and vents directed toward the floor. Might even consider one of those solar power vent fans you put in your window. The Prius has that roof solar panel/cabin vent option for just this reason, even though it's overpriced and gimmicky compared to much cheaper options. If you have a black vehicle in Texas and the car is going to sit at work all day, a breathable car cover would probably be a good investment. You'll get full EV capability back much quicker after starting.