Yesterday, I had been driving in traffic on urban blvd.'s for awhile. The engine was warm and the batteries should have been in a reasonable state of charge. I had stopped to gas up (my best mpg yet, 19.9 calculated) and was shut down for around 10 minutes to do that and it was around 42F outside. I pulled back out onto the divided roadway to bumper to bumper traffic. I noticed that the ICE did not shut down much, meaning it was running most of the time with only a few shutdowns in about 8-10 minutes of driving in this stop/go traffic. I drove at what would have been autostop mode any other time. The vehicle runs in stop/go traffic really well in autostop with the ICE coming on only occasionally and then going back to autostop. But this time, ICE was on most of the time. It seemed to be idling rough too and at around 1500 to 2000 rpm, like the fast idle was on. I punched the accelerator a couple of times to try to reset it...knowing that being fuel injected and already warm, that could not be the issue. After the 1.5 mile/10 minute crawl with a barely noticeable roughness to the almost continuously running ICE, I cycled the DIC to notice that the AVG MPG had gone down to 15.7 mpg...it almost always shows in the 19 mpg range +/-. Then, I pulling into a parking lot. When parking, I pulled into, then backed up to straighten out, then pulled into the parking space. When I shifted from reverse to drive (while stopped), it was as though I had done it while moving and the gears jumped! It made a definite clank when I put it in drive and it jumped a bit.

I don't know what all of that was but I immediately called the dealer and set up to take it in this morning. They have had it all morning and haven't talked to them. Just giving them time to run the codes and look at it. This was on the '09 Two-Mode Hybrid Silverado. What do all of you think?

 

I've had a couple of occasions, before the update, that the ICE ran when I knew it shouldn't be. I did not notice the higher RPM, but it did not shut off, even crawling through a parking lot at the end of my drive. I attributed this to some "mysterious" software feature that is extending battery life. What I mean is that the battery is managed and needs more than just straight charging and discharging with use. So, I am guessing that there are times when it runs it down lower than normal and charges it all the way up, to prevent battery damage.
Now, understand this is just a guess and boarders on a rationalization of this behavior. I will be interested to find out what the dealer has to say.
My problem only happened two or three times and cleared after about 15 minutes.

 

Auto Stop is a function of many factors. Engine coolant temp, trans oil temp, and battery temp are all factored in. As the outside temp gets colder it will take longer to get your first Auto Stop of the day. I drove 22 miles before my first A-Stop today. 13F with 12 hour soak outside. Why? You need a hotter engine block for comfortable cabin heat in A-Stop. For outside temperatures below 50F look at the following. Engine coolant needle is straight up or around 200F, and the DIC tells you that you have 100F transmission. And you have had the cabin heat on long enough to get the battery up to about 72F, you should be in the zone. Park time outside needed to cool the trans and battery to ambient is 12 to 18 hours. Lots of mass to cool means slow to heat also.

A little trick for battery thermal management.

To use your HVAC to warm up or cool off the pack, set the manual HVAC to floor, outside air, and full blast fan. Recirculation actually seals off the cabin and reduces the flow from the cabin to the exterior vent. Sucking in outside air, thermally conditioning it, and directing it to the forward facing floor cooling inlets allows a slight super-charge so even if the battery fan is not running, you can have an effect on battery temp.

Driving with windows down can create a negative cabin pressure and impede flow.

This said I hope there is nothing wrong with Mel's truck.

 

I have noticed mine runs a little rough sometimes but it has been in the zero to teen range temp wise and I wasn't really concerned about it. It feels like its loading up as in rich but it seems to clear. My ICE does run a bit longer in the winter than it does in the summer when started up cold.

 

I remembered another fun fact on the cold now that it is here. When the battery is cold the impedance has a significant change. Therefore voltage control of the permanent magnet motors gets tricky to stay withing voltage limits. Engine combustion is less stabile at very light loads. < 35 kPa MAP. So when the ICE is not allowed to do much charging, you may notice it. In the good old days we could brake torque against the converter to heat up the engine and trans. Now if you rev up the engine the motor/generator spins up and the EMF runs the DC bus voltage up.

If you commute every day like me the trans and battery don't have time to cool all the way down to outside temp. I had 13F this morning and DIC said 39F trans but it was a while for the A-Stop. In the Summer I get my first A-Stop within 2.5 miles.

 

Interesting on the Trans Temp > 100. I noticed my trans is not getting to 100 when I was not getting A-Stop. It was quite a bit of driving, so I was surprised is was so cool. This probably explains the lack of A-stop a lot better than my speculation.

 

As the ambient goes down the engine coolant and trans fluid thresholds go up. These 2 Modes have been to the Arctic Circle this time of year and even there eventually they will A-Stop.

 

I appreciate the thoughts on this. The dealer called and as expected, no codes, and the tech drove it quite a bit trying to simulate the conditions I descibed. As mentioned above, it was only 42F outside and the vehicle was already warm from a 30 mile drive, but the last 5-10 minutes before I fueled up was in stop/go traffic. Then after fueling, the above occurred, so it should not have really cooled down. I have noticed that it holds it's heat really well and even on a cold day, you can shut down and for 15 or 20 minutes, you still get back to 200 degree engine temp.

Gotta go pick it up. They documented it and I will keep an eye on it...and I am with Marty on this one...I hope there is nothing wrong with Mel's Truck!

 

A couple of other possible reasons for not much auto stop time:
*Engine is running once-per-trip diagnostics and may stay running just for that purpose.
*Your battery and trans should have been warmed up, but if you had any significant EV time prior to keying off, your state of charge may have been down, so the engine was on to bring it back up. You might see this if you were going through a sub in EV, keyed off, and then the next time you start back up, the battery is on the low side.

As for the clunk, it sounds like the forward-reverse action built up some lash in the trans. Normally the motors take up the lash, but perhaps after FWD-Rev-FWD cycling maybe the parking pawl was loaded up and it released in such a fashion that the motors couldn't compensate quickly enough. Another possibility is driveshaft wind-up.

Regarding your avg MPG, do you reset when you refuel? That's a big drop for AVG MPG in a short time, so it seems like your AVG was reset recently.

 

Yes, I reset my AVG MPG, Trip miles, and fuel used every fill up. Funny too, it resets to zero and then the AVG MPG immediately goes back to 20.0 mpg when I turn the key back on after fill up and adjusts from there. That is the EPA published estimate for the 4WD trucks, 20/20. It was back up to around 18 when I took it in this morning and then around 16.9 when I picked it up. I didn't note the mileage when I dropped it off so don't know how far they drove it, but was told he drove as if in stop and go traffic for quite awhile. However, the dealer is in the country and no divided roadways other than an interstate highway and small town streets. Life is good, they did my 3000 mile oil change and put in Mobil 1. I am running my tires at 40psi across the board and the last fill up was my highest mileage until this funky engine stuff after this fill up yesterday. So higher tire pressures increase mileage just like the Prius.