GM's new charging "logic"

[ToddCarey]

I have a new 2007 GMC Sierra 5.3L. Nice truck, I really love the package GM has put together. I had an experience that I wanted to share with anyone who may have a 2007 Silverado (new body style), or the new Sierra.

GM has substantially changed the logic used for the charging system. In the "old" days, when the car was running, the charge system targeted a certain voltage (usually 14.1) and ran the car at that voltage when it was running. Sometimes, during periods of high load, and usually when at idle, the voltage may drop down, but would pick back up once you started to move again.

Well, that is all changed with the new charging system of the Sierra/Silverado. Now, GM has an Electrical Power Management (EPM) system which is designed to monitor and control the charging system and send diagnostic messages (this, and the following, is wording out of the GM service papers). The EPM system primarily utilizes existing on-board comuter capability to maximize the effectiveness of the generator, to manage the load, imporve battery state-of-charge and life, and minimize the system's impact on fuel economy. The EPM system performs 3 functions:

- It monitors the battery voltage and estimates the battery condition.
- It takes corrective actions by boosting idle speeds, and adjusting the regulated voltage.
- It performs diagnostics and driver notification.

During use, there are 6 modes of operation and they include.

- Battery Sulfation Mode
- Charge Mode
- Fuel Economy Mode
- Headlamp mode
- Start Up mode
- Voltage reduction mode.

There is a lot more neat information I was given by a GM technician from a service call I had on my Sierra. After I got the truck, I would note that sometimes when driving, even at highway speed, the voltage would drop back to around 12.5 volts. Being from "old school", my immediate thought was that the vehicles computer was having some problems. My other vehicle is a 2007 Corvette, which is ALWAYS at 14.1 volts, no matter what speed or other circumstance. I mistakenly thought that if GM had come up with some new logic for controlling the new cars, they certainly would have done the same thing to the Corvette as it is kind of the "crown jewel" of the Chevrolet line.

Well, I was wrong. After some fussing at the dealer service rep, he assigned my car to their top service technician. He printed out a copy of the GM service bulletin on the charging system. The "new" logic they use is really amazing and designed to not only relieve the load on the engine (fuel economy mode), but to increase the battery life by not overcharging.

If you read the owners manual real closely, it does address these new modes of charging, but in my opinion, not very well. I just wanted to pass on some information that may be helpful to someone else who us used to the old charging so they do not stress out with the new GM trucks.

Todd Carey

[jeremy96gase]

Todd, Thank you for the information!

How are you liking the rest of the truck? Did you get the Basic or Premium interior?

[ToddCarey]

Jeremy - I have the SLT package, which is a GREAT combination of comfort and good looks. Overall, I have been very pleased with the truck.

I have purchased the K&N series 77 filter kit for the truck. It was an easy install and has given me around 1.5 addition MPG on the highway (from around 18.6 to about 21.5). I also have a Peragon Bed Cover. It is an excellant cover, easy to install and use. The "interesting" part is that it DID NOT give me any better gas mileage. I was expecting to see maybe an extra MPG due to a better airflow, but in several 1500 miles trips before cover to the exact same trips after cover, no noticable difference (I put the cover on the truck in March and the air filter kit in June). Go Figure....

Todd

[jeremy96gase]

Now-a-days they design these trucks so the bed has no aerodynamic drag. At least there is no air coming over the cab, and being sucked down so much it runs in to the tailgate. That was the problem with older trucks.

It's awesome you're enjoying you're truck :D