After returning from a trip to a dead battery in my 2006 C6 at the airport parking, I got AAA to inspect/replace the battery. They connected a device to the data port somewhere below the steering wheel to preserve information as they explained. After all was set and done, I left and got on the freeway on my way home and I started noticing that the car didn't had the typical power delivery. That was last Friday. Yesterday, I noticed that to make a normal pass on the freeway at a reasonable speed I needed to swicth to 5th gear to make it fast enough, which normally I don't have to do. This morning I was making another pass on a two lane road with about 4 or 5 cars behhind a truck starting to roll from a red light, which I had done many times before in third gear, and it took an eternity to get pass this group.

So my question is, have anyone experience a performance degradation after replacing a dead battery? I am suspecting that perhaps that device that AAA utilized to preserve information might have actually restored information incorrectly causing the car to perform poorly. Does this make any sense to anyone? Is there a way to restore the car to Factory settings? The car otherwise drives normally. It is only when I push it that I notice that the power is not all there anymore.

BTW, everything else seems normal with the car. This is my daily driver with about 110K mi. in 5 years of ownership and this dead battery been my first problem after warranty expired many years ago.

Thanks in advance for any help,

Arnaldo.

 

The only reason I can see is to connect a ground wire to the PCM in case of a voltage spike that could fry your car's PCM. I doubt they actually re-flashed anything. Have you checked with AAA?

You may want to check to see if there are any codes.

 

Thanks for your reply. I will check on the forum to see how the read the codes and into this PCM wire that you suggested. This car has been bulletproof since new so I have very little knowledge/experience on having to troubleshoot any issues with it.
Yes, contacting AAA was my first thought and the option is still on the table, but I want to educate myself with the experience of others in this forum before I explore that route. I am not hopeful that those guys at AAA will be much help, but I could be wrong.
Thanks!

 

One more thought. When the battery is disconnected or dead, the Long Term Fuel Trims are zero'd out. That mean, the PCM will need to re-learn the fueling curve at anything less than wide open throttle based on the O2 sensors output. So it could be running lean or rich under light to medium throttle situations. Under WOT, whatever the LTFT% error is, that will be used.

My recommendation is to drive the car normally and it may return to its old self.

 

Actually I would disconnect the battery occaisionally to have the PCM relearn on purpose, if the car just seemed lacluster from too much putting around town, just a guess. It would seem to store some less than ideal info, if that makes any sense. Did this with my LS2 GTO too.

Everytime I did this, once I drove it for maybe an hour, I would get a temporary small performance increase (a little better throttle response, etc,) for a period of time. Kind of like rebooting your PC. If you're really feeling a degredation of performance like you say, I'd be suspicious about what they connected to the OBDII port too.

 

I also wonder what they connected to the OBD11 port. The C6 only needs the windows re-indexed when the battery is replaced so most of us just do that. It takes on a few seconds. If someone wants to save settings most mechanics use a nine volt battery hooked to the cables while the replacement is done.

 

It is very interesting what you guys are discussing about the car relearning parameters and such. I drive a little over an hour every work day each way, and the car was not driven since I returned from the airport last Friday until yesterday. The drive home this afternoon was much better. Perhaps there is something to this as you guys are suggesting. I will wait till the end of the week before taking further action since perhaps (fingers crossed) this is the issue. Thanks so much for your help!

 

Yes, this is a good question and I should have been more inquisitive when this was done. Fortunately, I found the business card to the AAA service company and I placed a call to their offices to inquire about this device. They indicated that this device is called a "Kan Unit", which apparently its sole purpose is to apply and maintain power to the car while the battery is installed. They claim that the device does not actually retrieve/restore parameters or other information on the car.
I did a web search for this "Kan unit" and nothing comes up. So, I don't know if this is their name to the device, or a market name. Anyway, if what they said is correct, and as you guys earlier suggested, it might be a matter of waiting a few days for the car to relearn the necessary data to start behaving as before.

 

Interesting. Makes sense and I'm sure it's an easy way to maintain things. Good luck. If you don't think the power improves you could disconnect the battery for a few minuets and see if it improves.

 

The name is CAN not KAN. It makes sense they applied power to the PCM to keep all the setting there. Not sure why they go thru the OBDII port. I've seen power units that use the cigarette lighter outlet with a 9 volt battery.

I wouldn't recommend disconnecting the battery as you outlined.

The relearn process is continuous. It never stops learning.

It sound like to me, you are feeling the affects of increased IAT (Intake Air Temp). As the IAT increases, there is less O2 to burn so the engine makes less power. The stock timing advance is too aggressive as IAT increases, so there is a separate table that pulls out timing according to temp and manifold absolute pressure (MAP). Some guys reduce the amount of timing being pulled out and claim power increases. The GTOs were famous for this along with high IAT due to the routing of the coolant.

If you are that concerned, I would have it tuned.

 

Just a guess, but the OBDII port is always connected to the battery and has voltage. Some cars cigarette lighters are only "hot" (voltage wise) with the ignition in the on or accessory position. The OBDII port is a great way to apply voltage to keep a vehicles settings and the same unit can be used on many vehicles.

Bob

 

it's called a memory saver. check it out. there are different types available. one, as you described, goes through the obdII port. others hook up to the cigarette lighter with either a 9v battery, or an extention cord and power outlet. either way, the only purpose it serves is to save your vehicle's memory, radio stations, clock, check engine codes (if any).. things like that. it doesnt reset or relearn anything. i use this every day at my job, it's not going to hurt performance. you have another issue going on. unless, and this is totally possible, the memory saver wasn't hooked up right or wasn't charged fully. then it would cause the pcm to lose it's memory.

 

If you look in the GM service manual for the car, it does not say anything about hooking up any device to save any settings when performing a battery change; it is not necessary. You just disconnect the old battery, remove it, and install the new one. The only procedure that needs to be done after that is re-indexing the windows. I just changed the battery in my '08 coupe last week and followed the proceudre outlined above in the service manual and I lost no "settings". Didn't even lose my radio presets and the clock had the correct time. They should not have connected anything to your car to change the battery. Whatever they did hook into your OBD II port has no doubt caused your issue, IMO.

 

You don't know that. The only way any of the engine control setting could have changed is by re-flashing the PCM.

 

Yes, the memory on a lot of things is retained. However, the PCM learns its settings based on the operating conditions of a particular vehicle based on feedback from its sensors. Once the battery goes dead or is disconnected all of those learned parameters go back to a nominal setting and the car relearns the correct settings. That is one of the reasons why you have to drive around for a while and do several start sequences to pass an emissions test if the battery has been disconnected.

Resetting those parameters by disconnecting the battery cables will usually end up with poorer performance since the nominal settings don't take into account conditions that exist in that particular engine and its control system.

Bill

 

I wrote IMO (in my opinion) - didn't write that it was a fact. But I do not believe in coincidence; especially when everything is working fine until someone plugs something into the OBD II port. The OP can certainly draw his own conclusions.

 

Mine didn't have to relearn anything - or at least if it did it was so sublte as to be unnoticable. My car started immediately with the new battery and performed and drove just as it had prior to the battery change. There was no loss of power and I used no device, and I did nothing to save any "settings". Maybe the '08s are different, or maybe just mine is, but I tend to doubt it.

 

Just curious, what do you mean by "have it tuned"? Thanks

 

Find a Corvette Shop that can recalibrate the PCM/ECU for better performance. There are numerous shops that do this. The one that I use is Corvettes Of Westchester in Westchester NY. The owner Chuck, re-tuned my 06 MN6 Z51 Coupe after I installed headers, ported Throttle Body and a VARARAM.

Before the tune, the car ran really rich (due to adding the performance parts) and the fuel mileage took a dump. Before the modifications, I could get 25-26 MPG Highway. After the mods were installed and with out the tune, it dropped to 23 mpg

Chuck tuned it and there was a significant improvement in all areas!!When I drove from CT to Bowling Green KY and back, I saw 28-29 MPG with a fully loaded car and 2 people. There was a significant increase in throttle response and the performance significantly increased. Never had the car re-dynoed but, it had more power after the tune.

On a completely stock C5 or C6, tuning the car can remove the CAGS, give you better fuel mileage, and find some hidden HP. Give Chuck a call discuss your goals and see what he says. If you have a A6 Tranny, the car will feel like a new beast!!!!

Tuning is accomplished thru the cars OBDII port using tuning software. Chuck uses EFI Live. The software enables you to manipulate the ECU calibrations to achieve a custom tune better suited for your specific car. If you add performance parts, the tune allows you to readjust operating parameter to maintain the correct AFR , timing and transmission calibrations if you have an A6.

Bill

 

As the operating characteristics of the engine change over time the PCM learns reacts to those changes by changing what part of the tables it uses for certain air flow and load conditions. When you pull the battery these changes are erased. When you start the engine the PCM will relearn them over a short period of time. It has been that way since they started using computers to control engines. It works great and allows the computer to adjust to the engine as it ages and wears to keep it at its maximum efficiency.

Bill