Originally Posted by bclexus

All reputable battery replacement service centers will apply voltage in parallel with the car's battery so all electrically operated devices (e.g. clocks) and the car's electronics that have memory chips (that may not retain memory with a loss of voltage) will always remain powered-up. Most of today's memory chips do retain their memory with loss of power, unlike years ago. However...

To try to answer your question as best I can; I am unaware of anything, with the possible exception of the analog dash clock, that may need to be reset if power (voltage) is momentary lost. That said, it is my understanding that most vehicle's ECU is purposely designed to lose its memory after being powered-down for an extended period of time (say 30 minutes or more) so it will purposely automatically reset itself. To my knowledge most items like seat memory settings, AC control settings, radio, etc. would not lose their memory nowadays if power is briefly removed like when replacing a battery. However, it is always best to keep the car's electrical system powered-up when replacing the battery so there is no problem.

It should be noted that some vehicles are more prone to have issues with the engine's throttle body operation after the ECU resets from lack of voltage for a while, where the throttle body must be cleaned - otherwise the engine might not start, or if it does start the engine will likely idle and perform poorly compared to how it performed prior to voltage being removed.

Rarely will jump starting cause the types of issues mentioned above...unless the vehicle's battery was completely dead.

Originally Posted by drgrant

Thanks. Reason I ask is by the time I have to replace my OEM battery in a couple years, I'll end up doing it myself, just was wondering if there were any caveats to watch out for. I know on another thread here some dude had to reprogram his window switches, but this was pretty simple, just lower and raise each window from the drivers console and they "relearn".

-Mike

Originally Posted by OneFunGS

I've got to say that I have never had anyone install a battery for me. I am not paying for such a simple job that a monkey could do with a 10mm wrench. My $.02

Originally Posted by OneFunGS

So I had my battery tested today as I suspected a problem with it and we are coming into winter. The battery was reading low voltage so I had it replaced. It is a PITA to replace yourself as I helped the Auto Zone guy replace it.

Originally Posted by OneFunGS

Some servo clicking behind the dashboard like the servo is trying to fire but nothing. Just one small click.

Originally Posted by bclexus

Ah ha! So you had a monkey replace your battery after all...

Originally Posted by bclexus

You better hope one of the AC system damper door's servo motor/gear assembly doesn't need replacing...oftentimes it means pulling off major pieces of the dash to get to the servo assembly. The clicking noise is what it sounds like when the servo gear is stripped or has teeth missing. It is very likely that the AC 75° reset issue and the damper door servo assembly are connected.

► Servo Motor/Gear Clicking Noise

Originally Posted by OneFunGS

Okay. I hooked up my Carista today and pulled quite a few codes. Mostly all the AC Servo faults and an AC Amplifier fault. i posted that service bulletin earlier in the thread here and I believe that will be the issue. $450 part.

Originally Posted by OneFunGS

Quoting myself on this one. Got in my car this morning after clearing all those AC fault codes and replacing the battery and now the rear climate control works!

i also had a problem where it was blowing a ton of cold air in my face even in heat mode and that is fixed as well.

If im a logical man, it seems like the battery’s low voltage knocked out some of the AC servos and Amplifier and then stayed knocked out until I cleared the codes and they tried again. Now they are getting proper voltage and working again.

Geez the woes of technology in cars.

Originally Posted by OneFunGS

Quoting myself on this one. Got in my car this morning after clearing all those AC fault codes and replacing the battery and now the rear climate control works!

i also had a problem where it was blowing a ton of cold air in my face even in heat mode and that is fixed as well.

If im a logical man, it seems like the battery’s low voltage knocked out some of the AC servos and Amplifier and then stayed knocked out until I cleared the codes and they tried again. Now they are getting proper voltage and working again.

Geez the woes of technology in cars.

Originally Posted by twylie

Thanks for the follow-up. It is surprising that a low or under voltage situation could send something like HVAC offline, but I'm sure the engineers have a reason it's like that. Glad you got it sorted for no more than the cost of a battery and some time.

Originally Posted by OneFunGS

Thanks. Frustrating as hell and I would never have thought that just clearing the codes would have worked. Especially because there was no check engine light and nothing indicating there were faults. I scanned it out of curiosity and fixed it! Sometimes curiosity saves the cat some money lol

Originally Posted by bclexus

I'm curious 'why' the car had so many AC system related codes too. Just a weak battery should not have caused problems with the AC system where codes are thrown and the system goes into a safe mode. I don't doubt that clearing the codes brought the AC system back to a fresh reset, but I suspect there is more to the story that explains what really happened - that doesn't have anything to do with a weak battery in my opinion... I hope it remains working as it should...

Is there anything in the Lexus service history for this car that may offer a clue about what happened?

Originally Posted by bclexus

I'm curious 'why' the car had so many AC system related codes too. Just a weak battery should not have caused problems with the AC system where codes are thrown and the system goes into a safe mode. I don't doubt that clearing the codes brought the AC system back to a fresh reset, but I suspect there is more to the story that explains what really happened - that doesn't have anything to do with a weak battery in my opinion... I hope it remains working as it should...

Is there anything in the Lexus service history for this car that may offer a clue about what happened?

Originally Posted by OneFunGS

Thanks. It is interesting. I’m thinking the low voltage and the 3 zone, 2 blower system in the luxury package has something to do with the system going into safe mode. That and a loose ground I found a few days ago on a fuse box (I lost turn signals and went hunting)

service history is clean. Car was garage kept and never driven (which might have caused more issues than not)

im hoping the system is all set now as even when I started the car today the system booted and remembered my settings. So alls well that ends well? Lol

Originally Posted by bclexus

That kind of stuff just doesn't happen...unless there is a good reason (cue conspiracy theory) - like the car has been in a wreck and repaired, been flooded, etc. As I said - I think there's more to this story...