Strange change after battery change

One of the pet peeves about my car has been the fact that ever since it was new, my XM radio (plugged into the cigarette lighter) would shut off when I restarted my car after a short stop. It would stay on while the car was shut down and the key removed, but the power to the lighter would be shut off, just for a moment, during cranking. I always assumed that the system shut off power to everything except the starter while cranking. Good idea, but it was a pain to have to turn the radio back on, wait for it to aquire the sat signals again, etc.

My car had been cranking slowly in the morning for about 3 weeks, and a couple of weeks ago, it cranked slowly while warmed up. That got me to take it down to the dealer to get a new battery. $150 later (installed), I drove out with my new battery.

Ever since then, I've noticed that the XM radio stays on during cranking. I love it, but I'm also wondering what caused the change. It's always shut off, even when new. Any ideas?

My best guess is that the radio turned off from the voltage drop on the old battery when cranking.

That makes sense, but ever since the car was new, anything plugged into the lighter socket shut off during cranking. That goes for my GPS also. I always figured that it was a "power conservation" function to direct all power to the starter.

Your thinking makes perfect sense to me, I didn't know you had the car since new and only noticed the difference on a battery change.
(thought it might be a new XM radio thing)

Got me stumped now.........anyone else?

I'm guessing the built in voltage regulator in the XM dropped to a point below it's threshold for generating whatever voltage is needed to operate the circuit... kinda like unplugging your TV, and plugging it back in... some fire back up, some don't...

wonder if there's a menu on the XM you have that can automatically fire it up when plugged in...

As long as I have been driving them, VWs cut off power to everything but essential systems & the starter during cranking (the 'X' circuit). Not sure about the OPs XM box, but everything in my car cuts out when the key is in the 'start' position.

I have a Sears voltage meter that plugs into the cig. lighter that I like to watch while cranking on a very cold morning. It went as low as 9.6V, but never to 0. It's not as accurate as the SCII, but the scan guage won't show cranking voltage because it's still in the sleep mode during those first few seconds.

alphaseinor said:

I'm guessing the built in voltage regulator in the XM dropped to a point below it's threshold for generating whatever voltage is needed to operate the circuit... kinda like unplugging your TV, and plugging it back in... some fire back up, some don't...

wonder if there's a menu on the XM you have that can automatically fire it up when plugged in...

Click to expand...

That's probably what it is, Brian. Since I started the thread, I've been keeping an eye on what it does. Most of the time it stays on through the cranking, but sometimes it doesn't. I've found that if I re-seat the lighter plug (in that mess of wires you've seen in my console), it will always stay on.

I sure wish that car manufactuers would get away from ligher plug power outlets and just put a number of small, standardized 12V power outlets in the dash or along the side where they would be out of the way. Why stick with the big lighter plugs?