anc4

can you enlighten me as to how to get at the relays under the subwoofer (removed all the plastic bolts but couldn't lift out the subwoofer assembly) and the trunk relays?
i charged both batteries and brought them in for load testing and they passed.
drove the car for 20 miles, left it in the garage for 2 days and same issue.
front battery reads 12.4 engine off, 13.7-13.9 w/ the engine running. the rear is 5.4 before i start the car, then goes to 13.7-13.9 w/ the engine running.
this is not an alternator issue, there is some other issue here, a relay or control module.
frustrated as this garage queen needs to stretch it's legs and if it sits the remotes won't work. this is fine for me but not for my wife!!

kbob999

The subwoofer has 3 nuts to remove, 2 on the left, one in the hole on the right, that have to be pulled. Unplug the wiring, then it is free to come out, but it does not come out easily.
If you lift the woofer, and bring the bottom out first, this seems to work the best. Be creative and persistent...it does come out.

Regarding the fuses. The large one (200 amp?) supplies juice from the alternator to the rear, and the smaller one (100 amp?) feeds juice from the rear to the starter battery.

Seeing that both of your batteries read correct voltage with the engine running, I predict that your juice is flowing both directions, and your fuses are fine. Since you almost have it apart, you might as well check continuity of the fuses while the woofer is out.

More than likely you have a drain somewhere that is causing low voltages at the rear convenience battery. The only other options I can think of, are the relay next to the battery control module, or the BCM itself.

Keep us posted on the results. I'm working through a similar issue with lack of charging, and have 3 items left to check in order of cost: the relay, the alternator, and BCM. I'll let everyone know what fixes it too.

cyglee

anc4: do a search for "dreaded red battery icon-" it talks about the subwoofer removal, and passenger floor fuses. But, I'm thinking you have a electrical drain, as the car sits for 2 days. Are you using a cTek regularly? The K57 relay I replaced is with the battery control module in the right side trunk. I pulled the trunk lining back to check the BCM connections, and as the relay was ~$35., I figured to switch it out before putting that liner back.

anc4

i was using the ctek regularly but i think it's crapping out. it's making funky noises that it has never made before! is there a way to test the ctek, or just purchase another?

kbob999

I'd get another charger if it's doing funky things, or not charging your battery.

To follow up on resolutions to my red battery warning...it was the alternator.
Even though it was only 12 months old, and looked fine, it was DOA. Since Autozone has a lifetime warranty, I have a new one coming in 2 days at no charge (no pun intended).

I did buy a used relay for $10 on eBay, but that did not solve the issue, so I have a spare just in case. I was hoping it was not the battery control module, which was not the case when the alternator was found dead.

An hour of fiddling and I'll be back to normal.

cyglee

kbob: so, what voltages did you measure (when running) at starter battery, and consumer battery with the bad alternator?

kbob999

I had my rear battery on the charger, which measured about 13 volts hooked up.
Unconnected, with car running, was 12.3 volts most of the time, and didn't waver much.
If I went for a drive, it would throw the red battery warning, and start shutting down Comand and saying STOP - BRAKES as the voltage dropped and it thought the SBC was going down.
The starter battery continued to drop too of course, but always cranked the car.

anc4

so i do my usual morning routine - go into the garage and measure the voltage of both batteries. at first the consumer appears dead, window doesn't go down the 1/4" when i open the door and i can't open the trunk. i put the key in the ignition and the car comes to life, i don't start it, but it's like a switch went on. the window goes down the light come on and i can open the trunk. i measure the front battery -12.3 and then the back 11.8, as i'm measuring the back, consumer battery, i hear a click and the voltage starts decreasing .1 for every second!!!! what the f is going on hear (can you hear lombardi saying that?)
any thoughts please.
i'm wondering if the system turns off the consumer battery if it goes under a certain voltage, i haven't had the ctek on the consumer battery for 1-2 weeks

bobterry99

When you turh on the ignition the vehicle power supply module reads the voltage on the Consumer battery. If the voltage is less than 10.8 volts, then it energizes a relay that connects the Starter battery to the Consumer battery. If the engine is not started the relay turns off after 30 seconds.

anc4

and does that relay turn off the connection to the consumer battery prior to me turning on the ignition? possibly due to the consumer battery voltage decreasing below a certain threshold?

bobterry99

No. The check ov the Consumer battery voltage is made when the ignition is switched on, and the relay will de-energize after 30 seconds if the engine is not started.

anc4

interesting, my consumer battery is getting turned off after sitting for a short time, could this be a problem w/ the relay you've mentioned?

bobterry99

The Consumer battery is directly connected to the alternator and power to every electronic module in your vehicle. That relationship never changes, so it is impossible to turn off that battery. On the other hand, the Starter battery is electrically isolated from everything but the starter motor and the vehicle power supply module -- unless the previously mentioned relay (K57) is energized.