Symptoms of dying auxiliary battery? Puzzled.

Hi all,

Symptoms:
1) A month ago, our key fob began to sporadically not unlock the car remotely. It got worse and worse (resorting to manually unlocking the car w/ the metal key), then after a while, it also stopped locking the car remotely, altogether. Both functions lost now.

2) Around that time, there was an episode where the car would not start with the key fob in the slot or remotely. Then when it finally did after many attempts, it would not shut off using the Power button. I pushed the 'Key' button in (located under the steering wheel), and now it start up/shuts off normally for the past several weeks, no problems.

3) I replaced the key fob battery, but the remote access issues still persist. The small red light on the fob lights up when I press the lock/unlock buttons near the car, but to no effect.

4) This past week, my wife was pulled over since the driver's side brake light was dim. We noticed this before but it was intermittent. All the LED lights are together dim or bright as the other, but it's off and on.

5) The dome light above the back seats was stuck on last week. We've had to remove the lightbulb to temporarily resolve it.

6) The clock doesn't light up at all and stereo system are dead now (whether car is running or not). The 'Add Fuel' warning nearly always is flashing. When you start driving, the Consumption miles is always back to '0 miles'.

7) The car-door unlock/lock button won't work properly unless the car is turned on.

8) In ACC mode using the multi-screen display, the auxiliary battery voltage is 11.9V, which seems borderline. Using a voltmeter, I manually read a voltage of 12.6V with the red/black terminals still connected to the car, which was off.

Background:
- 2005 Prius,
- bought used a year ago May,
- No idea when auxiliary battery was installed.

Dx:
If it was a dying auxiliary battery, wouldn't driving around charge it up and resolve these issues?

Just hoping it's not an more intricate electronics issue ...

Thanks!
David

 

Thanks Kevin, there's 160k miles on the car.

Are ordinary voltmeters not sufficient, or they have the specs on what the voltage should read for each model of battery? What is the expected new voltage?

 

Hi all,

So I put down $150 on Amazon for Optima Batteries 8171-767 (DS46B24R) YellowTop Prius Battery and replaced the battery this evening ...

Issues persist - unfortunately, none of the above symptoms are resolved.

Any further ideas on this one?

The $80-90 to have Toyota look at it is becoming more of a possibility, as difficult as it is for my DIY brain to think it.

Thanks,
David

 

Yes, no corrosion or loose connections.

A couple days ago, I took the old battery (within Prius) to AutoZone to be tested. They left the battery in the car while performing the load test, and indicated the battery was bad.

I should note that the MAINT REQUIRED light is on solid. But it's about time when I replace the oil filter.

 

VICTORY! Haha!

I started Googling on just the clock/stereo dead issue, and found another person solving their problem on a Corolla by replacing a fuse.

So I found the 2005 Prius fuse label, and located the fuse which best describes my problems (location 39, a 15A fuse): Radio fuse or fuse diagram | PriusChat

39. DOME 15 A:
Audio system, interior
lights, smart entry and start system,
gauge and meter, turn signal lights,
luggage room light, clock

I replaced it with the spare 15A fuse located at position 24, and Whala! Key fob, clock, stereo, dome light all work!

The original fuse is severed for sure, per the photo.

So glad this is resolved. And now a new battery to boot, what's more.

Thanks all!

 

Patrick,

The dome issue description was relayed to me through my wife, and something must have been lost in translation. It wasn't verified as other issues which were conducive to quickly confirm.

When I replaced the fuse the dome light fired up instantly suggesting that, on the contrary, the dome light was out cold until the circuit was operational again.

My approach is that some diagnostic cases reveal some issues as red-herrings which appear to contradict the eventual logic of the fix.

To bear through the cognitive dissonance, apply Occam's Razor and explore all the possible fixes for the most issues helped in this case?

I worked at a small engine repair shop for a few summers - it became apparent that some engines had everything in place but could not fire up at all, while others, which didn't seem to have a chance, which did. Very frustrating at times.

Experiencing it all without omniscience, I've relinquished it to both a science and an 'art'?

Thanks for reading my soliloquy,
David