Electronic Fault in the START system?

[DeadPhish]

I've noticed four times over the last week that when I shut down my Prius that it immediately comes back to life in Accessory Mode??? Weird, this never occurred before.

The Fob is always in my pocket. I hit Park then Power OFF but it will sometimes go OFF then right back to ACC mode. If I power on with my foot on the brake then power OFF again it stays OFF.



I'm thinking ...

1. 12v battery is getting low and screwing with the electronics
2. a faulty sensor
3. a low battery in the Fob
4. a traction battery beginning to act up..doubtful

See details of my 05 in my sig. Does anyone have any experience with a situation like this?

[richard schumacher]

Data trumps (or at least informs) speculation :_>

If the little red LED on the fob no longer flashes when you press a button the fob battery should be replaced.

Test the 12V battery, either
- with a voltmeter at the jump point under the hood; with the car OFF it should be between 12.5V and 12.8V. If it's less than 12.0V it should be replaced.
- using the self-test procedure shown here:
http://www.myhybridcar.com/forums/to...ry-health.html

[DeadPhish]

Originally Posted by richard schumacher

Data trumps (or at least informs) speculation :_>

If the little red LED on the fob no longer flashes when you press a button the fob battery should be replaced.

Test the 12V battery, either
- with a voltmeter at the jump point under the hood; with the car OFF it should be between 12.5V and 12.8V. If it's less than 12.0V it should be replaced.
- using the self-test procedure shown here:
Checking 12v Battery Health - Hybrid Car Forums

The fob on my 2005 doesn't have an LED indicator of any kind.

I ran the above procedure and found the following
step 1 at ACC only the battery was at 11.1-11.2 v
step 2 with a load on it... i didn't write the values down
step 3 with full power on the battery reading was 14.1-14.2v

additional data:
randomly the clock will reset to the default of 1:00

From your criteria it does seem if the 12v is giving up the ghost, no?

[qbee42]

A good battery should be at around 12.8 V when not being charged. Yours is too low.

Tom

[timberwolf]

For your step 1), mine readings vary between 11.9 to 12.1 which has done from new. The test using the MFD still puts a load on the battery, and those figures that Richard quotes sound like the voltages that you'd only get with the car completely off and using a Digital Multi Meter measuring at the battery terminals.

[richard schumacher]

The ACC load should be less than one Amp, which a good battery would barely notice, so I strongly suspect a failing 12V battery. If you can borrow a voltmeter, the jump point voltage with the car OFF would settle it.

[hschuck]

Originally Posted by DeadPhish

The fob on my 2005 doesn't have an LED indicator of any kind.
. . . .

The indicator is difficult to see when not activated. Hold the fob so that the lock button is at the top. The indicator is to the right of the lock button on the raised bezel. It should illuminate when one of the buttons is pressed; if a smart key fob it will also illuminate when communicating with the car.

[Celtic Blue]

Originally Posted by DeadPhish

step 1 at ACC only the battery was at 11.1-11.2 v

That be D-E-A-D, dead, deceased, no longer amongst the living, an ex battery. Whenever I have a vehicle battery in that range it begins behaving more as anchor than as power storage device. They don't rehabilitate well either.

[timberwolf]

Originally Posted by richard schumacher

The ACC load should be less than one Amp, which a good battery would barely notice, so I strongly suspect a failing 12V battery. If you can borrow a voltmeter, the jump point voltage with the car OFF would settle it.

How much of a volt drop would you expect to see with the MFD method compared with a digital voltmeter measure the battery not under load? 0.5 volts?