battery to protect user changes

However, suppose you want to remove an airbag connector. In that case you first need to disconnect the 12V battery and wait a couple of minutes so that the SRS ECU will not have any power available. For that job, you would not want to try to keep user settings intact by having an auxiliary power source connected.

 

This is true. It should go without saying, but if you keep the 12V system hot, all of the unswitched 12V power leads are hot. Kinda obvious, but sometimes we need to point out the obvious to save people from themselves.

Don't allow anything on the + side to touch anything grounded, which means keep the red wires away from the chassis.

Tom

 

I think you will find the 9V battery can -easily- handle the "keep alive" current in the Prius. Unless the brake booster fires. It does so even if the car is not on, particularly if the car senses the fob in proximity. It goes into "get ready" mode. If it fired with the 9V battery only connected it would probably loose all settings.

ALWAYS remember, you DO NOT control the cars systems. You only -INFLUENCE- what happens.

 

yeah i was probably referring to the 90 seconds of backup power the prius has to the SRS system when you disconnect the 12v
and the 5 minutes of back up power in the high voltage electrical system after you disconnect the hybrid battery


i guess i mean nothing could happen, but the power is still there

curious people will want to keep alive their settings (clock, radio, reverse beep, seatbelt beep, auto window), probably
only takes 5 minutes to restore all that, heh

ive lost my radio presets 5 times by simply playing a scratched/dirty cd, in full ready mode!

the garage door opener and phone book are NOT lost when you disconnect the battery, thank heavens

 

Aren't the other systems on the ignition side of the circuit just like the cigarette lighter?

 

Hi Pat,

A few miscellaneous circuits remain powered up continuously. For example the engine and hybrid vehicle ECUs receive power continuously to preserve learned settings. The coolant heat recovery system relay (which your car doesn't have) also has 12V available at all times.

Regarding rigormortis' reference to disconnecting the traction battery, the reason for a wait period is to allow the electrolytic capacitors in the inverter to discharge, prior to contacting the high voltage battery cables.

Regarding SRS, it appears that system receives power from IG2 which is a switched circuit and should turn off when the car is IG-OFF. I suppose that the repair manual advises disconnecting the 12V battery to be ultra-cautious. The SRS has a backup system that can provide power for a 90 second period.

 

Sigh.

No. This is NOT safe! To be safe, you must do one of two things:

1) Use a current limited source of 12 Volts. That way, if the positive battery cable (from the battery you remove) touches ground, it simply shorts out the current limited 12V supply. You will lose your presets, but there won't be sparks, blown fuses, and general mayhem.

OR

2) If you insist on attaching a "basic jump starter" to the 12V post under the hood, then immediately upon removing the cable on the positive post of the aux 12V battery, you must ensure that it is electrically insulated from the chassis of the car and can't possibly make contact. If it does, it's a direct short of the jump starter to ground - easily 100s of amps will get pulled. At best, you'll blow the expensive 100 amp fuse.