Ignition short - 12V drain? Transmission? 12V's charged. No error codes but Pkg Bk is not sensed

Since your reported symptoms 1 and 2 sound like a weak 12V battery, I would suggest that you reconsider your assertion that the installed battery is charged and good. You can measure battery voltage when the Prius is IG-OFF to confirm or refute that assertion. A new AGM battery at 100% charge will measure 12.9V.

Regarding #3, typically the factory fog lights will not operate unless the headlights are on - unless you implemented a modification to the wiring.

If you are able to confirm that the installed battery actually has a good charge, I suggest you disconnect the negative cable where it bolts to the body for a few minutes to allow all ECUs to reset. Then reconnect and see if that makes any difference to your symptoms.

 

Yes.

You also might check the tightness of the battery cable connections to the battery as well as the negative cable connection to the body.

 

Thank you for this thread. I have a 2007 Prius, 65K miles, and a NEW Optium yellow top battery installed in August 2012. The battery appeared to be healthy and functioning normally until ~ 2 weeks ago. Since that time I'm consistently seeing symptom 2:

This symptom is usually accompanied with 'pulsing' in the brake pedal at startup.

I've only seen symptom 1 once after presumably draining the 12V battery by powering into Acc-only mode (or whatever comes before 'READY' mode) and using the MFD in Maintenance mode to check the 12V.

And for the record, my model does not have fog lights, so strike symptom 3 for me.

I have attempted to charge the 12V battery with long trips of 3 hours or more and even keeping the car in Ready mode in the garage for 4 hours. This temporarily solves the issue, but after a day or so the Red Triangle at startup comes back.

I have not yet checked the battery connections (thanks for the tip!) or checked fuses.

I'm wondering what, if any, 12V battery loading might be causing a "vampire draw" while the vehicle is powered off.

 

I suggest you consider the most likely possibility, which is that your 12V battery may have failed (regardless of how new it may be or its brand name.) Measure voltage across the battery after the car has been IG-OFF overnight.

To determine quiescent current draw, you would need to connect a digital multimeter set to read current, in series with the 12V battery negative cable where it connects to the car body. Position the meter so you can read it with the hatch closed. Close the hatch and doors, lock the car, place the fob at least 15 feet away from the car. Then see what the current reading is. If much more than 20 mA (or 0.02A) then you have a problem with excess current draw.

 

This occurred to me as well. What voltage reading would indicate a failed 12V battery?

Thanks in advance.

edit:

Does a FOB kept within the vicinity of the car drain the 12V?

 

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A new fully-charged AGM battery should measure 12.9V. If the voltage is 12.2V or less then it needs help or replacement.

Well, it doesn't "drain" the battery but it will result in a much greater current draw. A Smart fob located nearby will be in two-way communication with the Smart system in the Prius. The skid control ECU will run the brake actuator to ensure the brake hydraulic system is pressurized, in preparation for the car being driven. If you want to see what the quiescent current draw is, you should keep the Smart fob well away from the car so that these systems are not provoked to run.

 

Patrick I do not know how many different models of the gen2 Prius there are but the UK/EU version does allow use of the fog lights with just side lights may be different in US. To only allow them to work with the headlamps would defeat there purpose and make them useless.

 

Checking the US wiring diagram shows the ground return for the fog light relay is controlled by the body ECU at pin 17 so it is not clear how they operate in the US.

 

Any further report? It is always helpful to learn how others problems were resolved.