Gen 2 Prius Won't Start-not the 12 V Battery

If your headlights don't work you have a problem with the 12V system in the car. The 12V battery will allow the headlights to turn on regardless of the "Ready" state of the car. I'd start by checking the 12V battery and its connections, especially where the negative 12V battery cable bolts to the body. New batteries can be defective, or you might have a bad battery connection. If that checks out, check the 12V voltage at the underhood jump point with a multimeter and see that it matches what is available at the battery terminals. If that matches, you probably have a problem with a fuse or the wiring beyond the jump point.

 

Hmm. Check the 12v battery connections at BOTH ends; especially the neg. to the frame (it's hard to see and reach). It's either an 8 or 10 mm bolt head.

I guess you're not hearing any relay clicks from the HV battery when you try to start the car?

 

OK, as I like to say, a hybrid is an electric vehicle and the state of health of BOTH batteries is paramount. Seems 12v is fine so suspect HV battery next. Rebuilt batteries are still old batteries.

GOOD LUCK!

 

Well the 12 V SYSTEM is not fine if the headlights won't come on.
AND the simple fact that the battery is new proves NOTHING about it's health or state of charge.
It also proves nothing about the main 12 V cable connections.

Before he junks the car, he should at least put a meter on the battery and/or connect it to a charger overnight.
And check those cable connections too.

We are 25 posts into this thread and I think that has been suggested about 3 times now......with no response from the OP.

 

12+ volts is not necessarily good. a new battery is 13 volts

more importantly, what is the exact voltage, and what does it drop to after the headlights have been on for 5 minutes?

 

That's plain weird. You mean that literally, as in the reader does not power on? It would be good to get a reading of that voltage while you have the reader attached. (Which could require popping that diagnostic connector out of its cutout in the dash, and using a backprobe.

Yeah, they just don't break that often, though. For some reason the computery thing is always something people want to suspect, but it's also the solid-state no-moving-partsy thing and problems usually turn out to be somewhere else.

 

Your 12v battery is good, no need to keep going on about this non issue. At this point it's also shouldn't be the hybrid battery cause it's not even getting to the point of the car needing it to start the car.

Just for fun, replace the AM2 fuse (the one you checked) and see if anything changes.

I'm still suspecting rodents ate some wires

Matt at Texashybridbatteries.com is an expert here on the forums. If he's not far from you, maybe you can give him a call. He will know how to troubleshoot the car and he will come to you without you needing a tow

 

Yep. Could be.

The + on your 12+ readings is really important.

If there is no load on the battery, it should read about 12.8 volts, assuming it is an OEM AGM type.
12.0 is a bit more than half discharged and may not be enough to work right when a load is applied.
With no load, anything below about 12.4 is suspect......as it might go WAY down when a load is applied.

 

Nope. Sorry. The 12 V battery system has not yet been proven good.
Still could be a weak battery or a bad main connection.

 

get past it already, read post #29. He bought a new battery and he measured over 12v. What more do you need?

 

"Over 12 V" is not accurate enough.
And there are other things that can cause low voltage......like corroded connections.
If "getting past it" means thoroughly testing and inspecting it and THEN moving on......I fully agree.
OTOH, if it means ignore that because of assumptions.......that is not good practice.

 

When you press on the brake pedal, do you see the brake lights light up?