Low Voltage in Rear Power Outlet

This dealer says the battery is fine and they're too busy to diagnose why low voltage on the 12V outlets. "Besides," service advisor says, "it's normal for voltage to drop when you're using power. The car is doing lots of things with that power and it can only supply so much."

They were very dismissive and made it very clear that they were not interested in helping. This would be Crown Toyota in Ontario, CA.

I had a sinking feeling this was going to turn into a battle with Toyota, and none of this experience so far is assuaging that fear. I won't even be able to lemon law the car if they don't fix it because it's not making the car undriveable.

EDIT - The service advisor called and explained that Toyota warranty does not cover diagnostic labor, so if I want them to look into the problem it's going to be out of my own pocket. I guess I know what dealer I'm never going to for service.

 

Toyota dealer #1


Toyota dealer #2


Who to believe? <-- That's mostly rhetorical. If they'd even tried to load test the battery there's no way they'd have passed it. Even a $2 Harbor Freight multimeter shows the voltage counting down like a SpaceX launch when load is applied to the battery.

 

Found this post that seems to confirm that behavior. Reading through the forums more it seems that low 12V battery is a common issue with the Prime.

 

It is interesting to me that there are a half-dozen or so different threads I've come across where different people report that their brand new Prime's 12V battery is dead, or very low.

 

I suspect in my case that the battery just sat for way too long in the dealer lot. As I've been driving I've been having less and less low voltage "incidents." I suspect the battery is getting charged up over time. Perhaps the charging system is thrown off by a battery that's been discharged beyond a certain point.

 

Well, the low voltage at the battery seems to have gone away. The problem is that the 12V outlets still show a voltage sag under load that is entirely consistent with a 10-foot run of 22AWG from the fuse box to the outlet. Here's the measurements:

Open Circuit 13.5V
0.5A 13.3V
6.5A 11.4V

While one outlet is experiencing the voltage sag, the other still reads 13.5V open circuit, so it's not dragging down the whole system. That means we know the problem is between the fusebox and the outlet.

Now I need ideas for load testing that doesn't involve my inverter, so I can rule it out as a factor. I have already tried three different 12V plugs to rule that factor out. If the wire isn't really 22AWG or smaller, the only other thing I can think of would the that there's something wrong with the outlets themselves.

The one thing that's confusing to me is that the voltage is variable. Sometimes it's 11.4V, and sometimes it's ~10.2. The multimeter shows it constantly fluctuating up and down.

 

I have an idea: My inverter came with some cables that clamp directly to the battery. I can test the performance of the inverter and the voltage when directly connected to the battery to see if I get the same voltage sag, or not.

 

Crap guys. I just realized why Toyota says to limit the use of the outlets to 120W. We all thought that meant a 10A load, but I think Toyota knows about the voltage sag. Guess how many amps are required to draw 120W of power from a 13.6V power source through a circuit with the resistance I'm seeing? It turns out that you'll need about 12.5A. Now doesn't it make sense that the outlets are fused for 15A? It just turns out that 12.5A is 83% of 15A. Does that number sound familiar? In electrical engineering it is common practice that fuses are limited to operating at a continuous current equal to 80% of their rated capacity.

I really hope I'm wrong. If I'm not, it means the only fix is going to be rewiring the car. On the other hand, does anyone know if Toyota has technical specification on the minimum voltage of the 12V outlets?

 

Sorry for all the spam replying to myself, but I have an interesting update (to me anyway). The dealer called me today to let me know that they're still trying to get a battery, but that they are now being told they are on "national back order with no ETA."

"Maybe there is something wrong with them," the service manager told me. Perhaps so.

 

Got a call from Toyota USA today: still no 12V battery anywhere in sight. Not sure how long to wait without the use of any 12V accessories before stepping up my insistence that they fix it immediately.