Startup/Shutdown Sequence Collapse. Won't Start.

Hi Folks:

Been having this problem get worse for some time now. I've been bridging the problem by monitoring it with a DVM and making use of a Lion jump start kit. With an increasingly frequent occurrence I've noticed both the startup and shutdown sequence collapsing. Everything just turns off and you won't hear the full sequence of relays or displays and cabin lights. On startup the main sequence is the HUD comes up, the radio comes up (usually having lost the last channel but sometimes not), and you don't hear the relays in the traction battery kick in. Then everything shuts down. Another lost sequence is on shutdown which usually has quite a few relays click and a sequence of interior lights coming on. In a collapse you'll hear the relay in the traction battery click then then everything collapses.

In order to restart the vehicle I'll have to use a Li-ion jump kit. Sometimes startup up is very troublesome. The HUD will come up, and the radio will as well. The traction battery sometimes won't click in and the system shuts itself down. During this intermediate state, I get the full Christmas tree light display on the HUD. Sometimes the radio will cycle its power several times, and when this happens I won't get a successful start. The brake may
force itself out of being pressed before shutting itself down. It may take several re-jumps before I can hear the relay in the traction battery kick in and I probably will get a successful startup and the car will drive. A recycle of the jump system requires me to disconnect the L-ion kit and reattaching it. It has it's own set of relays.

Thinking this might be an AUX battery issue I've been checking the jump terminal voltages before a start and after a shutdown and I'm seeing normal voltages of 12.5 to 12.7 volts. During some drives I've been using a limited functionality OBD2 reader that displays the 12.5V bus voltage and I see it going all the way to 14.2V, so I think the AUX charging system is working. Complicating that, after the shutdown collapse that just happened, I monitored 2.5V on the jump terminal on a verified DVM.

I'm thinking it's a relay/contactor in the traction battery getting sticky and requiring more current to switch. Or another relay in the chain. Of course this 2.5V reading might complicate that conclusion. Perhaps the aux battery really is bad. I got the first battery in Jan 2021, but had to swap it out in May on warranty replacement. Did I get unlucky again?

Anyone have any insights on this? Is there a good schematic of the power relay system and a description of the startup and shutdown sequences?

Andrew Tubbiolo
2005 Prius
48 MPG 257000 miles.

 

I did a load test at the auto parts store. I had similar issues, but I could see low voltage on the battery back then. Most of the time, my voltage tests show 12.5V to 12.7V.

Andrew

 

I tested the car again this AM. 2.1V at the jump terminals. I used the L-Ion kit to charge the system to life so I could open the hatch back. After disconnecting the charge kit, I disassembled the hatchback so I could reach the aux battery and it showed 12.6V. So some sort of electronic equipment lies between the aux battery and the charge terminal? Mechanical connections were good. Looking forward, I could see the FOB beacon indicator on the hud. Wondering if the car might start, everything collapsed as soon as I pressed the brake pedal. The voltage at the jump terminal 1.8V. I'll have to disassemble the back end to try this again so I can look at the battery terminals again. Maybe the aux battery can only hold a surface charge and several of the plates are broken collapse on any appreciable current pull?

After using the L-Ion jump kit to recharge the system I disassembled the hatchback to get back at the aux battery. I disconnected the L-ion jump kit before checking the battery terminals. The jump terminals read 1.8V. I then checked the hud and it was blank. The battery terminals read 12.6V. Sometime between me traversing to the front of the car to re-check the jump start terminal, something kicked in and now the jump terminal read 12.6V. I was able to do several power cycles on the car. So the question is what lies between the aux battery and the jump terminal?

Andrew

 

No water in the battery well. Just looked at it. all mechanical connections survived a pretty powerful tug test. Anywhere I could find a schematic of the 12V system? The battery was new in May 2021. It seems fine.

Andrew

 

I'll check this out. Thanks.

Andrew

 

Checked the ground connections in the back around the aux battery. Gosh everything was tight.

Andrew

 

One more observation. I was able to connect the jump Li-Ion battery, but disconnect it from the system before attempting a start. And it was a successful start. Again, I think something lies between the aux battery and the rest of the system. Obviously I need to look over a schematic to understand what's going on here.

Andrew

 

Tight and clean. Nice metal on metal connections.

Thanks.
Andrew