Hybrid Battery Low SOC

I had an odd occurrence last night on my 2016 Two where the hybrid battery state of charge dropped below 20% and the drivetrain was reluctant to move the car. I stopped to pick up my mail at the end of a day of driving (about 180 mile round trip) and left the car in Park with parking brake set for the time it takes to walk to the mailbox. When I put it in Drive the car was reluctant to move up the slight driveway incline and I got a brief message that the hybrid battery was low. I've got a ScanGauge hooked up and noticed SOC was about 20% - normally never goes below 40%. I live at the top of long hill and usually the SOC is about 60% when I pull in the driveway. I had not looked at the battery status but the car was performing fine up the hill until I parked.

The drivetrain would initially not engage with increasing engine RPM, then catch and surge ahead. Limped up the driveway and watched it for awhile in both Drive and Park and took a couple of videos. The engine RPM was hunting a bit, the hybrid diagram showed engine charging the battery but with no increase in SOC, which bottomed out around 18%. Battery temp was around 90F, more or less where it had been most of the day. Unfortunately the X-gauge codes for battery current are not working so I couldn't see that. Aux battery voltage was 14.4, charging normally.

I did a couple of restarts and the hybrid battery finally began to charge. I shut down once it was approaching 40% and all was fine in today's driving.

I did a Gen4 forum search on this and saw a couple of instances blamed on extended time in neutral but nothing like this. Any thoughts?

Thanks -

 

The car has about 53000 miles. Just bought it off-lease in October, all service records included and showed no hybrid issues.

Yes, good question about loads. It was night and dry, so only lights and low heater fan.

Aux battery seems OK - I've been watching charging currents and voltages and they seem reasonable. I did check it during the episode and it was typical. I just looked the video I took and at the lowest 18% SOC the hybrid battery voltage was ~203-5, basically open circuit voltage for the NiMH pack so not abnormally low.

The only other clue was in stop & go traffic after a 90 mile run** and one stop/restart. Creeping slowly in heavy traffic I noticed the engine was starting and stopping briefly and repeatedly when it typically would have stayed in EV. But sometimes the hybrid system just capriciously defies typical behavior so I didn't think much of it. My attention was outside then and also for the 5 minute drive home from there, so I didn't catch any early signs that charging was abnormal.

** BTW, 55.5 mpg on the ScanGauge for a 180 mile round trip, with Michelin X-Ice snow tires, temp in 40s! Mixed interstate and open 2-lane, some city at both ends. I was pretty pleased.

- Tom

 

No codes set or pending.

Thank you for the heads up on the service bulletin. The symptoms do partially match. I just downloaded it and will check the status of this car.

- Tom

 

It took me a long time to follow up on this with Toyota, but the short version is that the service bulletin noted by Elektroingenieur fixed the problem. It got much worse in spring and early summer, and eventually left me partially stranded on a hill until the hybrid system decided to start charging again. Expanded symptoms are: 1 or 2 bar battery level, engine revs but does not charge the battery or accelerate the vehicle. With ScanGauge I saw SOC levels as low as ~20%. The local dealer did the software update under warranty and no problems since then.

 

Forgot to say Thanks! This tip really helped!

Tom