Is my traction battery going bad?

Has anyone else experienced anything like this before? A 10-12 mpg drop over 500 miles or more, then returning to normal?

 

I replaced the 12V battery in 2014 after which there was no change in mpg.

The next time I disconnected the 12V was after the low mpg problem came up. I cleaned the HV fan and dropped a plastic clip behind the 12V and had to take that battery out to retrieve the plastic clip.

So in this case it was not related to disconnecting the 12V battery.

 

EB, That all makes sense. Loose or corroded connections could be at fault here given the range of issues we've experienced. Too bad our cable and software didn't show up when the car was misbehaving.

One factor that could come into play, and aggravate loose or corroded connections, is the weather. Of course being in California we haven't had any significant rain since April (less than 1/2 inch in May, June, July). However the temperature cycles come close to matching the car's behavior.

We had over 105 degree high temps for about three weeks in a row. Then a few days ago the high temps dropped into the high 80's to low 90's. It's supposed to warm up again to the mid 100's starting this week. Heat of that kind is rather normal for Redding CA in the summer. I'm not suggesting the heat itself is an issue as this is our 5th summer here. Rather what you wrote + heat could be a potential cause.

At this point I'll wait for the hot weather to see if the poor mpg conditions return. If they do I'll tear the car apart once again and check over the connections.

Thanks for your help.

I drove the car this afternoon and everything seemed normal. The avg mpg on the car's display is creeping back up and is almost to 43 mpg on this third tank of gas since the problem started. The first 1/2 of this tank were in the mid 30's.

I do watch the Prius bar graph SOC and did notice the poor behavior. I've always respected the Prius design engineers for the Synergy drive and Atkinson engine out of which they squeezed such great mileage. I doubt if I have ever ignored the SOC or 5 minute bar graph for a full tank of gas. I don't do extreme hyper-mile'ing but I'm willing to drive 39mph in a 45 mph zone as long as no cars are behind me. My wife thinks I'm crazy. A also do pulse and glide sometimes but never when my wife is with me. So I'm pretty informed as far as this car's behavior.

I have to say again that the Prius is pretty hard to beat from my perspective. The 20 Cu Ft of cargo space simply isn't available in any sedan, and 45+ mpg isn't available in any other car with that much cargo (small SUV). We like the ride, the features, the comfort, the rear seat leg room, smart key system, and of course the $7,000 in gas savings we've had over the years. I would be thrilled if this mpg problem turns out to be nothing more than connection issues.

 

Sounds interesting. Do you know of the name of the app for Android? Is there any other hardware required for this wireless connection?

We continue to have problems but they are intermittent. We still can't get a tank of gas over 40 mpg but often the car is behaving normally. Then for several hours it again faults and we are averaging in the low 30 mpg range. The best we've had for a full tank recently is about 40.5 mpg. I just haven't bothered to hook up the laptop and run the software again. I'd have to catch it when it is failing.

If the app you speak of can be used at anytime without the laptop it would be so much more convenient.

 

Never mind. I found "Torque" and will likely buy the bluetooth adapter. I wish I would have known about this first before burning up so much time and energy on TechStream. This seems like a much better tool.

 

Thanks. That's the same bluetooth adapter I ordered. I'm anxious to receive it and put it to use. Perhaps I'll get somewhere with this new option.

 

I now have the Bluetooth adapter and have been setting up Torque. I'm quite pleased with this setup, I've even ordered a cheap 9" tablet so I can take advantage of the larger display and have more data on the screen. My Galaxy S3 already limits me.

At the moment the Prius is behaving near normal so there isn't much to discover.

It really irritates me that I paid Toyota about $75 to check out the HV battery. All they did was test drive the car for 7 miles, and check for codes. Now that I see the huge amount of data available using Torque paying Toyota was a total waste of money.

 

I had the same thing happen to my 4Runner. The gas cap was broken. I had the SCAN II hooked up in the 4Runner which did a nice job of telling me what was wrong.

 

I thought I'd through in an update. I've monitored the HV battery using the Bluetooth ODB2 adapter and Torque Pro app. I haven't seen anything wrong with the battery, it seems to be working as perfect as I could expect. So I have no idea what is behind the lower mpg.

We are getting normal mpg on 100+ mile freeway trips locked on cruise control going 65-70mph. We get about 48-50 mpg. So I don't think we have a rolling resistance issue like dragging brakes.

Our problems are all around town, typical stops for stop signs and red lights. These are trips that we know well and haven't changed our pattern. Where we used to get 45-47 mpg we are now getting 40-43 mpg. Over the span of about five or six tanks of gas the initial 35 mpg issue has slowly improved to the 40-43 mpg we've seen lately. I have no explanation for this.

To make things more complicated we had to put new tires on the car. They are Michelin Defender ST type which I understand will likely drop our fuel economy by 2-3 mpg. So we'll be watching for 37-40 mpg around town now.

Bottom line. I don't know what is wrong with the car.

I've monitored HV Internal Resistance and HV Battery Block Voltage for all 14 cells.

The only interesting thing is the last two tanks of gas have shown about 4-5 mpg less on the Gen II display than calculations at the pump. Two tanks isn't enough to set a pattern though. Over the years I stopped checking using a calculator at the pump because the result was always within +/-2mpg from the car's display. So being off by 4-5 mpg is far from our historical data. I wonder if there is something in the flow meter that could go wrong and make us think we are getting less mileage than we really are.

 

There is no question the Defenders are smoother riding, quieter, and better handling than the Michelin Energy Savers we replaced. I would have gone with the Energy Savers again but we were up against a wall. I had a nail in one tire that was not repairable. Long story short we couldn't wait 3-4 days so I went with the Defenders.

My intention is to buy a Gen IV as soon as they are available so the loss in mpg with the Defenders won't mean much of a $ hit. Having relatively new tires will help when we sell the Prius.

 

I have one of these:
Pretty cool, and inexpensive, digital instant temperature gauge.

In an attempt to determine if any of the brakes on my Gen II were dragging I've kept the digital tool in the car. After a couple of drives I quickly exited the car and checked the temperature of the brake discs. All were cool and with in the range of 120 - 140 degrees F. So no dragging brakes.

I do have a dragging brake on my boat trailer. I checked it a few days ago and it read 330 degrees. The wheel was sizzling. I have to replace the brakes on that wheel.

I still have no clue why the mileage on our Prius dropped. Highway miles are fine. It's just the around town slower speeds where we are taking the hit. Many other car owners would be thrilled to be hitting 42-43 mpg. We Prius owners know better.