Mileage Going Down

I could be that the HV battery is having trouble. That would explain both the loss of mileage and the loss of regenerative capacity.

Tom

 

It is time to see the dealer -- before you get too close to your 100,000 mile mark. If it is a battery issue, then have it diagnosed as such so you are covered by the original warranty.

 

Reformulated fuel would account for some or all of the change. In other words, if your gas was switched to E10, there's nothing the dealer can do for you.

At some point, you'll want to have the transaxle fluid changed. That may provide a minor restore back to performance when the car was younger.

And I too (now at 103,600 miles) have seen a difference in re/charging with age. But that appears to just be an indicator of not being new, nothing to actually worry about.

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Please keep us posted.

 

Hi John,

I agree that it is a good idea to have the transaxle fluid changed periodically for the sake of encouraging transaxle longevity. However, I don't think that a fluid change will address the mpg decline that the OP noted. New fluid has greater viscosity; hence the transaxle will have slightly more drag with new fluid.

 

I agree that this sounds like a traction battery issue. With your route the traction battery is being cycled from as full as the hybrid control system will let it charge to about as low as it will let it get on a daily basis. (The B mode part, even when new is the tip off that the route is putting the maximum stress on the battery.) This would be expected to result in earlier battery failure than a flatter route that didn't push the battery to the edges of the envelope. With the standard (non-CA) warranty at 100,000 miles it looks like Toyota had a reasonable idea of what the lifetime would be in a high stress situation for the battery.

This is great news for you in some ways. Since it is still in warranty you should get a brand new battery near the end of the warranty, plus there is usually some sort of add on time for the new part. And your car is still driveable until the new battery arrives. (Buy a lotto ticket, today!)

It gets better...even if the dealer concludes it is not the battery and the battery then fails sometime after 100,000 miles (say within a year of your dealer visit) then you will still have documentation of the problem--make sure the symptoms are on the service printout. This will prove that the problem existed before the warranty was exceeded and you did your part to have it serviced then. I had a minor, but similar situation with Nissan about 10 years ago with an intermittent engine electrical glitch that the dealer couldn't find within warranty. It went away until just after my powertrain coverage expired, so I had to pay for it on my own dime. I brought in my earlier paperwork to the dealer who was sympathetic and said to write Nissan about it. I wrote the letter to Nissan (praised the dealer in it to make sure they were on my side) explaining why it should be covered and enclosing copies of the service printouts. I would have been happy with 50%, they gave me 100%.

 

No, you are right about B mode. Dealers continue to be a surprisingly poor source of information on the inner workings of the Prius.

If you are used to non-oxygenated fuels in the summer and there are E10 stickers now, then I would blame at least part of it on the booze. The battery is certainly aging after almost 100k in hilly terrain but that doesn't mean it's on its way out. I also am not surprised that they found nothing, since the usual protocol is to stick the scan tool in the port and look for a code. The battery won't set a code until it's really dead.

 

Yep! Hello E10! Thanks to PC and what I learned w/SGII I had increased our MPG ~2-3 MPG on or 2000 Avalon. That's ~10% for us. Then along came E10. Back to were we started. I guess I should be happy though. If we hadn't fine tuned our driving habits, run our psi up to 42/40 and switched to Mobil1, we'd probably have lost the ~10% mpg instead of breaking even.

 

It would be interesting to get some more details from the dealer if possible. In particular the values of all the individual module pair voltages would be of interest. It seems like these voltages will often start to spread out showing signs of some weakening modules before you get to a full failure. If there are no warning lights, the scan tool is likely to say the battery is fine since they probably use the same spec limits. If the voltages all seem pretty tight then it probably is just aging of the battery combined with ethanol and not necessarily a problem. If the voltages are spreading out, you might be able to make a case for a replacement. I'm sure someone on here can give you a good range for the voltages, I want to say 0.02V, but I'm probably remembering that wrong.

Interesting about the "B mode" behavior, I've done some pretty good climbs and descents and gotten full greens but never enough to see that mode. Must be the battery getting all the way up to the hard limit (80%?) and burning off power. I do try pretty hard to only use warp stealth (electric only at high speed) any time I need a little boost on the down hill runs even if it means loosing a little speed to use up some battery and capture as much of the regen as possible. I also try and hit the top of a long downhill with as little battery left as possible for the same reason. I'm sure all that is probably old hat if this is your daily drive!

Rob

 

Temperature might very well have played a part in the previous problems. From what others have posted the battery won't charge over a certain temperature. I don't know if it is restricted at other temperatures. I assume that the vent for battery cooliing was not obstructed before? This has been mentioned as a doh! issue for some when they were having battery troubles.

I'm a novice but I've not read anything anywhere that supports their statement about B mode, that's the opposite of what it does. They've got it confused with regen. Dealers often seem lost when talking about engine management issues, it is not their forte.

The devil is in the details here. How did they determine that nothing was wrong? Did they just check that there were no codes or is there a load test? One would think there would be some sort of standardized load test and the voltages of each block of cells would be reported. The Bentley manual is silent on this, unfortunately. You might have to find a more knowledgable dealer that can recommend a proper diagnostic. A factory service manual would be handy about now.

 

Driver-induced B mode won't charge the battery more, though it will charge it faster than D -- to a point. When the battery reaches and slightly exceeds 80% SOC, charging slows down and then stops to avoid overcharging. After that, continued use of B mode will cause MG1 to spin the ICE higher (I've seen it as high as 3000 RPM coming down a mountain) as the car now tries to bleed off some of that charge. So on a route where you know driving in D will get you to that point anyway and you aren't constantly riding the brakes, you might as well leave it in D.

Mt View seems to be suggesting, however, that B mode is occurring spontaneously. This tells me that the battery already has reached 80%+ SOC. The car seems to put itself into B mode in those conditions, once again to bring the charge back down. Several of us report this observation in another recent thread.

I don't know that outside air temperature has anything to do with it, though admittedly I've never been on mountain roads in temperatures lower than about 70F. But I've seen the battery get up to 120F in those temps on a long descent with lots of regeneration. I would guess an ambient temp 20-30 degrees cooler wouldn't matter.

None of this, of course, addresses his original issue. On the one hand, a 2-3 MPG change can be attributed to the effects of many normal variables, some of which have been mentioned. On the other hand, I'm with Shawn in wondering what the dealer did to evaluate it. It could be they only checked for codes and finding none, concluded nothing was wrong. I'll let those better educated verify this, but if I'm not mistaken, a battery won't throw a code until outright failure. I personally wouldn't be too alarmed at such a small change in fuel economy, but it would be nice to know the battery is OK before 100K.

 

Do you mean to say that the dash display actually changes from "D" to "B" all by itself, without you bumping the shift lever? That is a problem to be fixed.

Battery aging must play some role when fuel economy decreases over time. If the dealer really did test *both* batteries and found no problem then it's hard to say. The other stuff is just normal dealer attempt at income maximization. Ignore that and do only what it says in the Scheduled Maintenance Guide (and also, based on results published elsewhere in this forum, maybe change the transmission fluid at 60,000 miles instead of 100,000).

 

It is my inderstanding, that when the battetry reaches it's full(80%) charge level and is no longer used for regen braking, that the CVT will spin the ICE, "B" mode, before using the physical brakes, if needed to maintain or reduce speed. This should not affect MPG though since the injectors should be off, no fuel, just resistance. There is a loss of energy that could not be captured through regen braking, but the loss sould be the same whether the ECU spins the Ice, "B" mode, or uses the physical brakes.

 

You are right. The first time I test drive a Prius, the sales rep told me "B" means Battery Only Mode (EV?! LOL!)

Also when I ask him where is the spare tire, he actually told me is under the car and tried to look for it and show me... What a useless sales rep!