Latest Software Update Safety Recall Resulting in 8mpg less...

Excellent mpg! I found my actual to be between 1.5 to 2 mpg less than the computer indication on my 2010 since new!

 

Prius went in to the dealer 0n August 18th with mileage complaint. Dealer said they put the scanner on and no error codes. I asked if they drove the vehicle to verify mileage claim and they said there are no TSB's which define how to treat low mpg claims from owners. The service manager wrote the 800 number for Toyota Customer Service on the top of the invoice. I spent 15 minutes on the phone providing the information only to have the woman ask "What do you want us to do? The AGG21A software update skid control service was performed on 4/16/14 and since that time the vehicle has consistently gotten 36-38 MPG as measured by miles driven divided by gallons to fill. I was told by the customer service rep there are no other customers with this issue. Please call the number at 800-331-4331 and voice your issues with reduced mileage after the software update. Waited a month and did not even get a response from Toyota. I like the idea of filing a complaint with the government agencies. Probably the only way to make Toyota responsible for their mistakes. Started telling people not to buy a Prius. This may be my last Toyota if they don't address the problem soon.

 

My recall notices id's the work as "software update to the Motor/Generator ECU and Power Management ECU, within hybrid invertor assembly". Is that what you're referring to?

There have been several reports here: people getting good mileage, get the recall, mileage goes down, go back and have the recall re-applied, mileage goes back up. As if something can mess up in the application of the update, and a redo can remedy it. Maybe you can ask them to re-apply the update?

FYI, we've had the update, and no drop in mpg.

 

Los Angeles area, warm temps, 5-6 tanks of gas and 60% local driving, Scan Gauge equipped.

I defiantly see about a 6mpg reduction after the update. We all know that the gas engine runs more but I also see wacky things like the gas engine charging the battery on flat local roads when the SOC is at 66-67% (warm engine). I see frequent times when the car won't tap into the battery, slower flat local roads. BEFORE the update the car always quickly bring the SOC back to 60%, it was very good about that. Now I have frequent times when I return home with 66-67% SOC. I don't quickly come to stops filling battery. Its frustrating seeing 45/47mpg avg per tank when I used to see 51/53 mpg. Its is better then 22 avg of my last car but I am not seeing the 52 that I used to see.

Life goes on.....

 

I think that is a little extreme of a measure IMHO. A lot of us have had the software update with no impact on mpg. The only reasonable explanation is the update needs to be redone or there is something else wrong with the car. Toyota makes a fine automobile and reliability is unsurpassed especially in a prius.

 

A lot of you say the Update would need to be redone, implying that the initial deployment could be corrupt. Wouldn't that trigger all kinds of red flags, CEL, Check Hybrid System, et cetera et cetera?

 

There are others including the hypothesis that the MPG effects are in a narrow vehicle power range. Driving styles and profiles vary and it is possible those who have to frequently use 'floor the accelerator' may suffer a greater loss than those who do not have to use maximum acceleration frequently. But this is not the only alternative.

One could rent a Prius for a week and compare the rental MPG versus the owner's Prius performance. If they are identical, the problem is not unique to one vehicle.

Bob Wilson

 

Not always no. The computer is just compensating to the new software. If the update didn't go well it will run but you would notice a decline in mpg. Multiple systems have to be updated and it is possible that one went well and others didn't. That's why re flashing might solve the problem

 

I have two Priuses and both got the update. My wife's works as it did and mine lost 5-8 MPG. We have tried swapping cars, and the loss stays with the car, where we both get the better millage in her car, and the less in mine. It is the car since the recall, and was easy to see that it happened that day with the computer calculated MPG, which is right there on the dash to see. No other changes occurred. I have been told that if the re-flash upgrade didn't would the computer would tell them, so Toyota claims that is not the issue (or that there is an issue at all). I also do not hit the accelerator hard and try to get the best millage possible.

 

Ok, now we have a chance to figure out what is going on. Would you be willing to run a data recording, OBD scanner and GPS mouse with each car and share the data with me?

What I propose is first normalizing the two cars, tire pressure and alignment along with transaxle oil change. Then gathering engine and transmission temperature, engine power, fuel consumption, speed, and altitude. To keep the 'route' anonymous, we'll offset the longitude and latitude so 'home' is in the middle of the Atlantic on the equator (we don't want to provide a map to your home and business.)

I'll provide the instrumentation; you'll provide the test cars and cases and share the data with me, and; we'll negotiate 'normalizing' the cars. However, I would like to see the results of a cruise control managed benchmark for both cars before the instrumented test.

PRETEST QUALIFICATION BENCHMARK

I don't see your profile location so I can't use Google Map to suggest some benchmark tracks. This is what I do:

• First look for a 'beltway loop' over relatively flat terrain. Not always possible but a loop without stop lights or stop signs is the ideal track because once on cruise control, the car can do a full loop with little expectation of stop-start or speed changes.
• Next look at roads near rivers as these are often relatively flat areas and often have stretches with no lights or stop signs. You're looking for ~10 mile stretches where cruise control manages the speed and the car can turn around and repeat the second pass in the opposite direction. Google street view is great way to check the route out early.
• Finally, look for roads in farm areas. Try to find stretches where there are no lights or stop signs so the car can run ~10 miles on cruise control and then do the second pass over the same route.

What we want to do is test both cars, above 50 mph and under 40 mph, the engine-always and hybrid mode speeds, and see if the mileage impact follows the car. Of course, make sure both cars have identical tire pressure and the temperatures are within ~10F. Dry, of course.

These two initial data points allow us to see if ordinary, cruise control operated, Prius can demonstrate the reported MPG problem. If it does, life becomes a lot simpler as this can be used by anyone and we only have to document the problem with OBD and GPS data. If not, we'll have to use the advanced data recording mechanism to diagnose what is going on in your particular driving routes. The initial benchmarks can be run at anytime but tt will take me a couple of months to get the test rig together.

I'll have to use a 'cheap' OBD interface and Y-cable and miniVCI to reverse engineer the strings needed for these metrics. "Frank" has done something like this but I really don't know if I can replicate his instrumentation that appears to be Android based. Regardless, once the OBD commands and responses are found, the rest is a simple software and integration problem.

So what do you thing? Would you like to participate in shooting this problem? It won't be fast, I have other commitments, but it would be interesting.

Bob Wilson

 

I live in San Diego, I could do the measurements, but I am not sure what will be found. The dealer agrees that I am getting less, but since their diagnostics don't show anything, they say it has to be something other than the car. They are also now discounting any of my measurements, since I got new tires, even though it was months later, and after I had already complained about the mileage problem. So my wife and I do have different tires at this point, so they will not take any comparisons, because there is currently something different.

 

In a pinch you could swap the tires.

I really hope Toyota doesn't pull a "Honda" on this. You know, as in: "Bring we the broomstick of the witch of the west, then we can talk...".

 

Perhaps if you could check the trip meter distance versus mile-markers or GPS recorded distance for both cars?

Bob Wilson

 

Oh, I thought the issue with the different tires was rolling resistance, ie: with the Prius with lower mpg, they were trying to pin it on tire RR. Not different OD's.

 

There can be significant differences in revs/mile that throw off the true MPG, speed, and distance. By design, I'm running tires 6.52% over-sized on our 2003 Prius to in effect add an 'over drive' gear to my Prius. It is just another one of my experiments. But I noticed two common reports:

• new tire MPG hit - this makes sense as larger diameter from the new tread will have this symptom . . . MPG will appear to go down. As the tires wear, the apparent MPG will increase. It is a Geometry thang.
• inconsistent LRR MPG reports - it is as if some unexplained variable is involved . . . revs/mile is seldom cited

The only way to really know is to run the car over a measured distance with mile markers or a GPS record of distance traveled with a reset trip meter.

Bob Wilson

 

Larry, have you done the ECU reset like we told you over a month ago?

 

Can you please explain this a little bit more? As far as the car is concerned, it's the revs/mile programmed into the computer (so constant) and the energy used to make those revs that it bases its MPG calculation on correct? So, that leaves only the energy used to make those preset number of revolutions as a variable, right? So, it takes more energy to move a larger diameter tire of the same make/model than a smaller one, but then the car ends up traveling more distance in the same number of revolutions with the larger diameter tire. Do I understand correctly that the new tire MPG hit is because of this extra energy having to be expended to move the larger diameter (so heavier) tire? TIA.

 

And now for a joke....

Yo' mamma's so fat that SHE is why her Prius got 8 mpg less after Toyota did the recall.

 

Actually the fuel consumed over a given distance for those who do MPG. Invert the ratio for metric units.

Actually it is the "revs/mile" of the tires that change. New, the deep tread depth means the car travels further for every wheel rotation and later a shorter true distance when the tread is worn off. But the computer constant for "revs/mile" does not tract the true tread depth throwing off the calculation of MPG, speedometer and trip meter. That is why it is important to benchmark the trip meter distance versus mile marker or GPS.

Although the tire mass has an effect, it is tiny, 0.1 lbs/3200 lbs ~= .0031%, compared to the effect of tire diameter or more accurately, the revs/mile. With our old Sumitomos, they started out with ~6% over size and ended up 5% over size, an honest 1% difference. Also, the tire treads are the part that flexes the most and thus loses energy.

A new tire has much thicker tread, a larger rubber mass, that flexes every time it comes in contact with the road and then straightens upon leaving the road. This flexing of tread tire mass is the largest loss of energy in new tires. So a new tire starts at 11/32 tread depth but becomes illegal at 2/32. For illustrative purposes, assume the casing is 8/32 deep:

• 11 + 8 = 19/32 # New tire tread and casing over contact area
  
• 2 + 8 = 10/32 # Worn tire, end of life
• (19 - 10) / 19 ~= 47% loss of tread and pavement contacting, flexing material

Now higher tire pressure reduces the contact area and subsequent amount of tread and casing that has to flex. Higher pressure, less material flexes on each rotation. This is why higher tire pressures are desirable for lowest rolling resistance.

There is an old racing car technique called "shaving the tires" where a team carefully cuts off the excess tread of the tires before a race. As long as 3/32 is on what remains, they are 'legal' but gain the lower rolling resistance from a thinner tread.

Please understand these are basic tire physics and have nothing to do with the tire rubber characteristics and layup. Low Rolling Resistance tires play in this area and then the vendors don't trust us with the real metrics. <gerrrrrr!!!>

Bob Wilson

 

First off, I wouldn't touch the car's mpg calculation, it's wildly optimistic, likely by design.

To calculate mpg with stock tire setup, you need the distance travelled (simplest method is to just use the odometer, or trip meter). There's minor errors in that value, if the stock tire is new, vs worn, due to the slight reduction in diameter. But these are crumbs: if the odometer was grossly in error, Toyota would be having lawsuits.

You also need the amount of gas consumed. If you fill up the same way, every tank, say stop when the pump's auto shut-off stops, you're going to get fairly consistant, accurate value.

Now, if you go to a non-stock tire size, say markedly bigger outside diameter, you are going to confuse the car. It doesn't know, it's just counting tire revolutions and basing the odometer display on that. In fact you will have travelled further than the odometer reports. And this will screw up your mpg calculation.

But with stock tires (new or worn), and consistant fill-up procedure, the variations are very minor.