Back for MORE advice....

New tires sometimes drop the mileage for the first few tanks of gas as they run-in.

A headwind of 30 mph is significant. The drag formula includes the term velocity squared. If you drove 70 mph but faced a 100 mph headwind drag on your car would increase significantly which would drop your mileage significantly.

It may be the start of a problem or just a combination of new tires and a significant headwind.

 

Don't just purchase a new battery. Get it load tested at Auto Parts. Free...... what is the tire air pressure? I have 42 front 38 rear...
possible traction battery failure causes poor mpg but that is pretty low miles.

 

That's the BIG Battery Pack in the back that propels the electric motor

 

Honestly I would have never gone back to a dealer that said tire wear was the problem causing brake, traction and abs lights with a buzzing sound. Complete bs trying to sell tires. I would be disappointed if my shade tree mechanic told me something like that much less a dealer. I won't totally repeat my brake booster/actuator point of view, its here: Tire wear trigger code lights? | PriusChat

I will go with my original diagnosis of brake actuator and booster for the Brake, traction, inflation and ABS lights and suggest that the brake booster and actuator controls all of these except the inflation indicator. The buzzing is the repeated attempts of the brake booster to build up pressure so your brake by wire system will work. Realize, again, that the brake booster and actuator is a chronic problem on Gen 3 Prius' but a v is not covered by their special program. Otherwise its about a $4k retail price ($2250 at my dealer) and even then the brake ecu does not throw the specific booster code until a five minute timeout occurs. Yours may well satisfy long before five minutes. Mine never went longer than 15 seconds per cycle. But it was fixed with a replacement booster and actuator.

The inflation indicator could be a tire pressure sensor going out, fairly normal if they have not been replaced.

The 12vdc battery voltage is supplied by the inverter/converter once you are in Ready mode. It will read 14 to 14.5vdc most of the time even if the 12v battery is old and and fit for the scrap bin. If the 12v battery will cause the car to go into Ready you are pretty safe for that drive cycle. Granted a poor 12v battery will run down quick the one time you don't close the hatch 100% and then no Ready mode, maybe no door unlock or hatch open. You can read 12v voltages in realtime on the head unit: Prius v Display Audio Service Menu w Battery Check | PriusChat

You have added a bag of worms with reduced mpg. Noise at startup and idle is likely the brake booster unless its ungodly bad mechanical clashing type of noise. I doubt that or everyone would recognize the issue.

I would not get too carried away with the mpg "yet" with a 30 mph head wind but I would reset it and watch the mpg over the next couple of tanks. If you want to get relieve paranoia you might try a head gasket test kit. See link.

Head gaskets can leak at a very slow rate at first and cause occasional severe knocking or metal to metal sounds at startup when the engine and transaxle can't immediately synchronize. Again, that's a major "for sure" bad noise, not a buzzing created by a brake booster pump struggling to keep up. At some point, a head gasket problem will move the coolant level up or down and eventually blow white smoke out the tail pipe. But there are milder symptoms at first and the car will run. Again, I'd continue to monitor the mpg and coolant level and focus on the brakes. I would say a return to that dealer is in order. Perhaps with a video of the lights and sounds.

 

Great Post..... wish I was that energetic......... more reasons I don't recommend purchasing a Used 3rd gen.... unless you look forward to Big Problems.....

 

The challenge is the scope of your reported problems is widening.
All these things could be related, or not. Some may not even be problems at all.

But when you are talking about various dash light, intermittent.
Noise on start up.
MPG decline.
!2 volt battery-questions.
Then "partial" solutions such as tire replacement and service center assessments
Evaluation becomes like a juggling act, with more and more balls being added and thrown in the air.

I think what you need to do is focus on exactly what you want to find out first.
I think the 12 volt battery is a good starting point, because it's condition should be totally ascertainable.-Have it tested.
Then you can either check it off the list as a potential problem or replace it, and see how that affects other issues.

In the meantime, you are watching your MPG, not on one specific trip, but over the course of multiple fill ups.
You're watching for the return or disappearance of the dash lights.
You can continue to listen for noises on start up.

Have your 12 volt tested. Because despite the price for replacement, you either need it, or not.
If it needs to be replaced, then it's expense is necessary and worth it. It shouldn't be replaced on trial and error, but knowing if it needs to be replaced is something that should be very determinable.

 

Battery at Auto Zone..... $195

 

12 volt battery itself is not that much, and replacement is $0 if you DIY.

I haven't seen your trouble codes posted here yet. When those dash lights come on, it means there are codes to read. Sometimes it look overwhelming because a bunch of dash lights come on at once, but the way the car is built, several of those lights can be controlled by the same ECU (the brake, skid, and ABS lights are) and it's no great surprise when they come on together. Reading the trouble codes will reveal why they came on.

So far, in all of the times I have had those lights come on in any Prius in my family, never once has it meant the actuator or accumulator needed replacing. Can it mean that? Sure. But read the codes. There are a couple hundred possibilities, many of them fairly straightforward.

There is always someone who will tell you it probably means your actuator, the same way if you mention having a headache there is always someone to tell you their cousin had a brain tumor.

 

I personally think it's the Henway. Have heard of it before....

 

I never have, but I'd guess about five pounds.

 

We had had a Stability Control System indication and a wheel speed sensor code thrown. Turned out to be the anti-icing brine that NJ put down on I-95. Cleaned up the connector, sealed it, and the lights and code have never returned.

 

Generally you can still pull historical codes.

It is convenient to have a reader of your own so you can quickly see what's what.

Many of the ECUs in the car have a fallback trick, often discussed on PriusChat, where with a short piece of wire you can make them blink out two-digit versions of their codes on the dash lights. The brake ECU (responsible for the brake, skid, and ABS lights) is definitely one of those. So there's always some information to get even if an actual code reader isn't handy.

 

I believe your 12v battery is bad. ECU runs off the 12v and performs the diagnostics that control the warning lights. Voltage drops when you start the car and the ECU gets say 9v instead of 12v and you get false warning lights. Also, MPG drop can be caused by bad 12v battery because 12v gets charged by the traction battery (thru DC-DC convertor). If the traction battery spends too much juice trying to charge weak 12v battery, it will have less juice for the motor and then your gas mileage drops. Another (less likely) possibility is DC-DC converter is bad and not charging the 12v battery correctly. Both the 12v battery and charging voltage are easily tested as others have said.

 

That's a Big Henway.....