Mileage dropping each year in '07

What oil, tires, tire pressure, battery volt numbers? Any other changes in behavior like not shutting off at stop lights or the engine otherwise running more often that it use to?

You can check the 12V battery by following the instructions in this thread after setting up overnight or a number of hours.
Weird stuff happening? MPGs dropping? Test The Battery | PriusChat

Tell us all 3 numbers.

 

Non Low Rolling Resistance tires may cause that low a drop, what tires do you have?

 

HI 3DogLady,

In my book the Sacramento area has the very best conditions for high MPG. Throughout the west coast the Prius always seems to do best in the Sacramento area.

What's the car's maintenance schedule? Is it in need?

If there's not been more than oil changes and if you want to save hundreds of dollars: become a student of DIY things to do to bring your car back to its former glory.

Here's a list of things that could be done that will bring everything back to normal. (I'm sure others will have more to add).

Replace 12volt battery
Change spark plugs
Clean throttle body
Clean oxygen sensor
change air filter
change trans fluid
change inverter fluid
use fuel injector cleaner
use 0w-20 synthetic motor oil
Inflate tires a few pound higher then minimum rec.

All of these projects done by a dealer would cost alot of money, but if you can set aside an hour or two and do one or two of 'em at a time you'll not only save hundreds in seeing MPG's go up above 50, but you'll also be more knowledgeable on how to get the best price if major repairs are ever needed.

PS: Study up on how to pulse & glide

 

12v battery.

 

Welcome to Priuschat 3doglady.

This unfortunately is a quite common experience. Non LRR (low rolling resistance) tires can knock over 5MPG off a Prius, especially with the larger tires on the touring model.

Normally a shorter commute will also put a damper on your MPG. Most people always get their worst fuel economy in the first 5 minutes of a trip. If however the short trip is also a much slower trip, and therefore more opportunities for the Prius to "glide", then this can offset the colder engine MPG hit.

You have to be really careful buying tires. Often two tires may have a really similar looking name but be quite different in terms of rolling resistance (sometimes even just a slight, difference like some suffix letters on the name for example). So could you please give us the exact brand/name/model/size of your current tires?

 

Definitely not normal, even for non-LRR tires. Like others have stated, have your 12v battery voltage checked and let us know if the engine will readily shut down when coming to a stop (after the engine is warmed up and the heater/AC is off).

 

+1
You'll start getting worse symptoms than low mpg's as the 12v aux battery gets weaker & weaker. Change it. Do it now!

 

I'd unhook the 12v battery and charge it, then hook it up again, didn't cost you a penny
Now you've re-booted a digital device (prius), have a fully charged battery and can drive 500-1000 miles letting the mpg accumulate to get a good sense of your actual mileage, of course if the 12v won't take a full charge, it's toast.

My '06 seems to not coast properly at times and I've been suspecting the egr valve, picked up a new one, haven't installed it yet, just sayin'

 

I'll tell eveyone my experience regarding gas mileage. I can't believe that simple tires, as long as they are decent, would make such a dramatic change in mileage:

I bought a used 2007 Prius, and was getting about 43 to 44 mpg from day one. I attributed this to not driving in the "Prius" style to get the best possible mileage. But I was happy with this, having a Tundra before, and only getting 16 mpg, so 43 was like a dream. I drove it like this for a few years, and always had the same mpg, replaced tires, normal maintenance, etc. I tried once to increase the mileage by doing all of the things you would do, coast more, accelerate slower, higher pressure in tires, etc., things to the extreme, but the absolute best mileage I could achieve was about 47 mpg, and driving in that manner "drove" me crazy. Then I got a service code, P0420. This can indicate an issue with the catalytic converter.

I have read a lot of things online since then, and there is a lot of wrong information out there. I have read that there are four oxygen sensors. Thare are only two oxygen sensors. There is a front O2 sensor and a back O2 sensor. Front is before and back is after the catalytic converter. The one after the catalytic converter is a true oxygen sensor, and is used to compare it's signal to the front O2 sensor signal to test if the catalytic converter is functioning properly. From what I read, that was supposed to be the only function of the back O2 sensor. From my own experience, the back O2 sensor does more than just test the catalytic converter function. I have since learned that the front O2 sensor is actually more than that, a sort of fuel/air sensor, to signal to the computer that the exhaust stream is too lean or too rich in fuel. Again, I think that the two sensors work in tandem to do a lot more than just determine if the catalytic converter is working properly. I don't know everything that they do, but I do know that these sensors are the biggest influence on how your engine runs. The computer controls your engine by the signals that it gets from these sensors. Other sensors are used also in controlling your engine, but for many years now, the O2 sensors have been the main sensor for fuel/air ratio control and proper running of automobile engines, from any manufacturer.

Not wanting the expense to replace the catalytic converter, I took the cheaper route and just replaced the back O2 sensor. I IMMEDIATELY STARTED GETTING ANYWHERE FROM 49 TO 52 MPG, without changing anything else, and not changing any of my driving habits. The P0420 code also went away for a few months. This tells me that the car uses both of the oxygen sensors to control fuel flow and to set up proper engine running conditions AND to do exhaust gas checks to indicate catalytic converter issues. I am still getting 49 mpg, driving it like I would any other car, and always get above 49 mpg, regardless of how I drive. This experience alone tells me that BOTH exhaust sensors determine how your car will run.

The back O2 sensor is very easy to replace. It costs about $130 dollars at the Toyota dealer, which is close to online prices after the shipping charges. There are instructions everywhere, but the basic steps are: Safely raise the front of your car so that you can crawl under it. I used ramps. Drove onto them, and had easy access. Pull the carpet down from under the dash in the passenger side of your car, towards the passenger seat, and unplug the sensor from it's plug on the side of the center console hump. Some forums say to disconnect your battery before doing this, but I can think of no reason to do disconnect your battery, since nothing can accidently ground out due to the plug from the sensor protecting the terminals, and why would this sensor have ANY power to it when your car is turned off? These is no reason that Toyota would send power to this sensor unless your car is running. After unplugging it from it's connector, push the rubber grommet that is connected about midway down the sensor wires through the firewall, so that the wires can be pushed through the firewall and under the car. Once the wires are pushed through from inside, (so that they don't twist while unscrewing the sensor) unscrew the sensor from the exhaust pipe AFTER the catalytic converter. I had put some liquid wrench on the threads the night before, which probably helped loosen it, since it unscrewed fairly easily, something I have learned over the years not to expect from any exhaust system bolts, but that may not be necessary. There is a clip at the sensor that holds the wires in a direction away from the exhaust and so that they don't point straight down that you will need to remove from your old sensor to place on the new one. Simply pay attention to how it clips on and replace it in the same manner. Screw in the new sensor, and tighten it to the proper torque. I have worked enough on cars to know what is the correct torque. If you removed the old one, tighten the new one to that same torque. It's hard to explain without a manufacturers torque recommendation. If you need that, I'm sure you can find it somewhere online. Push the new wires back through the same hole into the passenger compartment, and push the rubber grommet attached to the new wires back in place so that it seals the firewall opening (it locks in place when the metal of the firewall goes in between the rubber layers properly). Then plug the new connector into the old plug, fold, the carpet back in place, and you are done. There is a chance you will get some engine codes, as others have mentioned, but I did not. Everything simply worked. There is no way for your car to know this sensor has been replaced, it will simply be getting a new signal, which may be differenct from your old, so the car may need to adjust other conditions, but it should simply work. Mine did.

Now for the "since then" part. I drove this way for a few months, and just got the P0420 code again. My car has 123,000 miles. It makes sense that if one sensor was having issues, then the other probably is too, since they are in a very harch exhaust stream for thousands of miles, and since they work in tandem it is probably always a good idea to replace them in tandem. One reaons that I didn't replace the front sensor when replacing the back one is that the front one is a real PAIN IN THE ARSE to replace. It is also more expensive. It was about $206, but then it does more, and it has a small metal heat shield surrounding it, which only adds to the pain to replace it. Unlike the back sensor which you can easily access from under the car, and with any open end wrench that fits it, the front sensor can only be accessed from above, from under the hood, AFTER removing the windshield wipers, wiper cowls, wiper motor, wiper drain pan, and the fuse block that is attached to the wiper draing pan (in the engine compartment, behind the engine air filter, that is between the windshield and the engine bay. The instructions to do this are on other forums, and though it is tedious, it is not hard, and is an excellent opportunity to clean the drain pan (mine was clogged with leaves, dirt, seeds, etc.). This is just the beginning of the "fun" to replace the front O2 sensor. Once you have removed all of the stuff I mention, then you can look down the back of the engine to see the front O2 sensor sticking out of the drivers side of the exhaust pipe. There will be a heat shield on the exhaust pipe that will prevent you from seeing the threaded connection of the O2 sensor to the exhaust pipe, so you will need to feel for it. This will also prevent spraying any liguid wrench to assist in removing the old sensor. If you follow the cable up from the sensor, you will see where it connects to it's plug. I think you will need to be an amatuer contortionist to unplug this, but it seems like it can be done. There is also a plastic clip half way up the wire to hold the wires to a pipe, away from things to damage it. This is as fas as I've gotten so far. I have not replaced this front O2 sensor yet, I have the sensor, but have spent the last week trying to find a tool that will fit between the sensor's heat shield and will be long enough to engage the hex nut that is inside the heat shield. I tried everywhere, Pep Boys, AutoZone, Harbor Freight, Sears Craftsman, all of them had the correct hex nut size (7/8" or 22 mm), but the overall diameter of the socket was too big to fit inside the sensor's attached heat shield. I finally went to the Toyota service department (Toyota conveniently does not sell any of the special tools required to work on their cars) and looked at what they used to remove this front O2 sensor. It was a Blue-Point YA6675B tool. This is a Snap-On part. Good luck trying to find a Snap-On truck. I called my local NAPA store and the guy happened to know a Snap-On dealer and he had the dealer contact me. I ordered the tool, around $47 with shipping, and 4 days to ship from Chicago. This is such a rarely purchased tool that it wasn't in the local warehouse, had to be shipped from the main warehouse. This is also called a "thin wall" or "shielded" (meaing for a shielded O2 sensor, not a shielded tool), or "heated" (agian, heated sensor, not heated tool) or "Toyota or Lexus heated or shielded" oxygen sensor tool. As far as I can tell, Toyota is the only manufacturer that puts a heat shield around their front O2 sensor so that you need to buy this special sized tool to replace it. The tool must have a certain "reach" to engage the hex-nut of the sensor inside the shield, but can't be too long, as it will not fit into the cramped space where the sensor is located. I bought the Blue-point tool and am still awaiting it's arrival. I know that it will work, as I had my new sensor with me at the Toyota dealer and tried theirs. It easily fits into the heat shield and engages the hex nut. I also ordered a complete set of these type sockets from Amazon since their shipping was much faster than Snap-On, and I should have the set of tools today. I paid about $47, with overnight shipping it was $70 for this set on Amazon, including shipping. I couldn't wait, so I paid overnight shipping. This is an OTC 4673 set, which has an assortment of seven different tools for sensors for cars. One of the sockets in this set is described to be for heated and shielded oxygen sensors, so I am hoping it works for Toyota. I will try this tonight, and see what happens. I don't forsee any issues, but I'm sure a lot of great people through history have thought that very thing. Even with the right tool, it's going to be painful to figure out the proper extensions and angles to remove and replace this front sensor.

My opinion: I think that these sensors slowly begin to fail, until they get to the point that your car's computer can't compensate for their degrading signals anymore, and then it sets a fault code. You get used to this, becasue it is such a slow process, and attribute it to the age of the vehicle, which I did, but I think you may get some incredible results by replacing these sensors if you are in similar conditions (high mileage, less than 49 mpg, etc) It makes sense (to me) to replace these in pairs now that I see that they have multiple functions, not just a single, isolated function as some posts seem to indicate, like the back sensor's only purpose is to detect issues with the catalytic converter. It seems that the front sensor helps control the proper fuel/air ratio, but the back MUST also work with that algorithym, otherwise, why would my mileage go from 43/44 to 49/52 by simply replacing the back O2 sensor?

I will be out about $400 to replace both of these sensors, and countless hours of searching the internet for conflicting information, and the absolutely painful hours to find the proper tool needed to replace the front sensor (so irritating that car maufacturers make cars so painful to work on now), but I think in the end I will have a car that is as efficient as new, or possibly better with potentially better sensors being made to replace to old sensors. The approximate 9 mpg more that I am getting will pay for this in a short amount of time, not to mention the car will run the best it can.

If anyone wants any updates, let me know.

Also, a side note while researching if I need to replace my catalytic converter, I don't see any "valve" on my car's catalytic converter. Some posts have mentioned this valve, and that the shaft can rust and prevent it from working properly, which can set the engine code P0420, but I think that valve was only on the first generation prius, not the second, at least I don't see it on my 2007. Walk the minefield of the internet with some caution. There's a lot of good, but also a lot of bad information out there. Overall, I have found the Prius to be pretty straigtforward to work on, ONCE YOU HAVE THE PROPER INFORMATION. That information is very hard to find with the equal amount of bad information. Toyota just makes some things a pain.

Also, replace your PVC valve ($9) while you have your windshield wipers off and everything out of the way. Simply unscrew and screw in the new one (19mm deep socket or open end wrench). It is located under the L-shaped wiring bundle (directly under the elbow of this "L"-shaped bundle), after you remove the three 10mm screws holding it down. I unclipped the spark plug wires from their coils to allow this wire bundle to be lifted higher, out of the way. I think you could replace this valve without removing the wipers, as some other forums have suggested, by just removing those three screws and lifting the wire bundle that routes your spark plug wires, if your only goal is to replace the PVC valve. The valve is cheap. I have replaced my, and it was clogged pretty good. It should rattle easily. It can probably be simply cleaned with something like brake cleaner fluid, but that's a lot of chemical spray to clean a cheap item.

 

Good info. There was some discussion about taking a standard socket and grinding it down to fit:
Oxygen sensor - collar around it?? | Page 2 | PriusChat

Unfortunately the pictures don't show up anymore. Maybe the Forum Admin can look at that.

 

My update:

My OTC tool set arrived and none of them fit the sensor. I debated waiting for the blue point tool but decided to try to grind down the OTC tool enough so that it would fit. I used my bench grinder and slowly ground it down while checking it with the sensor and finally got it to the point that it would work. I made sure not to heat it too much from the friction of grinding.

I had removed the windshield wipers, motor, and cowlings but could not reach the front sensor with any of my extensions from on top. It was difficult to simply unplug the old sensor. You may be able to use a stubby ratchet, but i don't have one. I finally ran the car on my ramps, crawled under it, and was able to loosen the sensor by running my breaker bar, with an extension pipe alongside the exhaust and used the under body of the car as a pry point, was able to break the sensor free. I had sprayed liquid wrench all over the old sensor the night before, which probably helped in getting it free. Remember, a heat shield on the exhaust blocks your view of the sensor, so I was guessing where to spray. This was very difficult to do. If I had it to do again, with what I learned later, I would remove the exhaust to get to it. Seriously. Spray liquid wrench on the spring bolts that hold the exhaust on and remove it to have relatively easy reach to the front sensor. Spring bolts on the back to connect it to the muffler pipes also.

I finished, put the car back together, started it, and everything ran as expected. I was back to getting 49 Mpg, but soon got the P0420 catalytic converter code.

I bought the direct fit catalytic converter on parts Geek for about $290, including shipping. It arrived in two days, but was in three pieces, while the online picture only showed one piece, just like the original Toyota cat and pipes. The box included the front Doughnut gasket, which didn't fit, and one pipe clamp. Just one pipe clamp. The cat came in three pieces. I would like parts geek to explain to me how I would be able to put three pieces I of pipe together with only one clamp. It's just annoying that I had to drive 30 minutes to pick up another clamp that should have been included. I reused my old front gasket and the old back gasket, since it wasn't included either.

It fit OK, but was very difficult to get the spring bolts back in. I had to use a pneumatic driver so that I could push hard enough to compress the springs on the bolts while the air wrench did the turning. Just a tight fit to be under the car while trying to push and turn.

The catalytic converter has been working for about 500 miles now, and I haven't had the P0420 code since. Seems like the partsgeek cat works for me, though I've read reviews I of people having issues. It was only $290, much less than Toyota wanted, and had a 5 year 50K warranty. We will wait to see how it works long term.