Hello! My Prius has been getting lower and lower MPG over the past many months. Right now it is at 28.5MPG for this tank, it has been in the low 30s for the past several tanks of gas. I have driven in heat and cold over the past couple months and it seems to still been getting worse mpg regardless of weather. I would love some advice on where to start figuring out what's wrong and what to do about it. So far I have changed engine and cabin filters, checked hybrid fan, checked tire pressure (all at 40psi), and used the Dr.Prius app to run battery test (said "battery pack has estimated 49.66% capacity left, is in bad condition but will still run"). I also have the torque pro app. Current situation: -No codes -Getting average MPG in low 30s or high 20s -Seems to have less get up and go lately, when accelerating from a stop it seems to skip a beat or take a second to actually go. -Not 100% sure but I think when I accelerate hard, such as merging on the highway, I smell a burning smell. Other issues that may or may not be related to mpg problem: -Car burns a lot of oil, I have to add about 1 quart every 1k miles or every 3-4 tanks of gas. -4 months ago I drained my 12v battery while camping, I used a battery jump pack to jump it and for awhile after I had a flashing TMPS light (which I read could mean a bad 12v), but I ignored it since all seemed to be working well and after a couple weeks the light just went away. I've not had any trouble starting the car since. -I recently had my back breaks replaced because they were squeaking when coming to a stop. After the replacement the squeaking never stopped, and still hasn't. I have done a lot of maintenance on my car since I've had it, including: -Cleaning out EGR system and replacing PCV valve -Replaced spark plugs about 40k miles ago -Cleaned hybrid battery fan -Inverter failed and was replaced under warranty by dealership -both front and back breaks replaced within last year This car is getting old and is a little beat up from camping, so I don't think it's worth dumping a ton of money into, but with the crappy car buying market I'd like to make it last me a bit longer. I'll diy whatever repairs I can but I'm not experienced with mechanics and am getting by on advice here and YouTube videos. Thank you all so much for help!
Couple of things to check 12v Battery Brake Drag Those two on their own can impact your mileage by a bit.
Thank you! Next time I'm in town I'll take it by AutoZone to check the 12v battery. I'll start looking up how to check break drag to see if I can check it myself or if I need to take it somewhere to have it checked.
@Mendel Leisk has a link to brake drag in his signature. Fairly simple to check out if you are comfortable using a jack, wheel chock, and jack stand.
You should find out why the back brakes are still squeaking. Doesn't sound like they did the job correctly. Once a 12v battery is drained, it looses a lot of life. It would cause the inverter to use more power to try to keep it charged and run the 12v system. Which causes the engine to run longer.
I had a brake job done years ago where the shop didn't replace the hardware, or grease the pins. Had quite a few issues from that. Thanks for posting that @ASRDogman I completely glossed over the idea of taking it back. I went right to thinking about the drag, and that would squeak if there is any metal rubbing.
I now have an appointment to have pepboys do a free break check service on Thursday, and I'll get the 12v tested at an AutoZone. I'll update with those results!
I had my 12v battery checked at AutoZone today and they said it's in great condition. They tested it under CA and CCA (not sure what that means but it said it was good both times) I bought some throttle body cleaner and MAF sensor cleaner and I'll clean those tomorrow, as well as I'm getting my breaks checked tomorrow.
fake plugs are a huge issue. if you don't find the problem, that's another thing to check. dealer only.
I just got back from Pep boys and they said they couldn't find anything wrong with my breaks or tires, no drag, but they did spray down my rotors with some kinda spray since they still squeak sometimes and he said they didn't squeak anymore on his test drive. I'm not sure if that has anything to do with the really crappy mpgs though. Still troubleshooting
did you clean the 4 tiny egr ports in the intake manifold? are you running the same tires as when you got better mileage?
I want to second bisco's statement about the intake manifold. These can get clogged and could be causing some issues as well. The smell of fuel, and hesitation without codes might be pointing to egr and/or the intake manifold. There is a diagnosis that you can do at your own risk. If you block off the egr tube at the valve and the issue(s) goes away, it can be isolated down to these two parts.
