My 2015 Prius mileage fell from 44 to 35 in January, and now it’s averaging 23 mpg. New plugs, air filter. Tires are excellent and properly inflated. Recently all the error codes went off and the dealer said it was a wheel sensor. Replaced that and the error codes went away. But the mileage continues to fall… No lights on the dash. Dealer says too bad…won’t look at it unless an idiot light comes on. Thoughts?
how many miles on her? are you calculating mpg at the pump miles/gallons? has anything changed, new tires, trip length, frequency? how is the 12 volt health? air and cabin filter? does the car gide freely if you put it in neutral at 10mph? any of the wheels warm to the touch after a long drive? brke caliper pins lubed properly?
NGK. Good ones. My friend runs a big garage. His guy looked it over and says the car is fine. He suspected the Hybrid drive. he was shocked the Dealer only works off idiot lights and codes. I’ll try a different dealer service that was friendly and helpful when I called.
Maybe invest in an OBDII bluetooth reader and take a peak to see what the modules are at voltage wise. This particular one is cheap ($13USD at time of writing) and is recommended by Jack aka Dr. Prius. Outside of some hybrid driver components I'm not sure what else would be causing the sharp drop. If plugs are brand name (you said they are), filters are not clogged (they shouldn't be), and wheels rotate freely (no seized calipers here), then I don't know what else would cause this.
The stock plug is SC16HR11 (supersceding SC20HR11). What kinda NGK's, what part number? Where'd you get them? Did anyone pull one of the plugs and check them? When did that plug change happen?
My MPG started dropping after 100k miles. My nephew has same issue with his 2016 Prius. Likely culprit: burned, dirty ATF WS fluid. Why? After change my nephew reports 4 to 5 MPG improvement.
I went to a different dealer who was very helpful. Sold me Denso plugs and a shop guy walked out to my car and cleaned the MAF sensor in about 60 seconds and wouldn’t charge me. Swapped the plugs and mileage is up to 44. So, between a dirty MAF and non-Denso plugs, not sure but that did the trick for me
I had dealer replace plugs and still 33 mpg. Maybe I didn’t clean MAF sensor correctly or something else like bad transmission.
