Dramatic mpg drop after service

Try raising the back end with the parking brake off, and check how the wheels turn. A slight drag is ok, but with drum brakes should be close to free spinning.

 

this is all too common after dealer service. i hope mendel's advice solves it, all the best!

 

How old is your 12V battery cooldyood?

Besides checking for brake drag also check your 12V battery voltage. I suspect that sometimes the 12V battery gets drained during a service, and with an old battery sometimes they never really come good with just recharging.

 

don't forget tire pressure, they often lower the tire pressure at dealerships and tire pressure matters more at low speeds than high speeds.

It suggest 40 front 38 rear at the least. Consider 42 front 40 rear if you like.

 

Check to see if they overfilled your crankcase. Too much oil will have a negative influence on mileage.

 

But please do update us on your findings as it helps to accumulate this information for the future.

 

The exact thing happened to me this week. Alarming drop in MFD reported MPG immediately after 100K mi service. Spark plugs, tranny service, brake fluid and adjust brakes. I am replacing 12V battery due to age and low readings in the maintenance display. I will also lift the car and check for dragging drum brake. Plus tire pressures. Hopefully will get it sorted.

 

One thing that has not been pointed out in this string. Whenever Toyota works on the brakes, they always disconnect the 12 volt battery. Anytime the battery is disconnected the Prius resets everything. I have noted that temporary drops in mileage can be contributed to the battery disconnection. I saw the exact same thing when I changed our 12 volt battery in January of this year. The mileage dropped on the MFD, and did not return for at least two tank fulls. However, the manual calculations stayed about the same.

There are other items that can contribute to MPG drops also, but they have already been mentioned in this string. (Tire Pressures, Oil Levels, etc.)

 

Thanks. Good to know. I will be replacing my 12V battery this upcoming week, so I guess everything will reset again.

 

^ You can hook up a low amperage trickle charger to the cables before disconnecting the old battery (be careful with polarity) and this will allow you to save settings.

 

If you follow this advice, be certain to insulate both the negative and positive battery cables since they will be energized. You don't want to allow the positive side of the circuit to ground at any time. In doing so, you can blow some expensive components in the Prius.

There is nothing wrong with doing what Mendel suggests, you just need to be a little more careful due to the live circuits.

Ron

 

Alternatively, one could hook up the charger to the jump points under the hood right? Regardless, one has to be careful NOT to let the positive cable at the battery terminal touch the body and such. I would put it in a double layered thick sock as soon as I disconnect it.

 

Any reason to insulate the negative cable as well? Just insulating the positive should be fine, right?

 

As long as the negative and positive never touch together or the positive grounds out, everything will be ok. I suggest insulating both for extra insurance. Over 4K (four thousand) dollars of damage can be caused in a instant if the system is shorted or polarity is reversed. I do understand though why you would think that insulating the positive would be sufficient.

 

When I replaced the brake fluid in my car, the rear brakes seemed to be locked up. I would hope that this is not what is happening with your car, since driving it long distances in this condition would result in overheating of the brake pads and shoes. I had to jumper two pins on the OBD connector to reset the brake system. I don't remember the pins, but I found the information by searching google, probably from one of these forums. It had something to do with the car expecting either a pressure or brake position that changed when I changed the brake fluid. After the reset everything was fine, before the reset, I could still drive, but definitely a feeling of stuck brakes and a lot of drag on the car. It was like the brakes were constantly applied before the reset. I just found this on another forum, and it sounds like the process that I went through to reset my brake system: "An ABS light can not be reset without a OBD2 compliant reader with ABS reset capability. Removing the battery leads will not reset the ABS light either. That said however, there is a way to reset the ABS light on a 2nd gen Prius. Find the can 2 bus link/ OBD2 port under the dash below your right knee.When looking up at it you will find a connector with 2 rows of 8 pins each. Connect a jumper between pin 4 (CG pin) and pin 13 ( TC pin) on the OBD2 connector. Starting at the top row reading from left to right, pin 4 would be the pin 4 pins away from the left on top row. On bottom row pin 13 would be 4 pins from the right on bottom row. Connect the two pins using a small paper clip, then put the car into ready mode. It will start blinking the ABS light on the dash and the touch screen display will not look normal. Press the brake pedal 8 times or more in 5 seconds after turning the car into ready mode. Turn off the car and remove jumper. The ABS light will not be on. This procedure only resets the light, not the underlying problem. If the original fault is not repaired the light will come on again. In my case I did a brake job on the car and the abs light came on because I moved the piston back in the caliper. The abs system detected a pressure difference between wheel cylinders setting the ABS light."