05 MPG down to 35...what's wrong?

Car: 2005 Prius with all options purchased in Jan 2005
Mileage: 47,000
Location: Southern Florida
All service and oil changes have been performed per the manual.
It's under a Toyota Preferred Car Platinum Warranty (7 year/75,000)

Until recently my Prius averaged between 43 and 45 MPG. The only problem I've had with the vehicle are a dead battery and two burnt out lamps. It has been the best car from a reliability standpoint that I have ever owned.

About two months ago I noticed that my gas mileage was dropping into the high 30s (I had never had a tank average under 40 including running all day at 70+ MPH). Nothing about my daily drives had changed.

So, I checked my air pressure (I keep my tires around 38 psi) and all was well. Over the next few weeks I tried switching brands of gas and my MPG continued to drop into the mid 30s. I had an appointment to get the gas pedal recall fixed at Delray Toyota and told them to check about the mileage. They reported there was nothing wrong with the car and said it was probably caused by the ethanol in the gas.

We were away for a couple of weeks and when I came back I was driving on a highway and felt a huge power drop and all of the warning lights (Check Engine), etc lit up. I was close to another dealer and brought it in.

They diagnosed that a water pump for the hybrid system had failed and replaced it under my extended warranty.

I am on my first tank of gas since leaving the dealer and my MPG is still sitting around 36 or so. When I watch the Info display I notice that the car is barely running off the battery...even at low speeds. I used to be able to drive on battery at 38 for a couple of miles by feathering the gas pedal...that's no longer possible.

The car still appears to be driving alright, although it feels a tiny bit "rougher" at times. Engine power seems the same as always, but MPG is way too low.

Anyone have any ideas of what the problem might be and how I can get a Toyota dealer or Toyota to diagnose and fix the issue?

Thanks in advance for your help and suggestions.

 

It is the second battery in the car (the first was replaced by Toyota after about a year when it was dead), but I did have to jump it (using one of those external batteries..not another car) a while back after a light was left on and I found the battery dead. The car hasn't had any problem starting since then, but I will give it a test this morning. Thank you for the suggestion. I'll report back.

 

Okay, here's what happened.

Got in the car...pressed button one time. Only the Start button, Nav display and radio lights lit up. The main headlights (which are always on), and dashboard lights did not come on. The Nav display was on the power screen and showed the battery completely empty. The windows did not work.

I then hit Start again and everything lit up as normal. Fan started, headlights on, etc. etc., the power indicator now showed normal too...with about a 3/4 charge on the main battery. The windows worked and seemed to be at normal speed.

I pressed the brake, hit Start and the car started.

I shut it down and opened the door to kill the headlights, etc.

Same sequence again...same results.

I don't recall a single press after bringing the car into a mode where only the Nav came on, but I also can't remember the last time I pressed start without starting the car.

 

Jimbo,

Thank you for the information and link. I ran the test and everything was well within the parameters the other posters had given. I'm not adverse to nuking a new battery i'm just not sure that's the issue here.

It seems to me that the main battery is discharging much faster than it did in the past. It will go from eight bars (just under green) to two or three bars when I sit and idle in about a minute...now this is South Florida so the A/C is always working (thermostat setting at 77).

Is there a way to test the hybrid battery to see if it's healthy?

Thanks again for the suggestions.

...ken

 

Jimbo,

Let me just clarify. When I tested this morning (it had been sitting in the garage all night).

1. I get in car (headlight switch was in the On position). I press Start without the brake and the only thing that lights up is the MFD and the CD changer lights. The headlights did not come on and the windows didn't work. Now, I didn't try cycling the lights off and on...so that might have come on if I did that.

2. Second press of Start (without brake) and everything lights up normally and the headlights come on....windows work, etc. etc.

3. Press Start again and car shuts down except the headlights and dome light stay on until after I open the driver's side door.

4. Press Start again with brake and car starts.

The second group of tests I did (the ones with the car's display) after driving for awhile.

I'm going to buy a new battery and see what happens, as you said it's not like I haven't gotten my money's worth out of the existing battery.

Hopefully, that will correct the issue and I'll be back to getting ~45 mpg again. I drove about 50 miles today...the type of driving where I used to get over 50MPG (averaging around 40 mph) and it was 35.6. Something's not right.

Anyway, if anyone else has any ideas let me know. I'll report back after getting the battery. I'll probably try the 3rd party vendor in this thread.

 

I received the replacement battery on Thursday, but unfortunately, a piece of the installation kit was missing. They sent a replacement out so I should have it in next week.

On a related note...Toyota really needs to make some things user serviceable. Changing items like lights and now a battery shouldn't require adapter kits or five single-spaced pages of instructions. I'm not saying it will be hard to do...it's just a lot harder than it needs to be.

 

Jim,

You're correct...I purchased from the 3rd party listed at the beginning of the thread. I have no doubt that Toyota isn't the only company to make servicing basic parts hard...it's just a shame that changing a side marker lamp goes from a $3 expense to costing $60 at a dealer because of the complexity.
My dealer wanted over $250 to change the battery.

 

Well...new battery is in. The old battery tested as good, but it did have around four years on it so I don't feel bad about that. What does have me worried is the continued low MPG. For 46,000 miles I always averaged between 42 and 45 mpg. In the same driving situation the car is now getting somewhere around 34mpg.
Tires are about a year old and are inflated to roughly 38psi.
Oil has been changed regularly by my dealer.
Two dealers and a private mechanic tell me there are no trouble codes.
My driving habits haven't changed nor has where or when I'm driving.
The car seems to be driving okay.
Obviously something is wrong....and I'd prefer not to be on a trip when it fails completely.
So....any ideas?