Hybrid System Failing?

You are right. If there are no warning lights on, then no diagnostic trouble codes are logged. Therefore, from the dealer service department's point of view, nothing is wrong with your car. There really is nothing you can do or say to get around that.

You haven't mentioned tire inflation pressure. I suggest you check all four tires and inflate to 44/42 psi front/rear.

Also, if you are still carrying heavy loads in the car, that clearly is not going to help mpg so you need to take a long drive without any excess weight and see what mpg is logged.

Good luck.

 

Anybody else thinking, drum up the chorus now, that little 12 volt auxiliary battery in the right-rear corner of the trunk? If or when has it been replaced? Maybe 8 years on the factory original? I should have that permalink to the diagnostic procedure memorized by now. Do a search for 12V battery and see if those recommendations don't improve things.

 

It might be any one of several things at this point. I would suggest the OP fill out the questionnaire concerning low mileage and then maybe we might be able to help.

As Patrick pointed out, no codes, and no lights means the Prius is functioning normally, or at least within specified parameters.

Here is the questionnaire. Please copy and paste it into your reply and fill in the answers. Then we might be able to assist better.

- What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations)

- What fuel economy are you expecting and why?

- What are the approximate outside air temps?

- How long are your trips?

- How much of it is city vs. highway? Roughly what's the average speed in overall and and of each segment? Is there a lot of stop and go driving?

- What region/state are you in? (if you haven't set your location in your profile)

- What's the terrain like of your drives? (e.g. flat, gentle hills, steep hills, etc.)

- Is your oil overfilled? (i.e. above the full mark on the dipstick)

How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? (Method Here) Weird stuff happening? MPGs dropping? Test The Battery | PriusChat

Have you had your alignment checked? Any pulling or abnormal tire wear?

- Are you using the factory tires and wheels? If not, please indicate tire make, model and size (e.g. Goodyear Assurance Fuel Max 185/65R15).

- What are your tire pressures?

- Make, model, year, engine and transmission of previous car? (e.g. 08 Honda Civic Si 2.0L 4 cylinder, manual transmission) What did you actually get on the same trips/commute? (Please give us actual numbers, not EPA ratings.)

- How are you trying to drive (e.g. trying to stay in electric only?) and how hard are you braking?

- Are you "warming up" the ICE (internal combustion engine) by letting it idle after powering on?

- Are you driving using D or B mode?

- HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to?

- If reporting a mileage drop, did anything significant change on your car (e.g. accident, hit a curb or big pothole throwing off alignment, oil change/other maintenance/repairs, changed tires or wheels, etc.) or your commute?

 

Here's a few things worth checking out.

1. Check the simple things, your 12V battery health, tire pressures and that your oil isn't overfilled.
See: Weird stuff happening? MPGs dropping? Test The Battery | PriusChat

2. Probably a long shot, but some people have had success against various anomalies with a "brain reset". Disconnecting the battery positive for half an hour and then reconnecting.

3. Check the inverter coolant for circulation. You should be able to see it steadily gurgling away if you look down through the filler hole of the reservoir while it's in ready more.
See my post (#10) here: maintenance and repair in Anchorage AK | PriusChat

4. Check the rear battery fan to make sure it's not clogged with dust.
See my post (#31) here: Fur and dirt causing major battery problems | Page 2 | PriusChat

 

Consider this. In the last month or so the temps here in Texas have dropped considerably. Also the winter gas is now in use.

Furthermore, Texas recently raised the speed limits and you are driving considerably faster as per your statement above.

Based on the information given so far, I don't think you have any problems. Sure your traction battery is beginning to show age. But does that mean the system is failing? No, it simply means that your car is not as strong as was in the past. There are many factors that contribute to this.

75 and 80 MPH with an average load on a Prius could very well contribute to the MPG you are reporting. Maybe a few miles more, but with the cold temps we have been having what you are getting is acceptable.

Try slowing down, pump the tires up to 42 F, 40 R and block the grill. Remember the Prius has a load limit of 800 lbs. That includes the driver and any passengers.

Just because the limit is 75 doesn't mean you have to drive that fast. I am still driving 62 to 65 in the 75 zones. I stay in the right hand lane with the other's who are doing the same and let the speed demons pass on the left. I am getting a lot better MPG that way rather than driving 75 to 80. I tried that and saw the MPG drop like a rock.

 

A shorted cell in the 12V battery can cause your issues. If the battery is not able to reach full charge, then the little converter portion of the inverter will work over time to try and charge it. This causes overheating in the inverter and excessive reliance on the ICE.

What happens when you come to a stop? ICE shuts off promptly? When you are cruising in a hilly area, does the car go in and out of EV mode frequently? My guess is that your ICE is running continuously.

If you were to run Priidash or Torque and look at the various temperatures in the system, I'm sure the problem would be apparent.

 

Don't accept it. My last two non-hybrids displayed improved MPG with age (to 235k and 175k miles), though that probably had more to do with the adjustment of the nut behind the wheel than to anything else.

 

My point exactly - adjustment of the nut behind the wheel. Thank you for saying that!

 

I am going to ask the op one more time to please fill out the questionnaire posted above. It would be helpful in more ways than one.

In another part of the forum it is stated that it is a requirement of users with less than 50 post's when complaining about fuel economy.

The following is copied directly from the source page where the questionnaire above came from.

In the interests of being able to more efficiently answer common requests for fuel economy help (e.g. "help, I'm getting only 35 mpg", "I'm very disappointed w/the mileage of my Prius", etc.), please copy and paste the questions below then do your best to answer most of the questions below in your post.

This is required of users w/less than 50 posts. Many Priuschat members are eager to help give suggestions, tell you that your mileage is normal/abnormal, etc, but often, we don't have enough information and are left guessing, wasting time posting guesses or the same questions/responses, etc.


Read more: http://priuschat.com/threads/fuel-economy-complaints-queries-please-copy-paste-answer-these-questions-esp-if-youre-new.77075/#ixzz2qdS07ORS
Follow us: @PriusChat on Twitter | PriusChat on Facebook

 

It would help to know what the tires are that are on your Prius now. IE: Size and brand.

Also it would help if you were to run the test on the MFD and report all three values. The test run's best if you do it after the Prius has set overnight.

Based on all the info you have provided so far, I think your alignment is part of the problem.

On the subject of the tires. It is given that the tires have been replaced at one point or another. It might also help when giving the data on the tires (size and brand) if you were to add when these tires were mounted and also if they were new at the time of purchase.

The Prius is a economical vehicle, but it also will vary in that aspect to a lot of variables. As I stated earlier, I think you have more than one problem that is contributing to your loss. But nailing it down is going to be the trick.

Thank you for taking the time to fill out the questionnaire.

 

Watched the video. To me, nothing looks amiss for a typical incline @ 70 MPH.

I note it was night time. I saw it was 57 outside but have no idea what the climate control was set on.

I realize you have touched on this in your reply to the questionnaire, but that data does effect MPG.

It would be nice if you were to post the information requested above concerning the brand, model and size of all four tires and the exact pressures on the front and back when measured while the tires are cold.

You may be discounting the alignment of your Prius also. It doesn't take much to cause the Prius to suffer in the MPG world and alignments are critical if you want good MPG.

Also concerning the tires. They do make a BIG difference in how the Prius performs both in handling and MPG. That is why the data is asked for.

It is possible that the modules in your traction battery are not holding as much charge as they used to when they were new. But until the car actually codes and the red triangle or CEL light comes on, there is no mechanic in the world that is going to tell you there is something wrong with your car. They can speculate, but without a DTC code present the car is operating "normally".

This has been mentioned before also. The 12 volt battery could be weak. The test is readily available onboard and the technique is above. Still haven't heard what the results are. It only takes a few seconds to run this test first thing in the morning before you set off. Please take the time to run the test and post all three values. The technique is plainly spelled out below.

DO-IT-YOURSELF TEST PROCEDURE (thanks to jdenenberg):
- Without brake pedal, press the Power button once and release to enter ACC mode
- Press and hold the MFD Info button, then turn the headlights on and off three times to enter Maintenance mode; release Info button
- Press “Menu” (on screen)
- Press “Display Check”
- Press “Vehicle Signal Check” - the battery voltage is shown and should be about 12.4 to 12.8 Volts (normal for an unloaded battery)
- Again without brake pedal, press Power button and release to put a current load on the battery - the voltage should stay above 12.0V (if less than 12.0V the battery is not well, or there is a fault or unusual load somewhere)
- Press brake pedal and press Power button once to enter "Ready" mode - the battery is now charging at about 14V (if less than 13.6V or more than 14.4 there may be a problem with the charging circuit)
- Turn car OFF to leave Maintenance mode

So far with all the data you have provided, it is my opinion that your car needs an alignment and could be running non LRR type tires.

 

Sounds like some good advice above.

Just thought I would add in some comments, as someone who has had the HV battery fail on my 2006 Prius at about 171K miles (well beyond warranty, unfortunately...).

It happened in May 2013, and the first symptom was that the battery charging and discharging became very erratic. I.e. the battery charge would go from one extreme to the other (full green to 1 bar pink and back), in a matter of 1-2 minutes, all while rolling at consistent speed on flat ground (!). After driving the car 7 years, I definitely recognized the change, but curiously the car was also getting amazing fuel economy (better than usual) at the same time, at least according to the MFD.

It was about 2 weeks after this behaviour started that the dash suddenly lit up like a Christmas tree, indicating "Problem" across the top of the MFD.

Fortunately, the Prius is engineered not to strand you, and you will still be mobile, though likely with reduced power. The battery fan will also blow continuously as well. Sometimes the car would drive 'normally', while other times the engine would race and you would have virtually no power, essentially feeling like you are trying to accelerate in 2nd gear from a stop with a manual transmission. I would have to pull over and 'reboot' the car to get out of this mode. Had to do this more frequently with each passing day, until I parked the car and got around with my wife's Kia until I found a solution.

Anyway, to make a long story short, I solicited three different dealers who only offered a full HV battery replacement ($3K+) as a solution, all claiming Toyota did not provide part numbers for replacing individual cells. I did find an independent guy through re-involt.com here in Toronto, Ontario, who was able to rebuild my battery (4 cells of 28 needed replacement) for less than half the cost, also guaranteeing his work for 1 year, and so far so good, 17K miles later. I would be more than happy to relay his info for anyone in the area.

My mechanic did warn me that it is ok to drive a short time in this condition, but that it should be addressed ASAP, as the failing battery cell could overheat and explode, which WOULD cripple the car and kill expensive ECU computers. That's not good.

In any case, just thought I would share some of my experience here so you will recognize it if your '05 takes a turn for the worse, as the age is getting up there...

Good luck!

 

Hi Kevin, unfortunately, I think my battery is dying...currently at the dealers for diagnostics but symptoms seem to point to a dead battery. Could you please send me your contact? Thanks much!