Main Battery light flashed briefly while braking when exiting highway in neutral.

My 2008 Prius (~130k mi) MAIN BATT light flashed briefly last night (barely half a second- long enough for me to hear a few strange beeps and see the red main battery triangle flash and go right back off) just as I was getting off the highway with the car in neutral and performing a firm hard stop from high speed to try to bed the new rear brake shoes/drums that were just replaced.

The rear wheel cylinders were also replaced and the brakes feel a bit "off" now whereas before they were very firm and almost a bit too grabby, especially at slow speed stops- I found this to be a symptom of abnormally wet weather (which we have been having this winter in the Bay Area of California) based on my research so far.

I found that strange considering I drive it between 80mph and 100mph like a race car regularly and figured the brakes get worked out pretty aggressively in a day to day basis when I'm at the wheel- but I guess overnight is enough time for a thin layer of oxidation to work it's magic and make my slow speed stops harsh and abrupt?

I haven't driven it enough yet to decide if it's just the rear shoes that haven't fully seated/burned off their residues yet or if I may have a small pocket of air trapped that needs to be bled out. I did a small one-man bleed on each side just enough to fill the wheel cylinders, barely any loss of total fluid amount and no abnormal codes or warnings have been set since replacing my rear brakes two days ago- I was very careful with my procedure.

Any idea the relation here?

I checked my 12v battery and it was at 12.23V as of this morning and dropped to around 11.5V when loaded with headlights and brake lights with the accessories added. I know a bad 12v can throw all sorts of weird stuff around but I thought my 12v was good until it starts dipping into the 10V range?

I will update as I get more driving in. I usually drive it 90 miles round trip every morning taking my wife to work in SF.

Thanks!

-Mark

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Yes I saw the words "MAIN BATT" inside a small red triangle in top left corner of the center (MFD?) display screen.

Also, I just noticed that now when I put my foot on the brake with car in drive (like I'm waiting at a stop light) that the battery is sending power to the electric motor and from there to the front wheels. No matter how hard I press on the brake pedal it wont stop the power flow. Before I changed the brakes it would do something similar where it would continue sending power (according to MFD) to the front wheels until I stepped on my brake pedal a little bit harder and that would always stop the power flow.

My check engine light has been on for months because I kept getting random EVAP SYSTEM codes suggesting that my fuel tank's check valve was stuck.

Let it be noted also that last night when the main battery signal flashed I had only 1 bar on my traction battery in the MFD at that moment. I regularly see the HV traction battery dip to the bottom 1 or 2 bars fwiw.

Also to note we have the dead dashboard problem so more often than not I have zero to minimal lights on my dash (besides check engine or maintenance required lights).

I picked up a Tech Stream scan tool to be used with my laptop but I have not finished setting it all up. If anyone has some helpful tips or pointers regarding that I am open to suggestions.

I will post the picture I'm talking about of the power going to the front wheels while stopped fully at a light in drive.



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Mendel I hear what you are saying but I'm not really a guy who goes by the owners manual. That information is generic at best and not always best practice, but easiest/simplest practice for most people who aren't very technical. This is all my opinion of course, to each their own.

Bisco, I am in California which is a 10/150 state afaik. I would not doubt having a bad cell or few with the way I drive- I know it's just part of the deal. Also we purchased this car used with about 70,000 mi. I have changed the spark plugs, several air filters, oil and filters of course, changed the transmission fluid, front brake pads and rotors, rear wheel cylinders, drums, and shoes, cleaned MAF, throttle body, intake, PCV valve, cleaned the battery cooling fan, etc. I am new here but certainly not new to mechanics or troubleshooting. I drive my vehicles hard- to their limits- but I am religious about high quality maintenance.

I am curious if I can still get the traction battery replaced if 1.) I am not the original owner, 2.) my dash combo meter is blacked out (and not counting miles afaik) 90% of the time- today was a rare exception it came on! And 3.) how bad does the traction battery have to be to get official Toyota-sponsored replacement?

Augustus88, I completely agree with your theory- it makes sense since I normally don't use neutral gear often, but I definitely use B for engine braking daily typically. It turns out, despite my being careful as possible when doing the brakes Monday, that it did in fact set the ABS and ! inside a circle symbols on my dash! I didn't know this until my dash decided to randomly work this morning, thankfully. I promptly performed the 4/13 pin paperclip reset special on the OBDII port and reset the braking system before driving my 40ish miles home. Immediately I could tell the braking felt different (the rear brakes were finally grabbing properly along with the fronts) as the rear didnt lift and then settle when coming to a complete stop. 40+ miles later, no brake system warning lights have come on, brakes feel 100% on point now, and best of all that weird 'not stopping power to the front wheels' stopped when I cleared the brake system warnings.

Finally, yes I understand the brake bedding procedures and properly burned in my front rotors and pads when I replaced them months ago per the manufacturer's recommendations (not the owner's manual guidelines). I can 100% say proper burn in is essential in performance type pads. The front pads I put on from RockAuto are these:

POWER STOP Z23822

And I can honestly say they are some of the nicest front brake combos I have used- highly recommended.

 

Last time I brought our Prius to our local stealership regarding our dead dash they basically told me I will need to leave it with them to diagnose and IF they determine it is the combo meter fault it should get replaced in a few days time, etc on Toyota's dime. BUT if it's "not" I'm on the hook for their BS $100+ diagnostic fees and then some depending what BS they think they can try to fool me with. I tried explaining to them I have thoroughly read up on the issue (that they try to pass as not an issue at all) and knew it was a faulty combo meter dash display unit, but they insisted other things cause similar behavior. If I recall correctly in my brief exchange with them that morning they suggested it was likely my 12V battery (which at the time it was NOT, but I know it's end is near now and we don't even have the extra money for me to replace it myself), let alone get screwed for several hundred from Toyota. Bottom line is I don't trust them, their service people, or mechanics to not get screwed financially. If anyone knows of a 'reputable' Toyota dealer in the Bay Area that is cool about making this repair I will gladly bring it there.

 

Honestly, that's kind of been my goal to an extent. lol

 

I will say it definitely has less pulling power when the HV battery is low- like it struggles in the 90's to catch 100, but when my bars are in the blue range it seems to pull to 100+ considerably easier.

 

Surprisingly I manage to average about 32 mpg with aggressive commuting. When I drive it "all out" it dips below 30's sometimes.

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Great info here, thanks a ton! I will attempt the Toyota dealer battle first to see if we can get it done on the books, but it's funny you ask about my electronics level of skill because I used to be an appliance repair tech full time. I am also going to school for Mechatronic Engineering so that's absolutely right up my alley of interest and skill.

When I looked into this in the past, logistics issues and finances were our primary discouragement since we are pretty reliant on this car since moving to the edge of the bay and having a baby.

Do you know if they base this off of the vehicle year or does it go by months? I'm pretty sure our 2008 is right down to the line in terms of the time frames specified for replacements allowed.

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