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Toyota Service
Toyota Service, Toyota Expert
Category: Toyota
Satisfied Customers: 4818
Experience:  30+ Yrs of auto experience, Award Winning Svc. Manager; Just Answer Customer's Choice Award Winner
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07 prius sat all winter with a battery tender on it , I

Customer Question

07 prius sat all winter with a battery tender on it , I started it a couple times ,the tender stopped working , the battery went dead , I recently charged the 12v battery , its full , the car won,t start , I disconnected the hybred and 12v battery over night thinking it would clear the computers but it still wont start ?
JA: How old is the battery? Have you checked the battery gauge on the dash?
Customer: its a couple years old , I have also left the charger on it while trying to start it , shows 14.78 volts
JA: What year is your Prius?
Customer: 07
JA: When was your last tune up?
Customer: @68k car has 106k now
JA: Are you hoping to fix this yourself?
Customer: yes
JA: What have you tried so far?
Customer: read back
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Toyota Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: Toyota
Expert:  Toyota Service replied 1 year ago.

Hello. Welcome to Just Answer. Please allow me to assist you. This sounds quite like your 12 volt battery is not accepting a full charge. The tender will not have sufficient amperage to energize the several computers that need to power up to start it; you may have the correct voltage, but not enough reserve amperage. I recommend you replace the 12 volt auxiliary battery to rectify your problem.

Customer: replied 1 year ago.
I have a full size 10 amp charger on it while trying to start it
Expert:  Toyota Service replied 1 year ago.

That may be ok on a discharged battery that is passing the charger voltage thru all of the battery plates. If your aux battery is sulphated between the plates, the charge is not reaching the Gateway ECU or the HV Battery ECU. That would be my estimation of the problem if the 10 amps is not starting the car. Additionally, if you have a smart key, try placing the key fob right next to the start button. Sometimes, the smart key does not send a strong enough signal to the receiver behind the start button. Try placing the fob (if you have a smart key) touching the start button and then see if it starts with your charger attached.

Customer: replied 1 year ago.
HI , I JUST got a new battery today the old one tested ok but I bought it any way , I had disconnected both batterys for several
days and put the new one in today and it made no difference, every thing lights up but the engine won,t start ????????????????????????????
Customer: replied 1 year ago.
Is there a reset button somewhere on the car ?
Customer: replied 1 year ago.
Hello ?
Customer: replied 1 year ago.
why has no one answered my question
Expert:  Toyota Service replied 1 year ago.

Sorry for the delay in getting back to you. No, there is no 'reset' button on this car. What may have happened is the battery tender may have damaged the Gateway ECU. The Gateway ECU is the unit that allows the small battery to energize the rest of the computer in the car via the large battery. You might want to get this taken to a Toyota dealer for diagnosis with a scan tool. Without the results of a good scan, we are now at an impasse.

Customer: replied 1 year ago.
you people promised me you were experts and could solve my problem , are you slackers or just unable to deal with following with what you promised me
Expert:  Toyota Service replied 1 year ago.

Sir. I am a card carrying Toyota Master Certified Technician. Instead of guessing, and speculating you need to replace a four thousand dollar High voltage battery, I suggested you get the car scanned to determine the root cause of the issue. Without the scan, there is no mechanic on the planet earth that can properly assist you and give you the perfect solution to your problem. This is a highly technical vehicle and is easily diagnosed via the Toyota scan tool (which I have but cannot attach to your car). Since I cannot scan the car, I am hesitant to make indiscriminate guesses that costs you money needlessly and may NOT fix the issue. GEt the car scanned, post the results of the scan (the "codes'), and I can direct you instantly. Until then, we both are gambling in the dark.