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Discussion Starter #1
for no particular reason temprementally the above lights started appearing upon starting the car (2004 prius). The brakes do not seem to work either while these on.
if I drive few meters the lights disappear and the brakes start working properly. After this everything works fine until the next power cycle.
also while driving red (!) light comes from time to time for couple of seconds.
It might have started after Aircon recharge.
Any ideas what it might be?
 

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You do realize that your owners manual states to call the dealer anytime you see a red brake warning light.
You get one of two red brake light warnings before complete brake failure on a Prius. One light if the electric hydraulic pump fails and a separate one if the accumulator in the system fails. The pump is not meant to run "all the time" to supply brake pressure. Only to keep the accumulator "charged." If the accumulator fails, you will get a red brake warning light and the pump will now run continuosly until it burns out.
This is a "hot" dealer only problem.
 

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Sounds like the 12v battery is on its last legs. A bad battery will give you strange warning lights. However, yours must have enough power left to allow you to get to the ready mode. Once in READY, the HV battery is supplying most of the 12v requirements as well as attempting to recharge the 12v battery. That's why the warning lights are going out after a short time in READY.
 

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Discussion Starter #4
firepa63 said:
Sounds like the 12v battery is on its last legs. A bad battery will give you strange warning lights. However, yours must have enough power left to allow you to get to the ready mode. Once in READY, the HV battery is supplying most of the 12v requirements as well as attempting to recharge the 12v battery. That's why the warning lights are going out after a short time in READY.
this is what i was thinking miself. The lights usually go of shortly after the engine kicks in and the brakes start working normally. Is there a way of testing the 12v battery? Is the battery available from anywhere else or just toyota?
 

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Please go to Toyota as owners manual prescribes. They are not monsters and if it's a bad accumulator it is not that serious and what you now have is a constantly running pump.
Normally, because of a "charged" accumulator you always have hydraulic pressure to the brake system and "no" red warning lights.
If as you describe when you "power up" you have a red light and no brakes, it signifies that there is no residual pressure account of a leaking accumulator and that the pump has to run several seconds to bring up brake pressure and turn off "Brake Warning light."
This is no problem now because you still have the "pump" working and everything is normal. However, now you have lost 1/2 of your failsafe brake system!
There are only a couple of manufacturers who use the "Bosch" type electrical hydraulic brake system in some of their models and they all have this same potential problem. Mercedes, Cadillac, and the Prius. Toyota is the only one with the "two" brake warning system. When you get the "red light" on the Mercedes or Cadillac you have total system loss of pressure and about six brake applications prior to complete brake failure.
 

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Discussion Starter #6
hyperion said:
Please go to Toyota as owners manual prescribes. They are not monsters and if it's a bad accumulator it is not that serious and what you now have is a constantly running pump.
Thanks for answer. It is very helpful to know your options, and the reason I am asking questions is because I want to know how it works and want to have some information so I understand what the garage is talking about.
I already have the appointment and taking my car to the dealer tomorrow.

what is a rough cost of 12v battery in the uk? :roll:
 

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I don't know the price of the 12v battery in the UK, but in the US it runs around $135. Not sure if that's the installed dealer price, or just the cost of the battery.
 

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firepa63 said:
I don't know the price of the 12v battery in the UK, but in the US it runs around $135. Not sure if that's the installed dealer price, or just the cost of the battery.
thanks, at least i have an idea...
 
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