Intermittent Brake, VSC, ABS (!) lights

Many of the diagnostic codes on the Prius require a special code reader. It is unlikely that any independent repair shop will be able to pull all of the codes unless they specialize in Prius repair.

Most likely you have a problem with the braking system that is being cleared when you remove 12V power, as when you replaced the battery. When the problem is noticed again by the ECU, your Prius logs the error and goes into a backup braking mode.

Find someone that works on Prius. Go to the dealer if that is your only option.

Tom

 

Lights on at startup are usually battery related. Now, the battery may be good, but if you have a poor connection, particularly where the battery ground attaches to the body, the added resistance could be enough to cause a large voltage drop at startup. Next on the list would be a wheel speed sensor. After that, it becomes onerous, a problem with the brake actuator or the circuits that feed it, a problem with the backup power supply, etc.

A Snap-on scan tool with Toyota add-on will be able to read the codes. The freeze frame data could be particularly informative. Otherwise, jumper pins 4 and 13 on the DLC to get flash codes.

 

This all suggests an electrical fault somewhere, where the abs computer does not get high enough voltage. Perhaps high resistance at IG1 relay. Freeze frame data would help.

 

Ok i had these lights come up two days ago and took it to my local toyota dealership. (i dont know much about the prius and the person telling me these things was a service rep not a tech.) They told me I had a faulty 12v and it needed to be replaced. They showed me some fault codes, that i couldnt pull up using torque app. It was a huge list, but only a few codes were being shown being faulty. It was something with abs, vsc, and something to do with a/c. They told me that these codes could be thrown bc of a faulty 12v. They told me that they would need to replace 12v, reset codes, and work back from there. They quoted me 358 with labor with a 250 battery included in that price to replace 12v and reset codes. Which obviously isnt covered by warranty. Im kind of in the same boat you are in but my brakes dont feel any different with the lights on or off. My lights have came on 3 or 4 times. Couple while starting the car and atleast 1 time while driving (wasnt using brakes at time its was random). So as of right now im going to buy the new prius optima yellowtop and install myself. and hope it was just a faulty 12v. If the lights come back on i will just have to take it back to dealership and have them work back from the 12v like they said and clear the codes (would be nice if covered by warranty) Well i hope i helped a little bit and keep us updated on what you do. Sorry if someone already diagnosed your problem, i just wanted to add my story.

 

seems high, a battery should be less than $140, say $145 with tax, one hour labor should be $85, that's all you need, my first battery change in prius took less than an hour, i could probably do it now in around 30-40 minutes so your stealership is trying to rip you off.

 

If you can't wait to order the Yellow Top online,
buy the Toyota replacement from the stealer and
install it yourself, save ~$80: :rockon:

http://priuschat.com/forums/gen-ii-...2v-battery-replacement-preemptive-strike.html

 

if i recall and read correctly.. you're describing a master cylinder failure. as i said.. if memory serves me correct, there are technically 3 types of hydraulic brakes on this: master cylinder, backup, and electronic capacitors.. if your brakes do fail and the capacitors have to drain to give you backup power (that box next to your 12v) an alarm under the dash will sound. that's the time to get really worried. I've heard my alarm a few times. the first time, my brother was in the car while i was getting gas. it scared the $h!- out of him. (not literally) ... the second time i was in the car alone. it scared me too. makes you jump. the 3rd time i was alone again. it's just so loud, i felt violated, i just wanted to cry a little. hehe

this may be off topic since you need more details.... but...

hows your mileage recently? when i had problems like this, it was caused by a faulty ignition coil. my assumptions is that the engine slowly starting to not fire correctly makes an odd jump on the electrical side since it likes to balance things out. for some reason (before the cylinder stopped firing all together) those lights would fire up during long left hand turns. it took me a good amount of time testing to figure out how to reproduce it (good thing i had mountain roads where i lived at the time)... btw.. my problem didn't throw any real codes that pointed to the actual problem. this car doesn't have lights for anything... just lights that let you know something around "this" area (engine compartment... ok.. not that vague...) has acted in a manner that has interrupted something so i'm waving a flag.