My 2012 Prius C has about 110k miles and has been parked in my gauge for over 2 years. Three months ago I relubed the front caliper pins, cleaned rear drum brakes, and tried to change brake fluid. The auxiliary battery gave up before I could finish brake fluid change. Today I installed a Harbor Freight AGM battery and the car started fine. However, a few warning lights stay on (Brake, Brake System Warning, Slip Indicator, and ABS). I took a short drive and didn't feel anything seriously wrong. I searched and saw quite a few threads on PriusChat, but still not sure what apply to mine. BTW, I left my ODB2 out of town and cannot scan error codes. Any idea is welcome.
While you're away from your scan tool out of town, get the codes using light blinks, and post them here.
If you search the forum for something like blink codes jumper tc cg you should probably find a few posts here and there.
Here are the Tc & CG blinks: Brake System Warning light ((!)): 4, 6 Slip Indicator light: 4, 5 ABS Warning light: 4, 2 How do I interpret them?
42 on the ABS light is "go look at your ECB light." 45 on the VSC light is "go look at your ECB light." 46 on the ECB ((!)) light is DTC C1246. It can be used to report five different weird things about the reading from the master cylinder pressure sensor. There are INF codes to tell you which of the five weird things happened: either the voltage supplied to the sensor was out of range for at least a twentieth of a second, or the pressure reading was outside of [0.4V, 4.92V) for at least that long, or you weren't braking and it was outside of (0.2V, 0.88V) for at least 3 seconds, or the reading doesn't make sense compared to the stroke sensor or the wheel cylinder pressure, or the pressure fluctuated weirdly. But light blinks can't give you the INF codes; you would need a scan tool to get those. There are five pages of troubleshooting steps in the repair manual that you can follow to pin down the problem. Toyota Service Information and Where To Find It | PriusChat edit: hmm, from your profile, I looked in a Gen 3 liftback repair manual and posted a Gen 3 liftback diagram. But I think the c is pretty similar in the brake department. (?)
Your explanation makes a lot of sense, considering that the issue occurred during brake fluid change when battery was out of juice. BTW, I have two Prii: a Gen-3 Prius II and a Prius-C trim 2.
Can you send a link to the webpage that explains how to activate the Tc & GG blinks? I have a 2013 Prius and I'm in the same situation. I still can't find a post on how to activate the blink diagnostics.