pls help ._. 2005 prius with check engine light and p0420, c1378, c1300,c1242 and c1241

First thing to do is to provide basic information and data such as what are the symptoms and problems you are experiencing? Does it drive normally? Brake normally? Go to Ready normally? I would then list the codes and descriptions rather than asking us to look it up, especially if you have already done so. I would then provide steps and tests that you already tried. Like what is the 12v reading, both car Off and in Ready? Have you cleared the codes since you did the work on the 12v battery, front rotors and O2 sensor?

Adding data and background may get you an educated guess versus a wild guess.

Also realize as a brand new member, your responses may take time to show up since a moderator has to approve them first.

 

I agree with the OP, those short descriptions are barely worth bothering with anyway; there's a reason they get called fortune cookies around here.

The place you really want to look up codes when you have them is in the Repair Manual (more info), where there will be a full section on each code to explain what it tells you, what conditions cause it to be set, and steps you can follow to find out why that happened.

Except for the P0420, which may mean the catalytic converter is old and tired (but could also be worth checking the air/fuel ratio and oxygen sensors, or the possibility of exhaust leaks), the other four codes are all brake-system related.

The C1378 is a problem communicating with the brake backup power supply, which is the odd black box in the back of the car next to the 12 volt battery. The C1241 also involves getting or not getting power from that backup box (you can read more about C1241 here; just don't worry about the other codes in that post that you don't have). C1242 is also a (slightly different) power-to-the-brake-ECU code.

Your brake ECU is essentially two computers in one box, "system 1" and "system 2", and they have power supplied to them from different circuits, and they check on each other. The C124{1,2} codes involve them noticing when they should both be getting or not getting power at the same time, but aren't.

The C1300 is a more generic brake ECU mistrusting itself code.

Two things immediately come to mind. You've recently done the 12 volt battery; you should also check its voltage, in case it wasn't fully charged when put in, or may have drained some since. What the 'x' is in 12.x isn't where you need to worry; the Repair Manual will always have you check quickly that it's not below 10 or 11, and give it a good full charge if it is (which means it'll be 12.x when you're done).

The other thing to check is that capacitor box back there next to the battery. That can often get disturbed during 12 volt battery replacement, and its wiring connectors don't always get re-seated completely and securely, and that could turn out to be a lot of the story here.

If you get the battery well charged and you've double checked all the capacitor-box connections, it would be reasonable to clear the codes and see what comes back.

 

... including the bolts that connect it to the floor. Especially if you (or someone else at some point) removed that box (which you don't need to) when you changed the 12V battery.

 

yeah .. 1 of the 1st things that goes is the 12v battery .. people dont discon and the computers eat it down ... sometimes they dont recover if enuf time has gone buy..

the break accumulator .. that thing is a pain .. u can get a used one .. often the pump motor has worn out .. the replacement one i have is from a bit newer car (newer rev number) .. 1st time swap was a real learning curve ... u better have a good back for all the bending over in the engine compartment .. then get yourself a mityvac vaccuum break bleeder ... mine leaks about a pint every 3 weeks ... to me that is liveable because its only about 8 times in 12 months if the car is taking heavy breaking .. if your route is highway even less ...

 

OP hasn't got any codes implicating the pump. They're all about electrical supply to the brake ECU (plus the one that's about the exhaust system).

For the OP, it's never very interesting to say "these warning lights are on but the car still drives OK". That's when you're supposed to get them. If it wasn't, they wouldn't be warnings.

Prii do make a number of interesting sounds. It never hurts to get used to them and learn what each one is, and be able to notice significant changes. For most people, that takes a while of owning the car, and being sort of intentional about learning what the different sounds are, in advance of any immediate concerns.

 

u learn real fast that the little motor noise humming when u open the door .. is the break accumulator pump , after u get the break code pressure low warning light and or the continuous tone and soft spongy pedal ...

 

So you can check that off the list, and proceed with diagnosing the issues being reported.

 

I wouldn't put very much effort into second-guessing the repair manual. The steps you find there for working up the trouble codes that you have are probably as good a guide as you're going to find on the way to pinning down your issue.

They'll be mostly electrical tests of power-supply circuits, judging by the codes discussed in post #3.

 

I'd focus on the C1378.

DTC | C1378 (Blink Code 44) | Capacitor Communication Malfunction

DESCRIPTION
The brake control power supply assembly (capacitor) provides auxiliary power for brake control when an auxiliary battery (12 V) voltage drops.

The FAIL and ENA lines are placed between the skid control ECU and the brake control power supply assembly. Signals indicating that the brake control power supply is in auxiliary mode are sent to the skid control ECU through the FAIL line.

Charge permit prohibition signals are sent to the brake control power supply through the ENA line.

DTC Detection Condition
When either condition below is met:

• Open or short in FAIL line
• Malfunction inside the power back up unit

Trouble Areas

• Harness and connector
• Skid control ECU

If you are the DIY type, I'd further suggest you get a hold of the repair manual pages (see post #3 for more info) for this particular DTC and work through the full troubleshooting work up in the manual.

It is all about checking plugs and harnesses looking for a break in a wire or poor connection in a plug. If all checks out those areas then the brake control power supply assembly is suspect. If that checks out then the skid ECU is suspect.

You might find this post useful.

Good luck.

 

That is not normal. After holding the brake pedal and pushing the start button, the voltage should fluctuate for a few seconds, as you described, but then it should go up to over 13 Volts. When you fully start the car with the brake pedal depressed (ready mode), after a couple clicking sounds from the high voltage battery relays in the rear of the car, the DC/DC converter should raise the voltage in order to recharge the 12V battery.

Maybe you didn't press the brake pedal hard enough while pushing the start button, and the system did not actually go into ready mode. I suggest you try again, and make sure that it actually starts up in "ready" mode. The "ready" light should light up on the dashboard, and the gasoline engine should start after about ten seconds.

 

Yes, that's what's supposed to happen. I think I was so used to that being what happens I didn't even notice that you hadn't said it!