2010 Prius ABS C1391 code

It's $15 to get into techinfo.toyota.com for two days ... if I were already in to look something else up, I'd certainly look up your C1391 for you. The abridged lists floating around already call it an "accumulator leak malfunction", for all the help that gives you, but in the manual there will be a page number next to the code, and flipping to that page will take you to much more useful information about what exactly happens to set the code (which may help you make sense of what you're seeing) and what things to test in what order to pin down the cause.

Ultimately, a leak that prevents the accumulator from holding proper pressure is either an external leak or an internal one.

An external one (fluid leaving the system) will have the level going down over time, and somewhere on the car, there will be escaping fluid.

An internal one could be an ill-sealing valve or master-cylinder plunger that allows the pressurized fluid to sneak past and return to the reservoir. None actually leaves the system, it just won't stay in the accumulator, and the pump has to run more to make it up.

An internal leak like that could be either in the accumulator/pump assembly, or in the master-cylinder/booster/actuator/ECU/partridge/peartree assembly, and they're both pretty spendy but the pear tree takes top honors in that category, so a good plan would be to do enough testing to figure out which one's at fault.

In the Techstream software, you have not only code reading and data monitoring, but also active tests that allow flipping individual valves in the actuator open and closed to see what happens (while reading the data back from the several pressure sensors that are already built in), so that could come in handy in diagnosis. Diagrams of the system are in the New Car Features manual (always easier to make sense of something when you know what you're looking at).

Plenty of reports on PriusChat of people putting in either part from the used market, for obvious reasons. If you go used for an accumulator assembly, try not to get one of the units subject to the recall.

-Chap

 

has anyone simply removed the fuse (S) from the ABS, SYSTEM? RESULTS. I HAVE A 2011, I Spoke with Toyota Corp customer service, as my 2008 with same failure was covered. I own both gen2 and Gen3. I hope to hold off till Toyota gives in and covers the Gen3 cars. I'm considering an attempt to make this issue public? Any thoughts? I am a retired, Mazda Toyota Tech,

 

Pull the fuses and you have the failsafe braking, which (a) has no power assist, and (b) acts only on the front brakes, the effects of which on emergency maneuvering I can't easily predict. It certainly isn't a 'solution' I'd use long-term.

-Chap

 

Thanks, I tried and was not good as you said. I now see (after adding fluid to the master) it had turned off the dtc, lamps. Now it is back and master is more full than I left it. I reset the code again as it is not safe while it sees the defect. rr locks up on hard braking. Toyota says no coverage for 2011 on C1391. I need an independent Toyota Tech as Olafe Toyota sell the accumulator for $702.

 

You do want an independent tech (or a Techstream-equipped laptop of your very own and tools, if DIY is a possibility), but it's premature to be looking at price of the accumulator. In your 2010, the "accumulator assembly with booster pump" is one assembly, and the "brake master cylinder with booster and actuator" is another assembly, but the problem you're having could still be in either one, consistently with the information we have so far. The first assembly is the one you have the price of, but the other one is where most of the valves in the system are, and it's definitely possible for one of those to be the culprit.

700 for the accumulator is not small change, and the mcyl/actuator is likely to be even more than that, so it's in your interest to gather more evidence of which one is at fault before going shopping. You could probably gather some of that evidence using the data list and active tests in Techstream, as I mentioned earlier. A technician working at a shop on the clock might just skip the think part and replace one assembly, and if that doesn't fix it, replace the other one, but that's easy for him, because he's playing the game with your money.

-Chap

 

First it's a 2011, second I'm a retired Toyota Mazda,Tech. And shop owner from NY, retired in FL. I have filled the master, the code went away and returned. The pump is Nearly continuous. I have Techstream. And have cleared the code after saving it. When cleared the brakes are normal. When code is present brakes require more effort and RR, WILL LOCK PREMATURELY?

 

Based on your response I will consider a local hybrid specialist. But his quote is 2500. Better than the dealer, but we need to be sure all instances are reported to hope Toyota includes 2011 in the extended coverage along with all the 2010s. Thanks

 

Sorry, I scrolled up too far and looked at the original post, where the car was a 2010.

This sounds like something you've probably got the skills to do, if you've got Techstream and access to TIS. The challenge will be finding a way to isolate the problem to which of the two assemblies could be involved ... unless you just wanted to try replacing one, then the other.

-Chap

 

Get both used from car-part $75 each. Get large jug of dot 3 supertech brand cheap. Put stainless safety wire on brake pin for pedal. Put masking tape on lines and write w perm marker. Maybe do new sp plugs since ur there. Job is 6h. If u pay urself $100/hr you still save thousands.

 

Had the same code..I added brake fluid and all the lights went out ...use DOT 3 .... my problem solved

 

Will you please remember to post back here if this changes?