Prius Gen 2 code C1311 C1377 - solved

Anyone have any other suggestions?

Replaced front pads, rear shoes, hardware & rear wheel cylinders. Completed scanner assisted brake bleed while also replacing 170k mile brake fluid. Cleared code history but still had C1311 & C1377 persist, along with the red brake warning light. No ABS, VSC, etc. amber lights or red triangle. Braking is straight and true, but high effort, and in extremely hard braking I can get the front brakes to skid on gravel, otherwise fine. ABS pump actuates.

Went through and replaced all four ABS related relays under hood, along with new micro fuses after giving each slot a drop of De-oxit. The 12 volt battery is a fully charged, 3 month old, OEM Toyota replacement with a new positive clamp, negative cable, and new grounding bolt. Also swapped out hybrid regenerative brake control module with a known to be good example, but still no joy - the red brake light yet mocks me.

The under-hood fuse box is undamaged and seals as well as can be expected from the design. None of the fuses or relays that I removed and replaced had any signs of corrosion beyond what I'd call normal oxidation, but I treated each slot w/ a drop of De-oxit anyway.

The initial brake fail was attributed to failed rear brake hardware that allowed one rear wheel cylinder to hyper-extend, hence the above mentioned repairs, and the front pads were an "as long as I'm here bleeding brake fluid" kinda thing, but those rotors were fine, calipers well greased, etc. Wheel sensors properly attached and functioning.
My assumption was that since the brake control module is basically a bunch of capacitors, that possibly one or several of them might have failed, but a different unit changed nothing. Also, swapping out the relays and fuses seemed to make a lot of sense since the other code flagged Main Relay #1, but that didn't do it either.

Not sure where else to go from here. I've about run out of ideas of things to try. Hadn't messed with anything wire harness related, but I guess I can start testing for continuity there? I do not know...

 

You need to get a copy of the factory service manual to study the wiring diagrams and do some voltage testing. C1311 pretty much says that the voltage at ecu pin BS1 (from ABS No.1 relay) doesn't match the commanded state. (ie, the relay is supposed to be ON but the voltage at BS1 is too low, or vice versa).

Also having a fully capable scantool with bidirectional controls would be handy, so you could command the relay on or off and do voltage tests at the ecu connector.

Posted via the PriusChat mobile app.

 

Suggestion on where to get a copy of that service manual? I thought I'd seen pdf somewhere (maybe here on PC) but don't recall where. Thanks very, very much for the direction, and I do happen to have a bi-directional scanner, but I've not done much with it beyond DTS scans and brake bleeding.

What has me scratching my head is that I hadn't previously messed with anything electrical in the brake system, so bent pins and bad connectors seemed a stretch, but I suppose swapping hybrid packs in and out could have chuffed, pulled or skinned something.
Thank you again very much for the direction, as this one's been a seriously nagging pita.

SM-N960U ?

 

Having a hard brake means something serious is wrong. You may be in failsafe mode.

Very few aftermarket scanners do a Prius brake setup and bleed correctly. Techstream is the way to go there.

There is a gigantic patched together gen2 repair manual floating around but its hard to search much less load. All the links are broken making things worse.

Better to go with a weekend subscription to TIS and read, link and download specific sections for your issues.

https://techinfo.toyota.com/techInfoPortal/appmanager/t3/ti?_pageLabel=ti_whats_tis&_nfpb=true

Or simply let a dealer diagnose and perhaps perform the Techstream brake setup and bleed.