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C1378 & a brake light on an '05

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Ragnorok, Jul 23, 2019.

  1. Ragnorok

    Ragnorok New Member

    Jul 18, 2019
    New Hamshire
    2005 Prius
    Hello All,

    I have an '05 I got last November as an experiment in mileage, which has taken only a few things to keep on the road. The latest thing is the brake light came one, the little red one on the left side. No other indicators, warnings, or anything amiss. The car appears to operate completely normally in all respects, normally being defined by my experience for the last 14k miles.

    I did have the HV battery changed couple of weeks ago, and that tech said there's a C1378 code. At that time the brake light wasn't on, and he seemed to think it wasn't a huge problem but I should look at it. About a week later the brake light came on. Today is about a week after that. Yesterday I took it to have codes read to verify the new battery is up to snuff, and while that does appear to be fine, the C1378 is still there.

    I found a diagnostic procedure somewhere. May have even been here, I don't recall. I've read a number of posts regarding this code all over the 'net, but nearly all of them have "more" than I do, like red triangles or Ready fails. Anyway I started this diagnostic procedure.

    The first step was simple. Got 13.94 V at the Brake Control PS on the indicated pin. The second step is to measure the resistance of the wire in the harness, and that requires removing the "S8" connector from the Skid Control Unit. Found that under the dash, but darned if I can get any of the connectors off. It's not the clips, those are super simple to mash enough to pull the plug out. There's no space and that gargantuan thick harness keeps all four of them pretty much in lock step. I can get them to pull out about a mm, -just- enough that when I push them back they go *click*, so I'm convinced they're re-seated. Can't get any one or even all of them any farther.

    I'm hoping there's some simple trick to this, rather than dismantling half the dashboard to pull out a connector.

    I did find when I started troubleshooting that the guy who replaced the battery unplugged the BCPS. It was plugged back in, and I unplugged and plugged it once or twice to scrap off any crud that may be there. I didn't see any, but hey it was simple. (grin)

    If I had a second BCPS I'd just swap it out, making sure to ground it after reading balmeral's woes. But I don't. I have lots of automotive and electronics experience, a real good DMM, an o'scope, and an OBD that doesn't understand "Prius". lol Any help would be appreciated.

    Thanks for your time...
    - Rags