Rear Brake lights stuck on all the time

Driving through slush would be, I would think, more of a factor for the more exposed connectors like those at the wheel sensors. The connector at the brake ECU is at least up under the cowl and fairly sheltered from the immediate road conditions ... but I guess you might have a bit of a corrosive atmosphere there in general, and it's still out in that.

 

I am sure if it happened to me that's exactly what I would do, and if I didn't see a correctable problem at the connector itself, I would even investigate whether it's possible to open that side of the assembly and get the circuit board out for a good looking over. I have not seen anyone here report trying that before, or how far they got. It is also what I would do if I ever got the hazard-flashers-go-with-road-speed syndrome. If there turned out to be a way to get to the circuit board without damage, and find a correctable issue, and without having to muck with all the hydraulic disassembly of exchanging the whole unit, I would report that here as a success.

Naturally, as that's an unofficial and uncharted procedure, I'd have to accept the risk that either (a) it doesn't come apart that way at all, or (b) it does, but that wrecks it and then a replacement is needed anyway.

There's a good chance I would really begin by buying the cheapest non-guaranteed probably-broken salvage unit I could find, just to explore how it goes together, in the comfort of a well-lighted workbench.

Or if anybody ever had one replaced because of the hazards-with-road-speed syndrome, see if they could be talked into sending the old one to me.

 

In your case there are still some simple checks with a multimeter I would want to make before even digging in for the ECU, or I would want a rundown of exactly what and how the dealer technician checked, detailed enough to be sure it covered what I would have checked.

 

I am also facing the same situation you are although my brake lights are constantly on after I replaced my actuator (master cylinder) with a used one. I was getting the C1391 code because of which I got both my accumulator and actuator replaced. The code and dashboard lights went away afterwards; however the brake lights remain on.

Were you or the dealer able to figure out what the problem was?

 

Thanks. For me, it turned out to be a faulty brake switch. It appears we damaged it while replacing the actuator or the master cylinder. Replacing it with a new brake switch solved the issue.

 

Good to know that you weren't facing the same situation. The one in this thread involves a C1380 code and isn't the brake pedal switch.

 

My 2010 Prius has similar problems - everything was fine until 5 weeks ago - then came all the warning lights, etc. I ordered a new front wheel speed sensor, but that gave no change. One day later the brake lights started to stay on continuously; and also Techstream wasn't able to fix the Linear Solenoid Valve Offset (one of the original trouble codes, but now just history).
2 days ago, there were a dozen codes in Techstream under ABS/VSC/TRAC, but today only C0200 and C1380 remain, plus P1578.
The car only sat in the driveway, so I'm suspicious that there may be connector problems at an ECU.
I did replace the front sensor but the bearing is noisy, so that will be replaced only if I can fix the lights.

Since the other trouble code points to the Stop Light Control Relay, I ordered a used one from eBay and I now have the "bad" one apart for a look. It is an electronic "relay" circuit with IC's and power devices, and there is a missing bit of copper circuit connected to the ACC input pin. If I can repair the copper trace, should I then try it in the car or check other things first?
Would it be worthwhile to burrow in to the ABS assembly to check all of the ECU connectors for corrosion?

Thanks in advance for any suggestions you may have

 

It may have been only a cold solder joint....
paul

 

What's your approx location? Any evidence of rodents?

 

Any programs that train rodents to solder better?

 

St. John's, NL, Canada - no evidence of rodents, but we're near the ocean so that plus road salt during our winters leads me to suspect corrosion

 

I did teach a workshop course for a few terms that had a soldering component, but this circuit board has surface-mount components - beyond my experience

 

I reinstalled the stop light relay and there is no change - brake lights are still on.