ray.service Posted January 29, 2016 Report Share Posted January 29, 2016 When we arrived at our last stop a few weeks ago after unhitching and pulling the truck forward I noticed the brake lights on the Volvo were still on. By the time I got everything put up and checked the truck again they were off. HMMMM strange. Pushed the brake pedal a few times and by the time I got to the back of the truck all was OK. Brake lights off. I figured it was just one of those flukes. Next day we’re running out via the highway for supplies and the cruise would not engage. Kept trying an finally it worked. Continued to the store. On the way back same thing. Cruise would not engage after starting out but OK after a few minutes. Time to dig deeper. I had recently changed a few parameters on the ECU so figured that had something to do with it so changed them back the way they were. No help. Pressing the brake pedal would SOMETIMES cause the brake lights to stay on for anywhere from 1 to 10 minutes. I also noticed that the Application gauge would also have a little pressure indicated. Now this explains the cruise control problem. The Volvo (Gen II) uses the micro switch on the brake and clutch pedals to disengage the cruise but uses the stop light circuit to enable it to engage. I also didn’t know if the truck brakes were being lightly applied or not. No trailer connected but assume this would affect the trailer brakes in a bad way. Because it was hard to duplicate I thought maybe the brake light switch was sticking (located on the cab pass thru) and an easy fix. Ordered a new one and replaced. No help. Occasionally I was able to get the brake lights to stay on long enough to do some checking. Pulled black air line from the manifold and the application gauge would go to zero and braks lights would go out. Maybe the brake valve on the firewall itself was sticking so ordered and replaced that. Damn, no help. Frustration setting in. Dug out the pneumatic diagrams and found the black air line for the stop light switch comes from the Trailer Protection Valve. Crawl under the truck and check that out. Pulled off the VENT line and could not blow thru it. IT WAS CLOGGED WITH MUD DAUBER DEBRIS. Replace the vent line with new and all is good. Here’s the rub. I checked the Guide and under Hayes/BrakeSmart/MaxBrake Controllers where it describes placement of the sensor for these controllers. Mine is in the main brake line so this was not affecting my tractor brakes or trailer brakes BUT some of you may have it installed in the black stop light line. If the vent at the Tractor Protection Valve is clogged you could be dragging you trailer brakes. There is no code thrown and the only indication is the stop lights don’t go out immediately or you cruise control won’t engage. I know there were some posts previously about premature brake wear. Might be something to check. In fact might be good to check all these vents on the valves as they are open to the world and bugs. Link to comment Share on other sites More sharing options...
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