Serial A36441. Started loader, released park brake, went to back up and park brake came on and won't go off. Park brake fuse is good. Went into diagnostic screen. Park brake switch is functional, changes from off to on when switch moved. Park brake relay doesn't change when switch is moved, nor does park brake pressure switch. At the suggestion of a Komatsu tech, I unplugged connector T18, which is the connector for the park brake pressure switch, and bypassed it. Park Brake pressure sensor then showed on, but warning indicator started beeping until we shut loader off. Only other thing that is indicative of a problem is when you let the auto-shutdown timer operate to kill the loader, if the park brake switch is "off", it will beep trans fault. If it shuts down with the park brake switch on, it is fine, other than the park brake won't come off when you start it.
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is it possible that the park brake pressure is not being maintained once the PB switch is operated in the cab causing the system to shut down and put the HST transmission into neutral. Any codes coming up with this fault?. When you find the issue could you please post what the cause was. I'm interested to know what this fault would be. kind regards
Since the monitor was showing the switch was functional, but not the relay or the pressure switch, but I could verify the switch was functional, I chose to replace the relay and the pressure solenoid valve. I could have swapped the relay first, and then the solenoid if the relay didn't fix it, but I need this loader, and I had to drive 180 miles to get the parts, and I didn't want to leave anything to chance. I am a little inexperienced in checking relays and solenoids, so the parts cannon got fired, lol. Problem solved for now. I am a bit irritated, however, that my service advisor is recommending to not use the auto-shutdown timer, as he believes that it could be related. He claims it only kills the power to the engine ECU, but keeps everything else energized, it interrupts the signals for the hydraulics and park brake differently than switching the key off. I was really looking forward to having the auto-shutdown since the machine will be mainly loading gravel, and I liked the idea of not having to sit there and wait to shut the engine off before I could get back in the truck.