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Originally Posted by sanders71
2001 2500HD 8.1L Allison 5 speed transmission. The ABS indicator and brake light came on during a few easy stops where the abs activated even on dry pavement and slow speeds. During the same trip and just a few miles later, the transmission kicks out of gear and the indicator flashes. Putting in neutral and back into drive the truck will move but only for a few feet before it does it again. Does the same in any gear, neutral "resets" it then it kicks out again. Only code I'm getting is a p1781 which I think is a transmission code but not sure. Could these two issues be related as they both occurred at the same time? I'm kind of at a loss right now trying to diagnose. Thanks
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The ABS activating is probably a bad/dirty ABS/Wheel Sensor. I know on my old '03, my ABS/Wheel Sensor was filthy on the passenger side. I was also exhibiting the same symptoms you were having while coming to a stop. Cleaned it up and it lasted another month before it completely failed. Fairly easy piece to replace.
Not sure about the transmission though. I don't think there is any relation to your ABS issue. Could just very well be a coincidence. Or may be the ABS engaging when it shouldn't is causing the transmission to act screwy. I would try and replace the faulty ABS sensor first and see what happens. One way to determine which sensor is going back is to hit the brake at a low speed, let go of the wheel and when the ABS engages, see which way the truck turns. So if it goes to the right when the ABS engages, then you know the passenger front sensor is bad/dirty. Otherwise, you'll need a Tech2 to scan the OBDII to determine which sensor is going into fault.