Medium and Heavy Trucks
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Sounds like the PTO pump is locked up. The reason that you can't start the truck with the PTO is engaged is a safety interlock. Easiest way to check the pump is to disconnect the hydraulic pump from the pto. Put a block off plate on the pto to prevent oil loss. Top off the transmission oil. Start the truck and engage the pto. If the truck does not stall, the hydraulic pump has locked up.