Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Model number of unit? CPU? Sounds expensive! Warranty?
The run circuit is not complete, when you let off the brake, the mower thinks there is no one in the seat. The seat switch, brake switch and the pto switch all work together to complete the run circuit. Start by checking the seat switch and the it's harness. Next would be the brake switch, Then the continuity between the two switches.
Then the bake switch needs to be checked, it is four wire switch, with two circuits, one is N/O and other side is N/C, check each side with multi-meter , and if it changes from closed to open or open to closed, it is ok.