The j1850 is a bus for diagnostics and data sharing. If you see the code displayed on dashboard there could be few issues.
- Loose fuse
- Bad ground
- Bad ignition key switch
- Battery voltage low
- Short to ground
You should get a OBD2 reader to find out more. OBD means on board diagnostics for vehicle self diagnostics as in this video:
There is a interface on a obd2 connector.
Engine codes begin with a P and those will help you find the exact problem.