The GM computer is tucked out of sight and out of danger under the dash, and the diagnostic plug is mounted under the steering column. From there, the wiring harness is run to the sensors in the engine compartment and down below. All the GM EFI sensor functions are retained. Hi-Tech supplies the plug-in key and instructions that allow you to troubleshoot the system. Or the unit can be set and serviced by any technician with GM diagnostic equipment.