Reading Service Codes
Engine control system communicates malfunctions to technician through service codes. These service codes are 2-digit numbers representing a particular defect. Service codes are transmitted through STO connector. Service codes are displayed as timed pulses, and may be read with a VOM or Super Star II tester. VOM displays codes by needle sweeps. See Fig 1 . Turn ignition off. Ensure all procedures of EQUIPMENT HOOK-UP have been followed. Engine should be at normal operating temperature.