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, NGS, or Super Star II tester. VOM displays codes by needle sweeps. See Fig 1 .
Turn ignition off. Follow all procedures of EQUIPMENT HOOK-UP. Engine should be at normal operating temperature.