• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 5 – 11GM Historic (OBD I) Diagnostics5Field Service✓ Field Service is a special diagnostic mode to monitor fuel systemoperation and read DTCs. Some GM service manuals may referto this mode as the Field Service Mode Check. This mode workson vehicles equipped with a 12-pin ALDL connector with a wirepresent in pin-B, Diagnostic or Test Enable. The Scan Tool entersthis mode by grounding pin-B: shorting pin-B to pin -A (ground).✓ Field Service mode can be operated with KOEO or KOER.✓ Vehicles equipped with climate control computers do not use FieldService mode.✓ Some 1994 and 1995 vehicles equipped with a 12-pin ALDLconnector with pins A and B shorted will not cause the CHECKENGINE light to flash codes.From the Special Tests Menu:1. Select Field Service.•Use UP or DOWN arrowkey until Field Service ishighlighted.•Press ENTER.2. Check vehicle malfunctionindicator lamp (MIL).•Turn ignition key on, but donot start engine. The CHECKENGINE light should flash.•Select YES to continue.•If the light does not illuminate,either the vehicle does notsupport this test mode, thelamp is burned-out or circuitproblems exist.✓ It is difficult to know exactly which GM vehicles use the FieldService mode. It is possible to have the Field Service modefunction on the Special Tests Menu, and it not be applicable.Field ServiceReview DataPrint DataTool SetupSpecial Tests MenuDoes your CHECKENGINE light flash? NoTest Availability
