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GM Historic (OBD I) Diagnostics
5
Field Service
✓Field Service is a special diagnostic mode to monitor fuel system
operation and read DTCs. Some GM service manuals may refer
to this mode as the Field Service Mode Check. This mode works
on vehicles equipped with a 12-pin ALDL connector with a wire
present in pin-B, Diagnostic or Test Enable. The Scan Tool enters
this 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 Field
Service mode.
✓Some 1994 and 1995 vehicles equipped with a 12-pin ALDL
connector with pins A and B shorted will not cause the CHECK
ENGINE light to flash codes.
From the Special Tests Menu:
1. Select Field Service.
•Use
UP
or
DOWN
arrow
key until Field Service is
highlighted.
•Press ENTER.
2. Check vehicle malfunction
indicator lamp (MIL).
•Turn ignition key on, but do
not start engine. The CHECK
ENGINE light should flash.
•Select YES to continue.
•If the light does not illuminate,
either the vehicle does not
support this test mode, the
lamp is burned-out or circuit
problems exist.
✓It is difficult to know exactly which GM vehicles use the Field
Service mode. It is possible to have the Field Service mode
function on the Special Tests Menu, and it not be applicable.
Field Service
Review Data
Print Data
Tool Setup
Special Tests Menu
Does your CHECK
ENGINE light flash?
<Yes> No
Test Availability