User Manual

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• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • GM Historic Diagnostics
4
Field Service Mode can be operated with the ignition Key On-Engine Off (KOEO)
or with the Key On-Engine Running (KOER).
✓ Vehicles equipped with climate control computers do not use Field Service.
✓ Some 1994 & 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.
Select Field Service from the GM
Function List and press
(17(5 .
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 Function List, and it
not be applicable.
If Check Engine light operates, the Field
Service screen displays. Pressing
(17(5 toggles the short to Pins A & B On
and Off as indicated on the tool’s screen.
Continue with either the KOEO procedure or KOER procedure. When done, press
%$&. to return to the GM Function List.
✓ While in Field Service mode, no new trouble codes are stored in the vehicle’s
memory.
KOEO Procedure
With the KOEO (key On engine Off), Field Service can check relays, solenoids
and the idle speed motor, and obtain DTCs using the CHECK ENGINE light.
1) Turn ignition Key ON but DO NOT Start Engine.
2) On scan tool, place Field Service On.
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