GM Historic (OBD I) Diagnostics
KOEO Procedure
In the KOEO Procedure, 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.
3)The Check Engine light will begin to flash codes. Each DTC is displayed three (3) times. The DTCs are displayed starting with the lowest numbered one. After all DTCs are displayed, the sequence keeps repeating until the ignition key or Field Service mode is turned OFF.
—Count CHECK ENGINE Light Flashes to obtain trouble codes. The first digit is sent first. A short pause separates digits while a long pause separates each DTC. All codes contain 2 digits.
—DTC 12 (No RPM reference pulse) should display first since the engine is not running. If not, problems exist in the PCM or Check Engine light circuitry.
Code 12 will look like:
FLASH-pause-FLASH-FLASH — long pause.
Code 23 will look like:
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4) When Field Service Mode is ON, most computer controlled Relays and | 5 |
Solenoids will be turned ON, except for the fuel pump relay and fuel |
injectors. Toggle the Field Service Mode On and Off.
❒Use a voltmeter to measure Relays and Solenoids input voltage to verify On/Off conditions. An ohmmeter could be used to check the continuity between the relay’s switch terminals.
❒The Idle Air Control (IAC) valve is fully seated to the zero position by the PCM.
❒The Exhaust Gas Recirculation (EGR) solenoid is energized for 25 seconds.
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