- Preliminary Information

1985

These models are not equipped with a Check Engine Light (CEL) on the instrument panel, therefore Diesel Diagnostic Check (DDC) tool No. J-34750, or equivalent should be used when checking the DEC system. As a bulb check, the DDC tool Check Engine Light (CEL) will be illuminated when the connector for battery voltage is connected. When the DDC tool is connected to the ALDL, with ignition switch in On position engine not running, the tool CEL will indicate a code 12. The code is displayed by a flashing light code. Code 12 is indicated by one flash, short pause, two flashes then a longer pause. This will repeat three times and if no other codes are stored in the system, the light will continue to flash code 12. Begin testing with the Diesel Diagnostic Circuit Check.