Chart A-2, Won't Flash Code 12/Check Engine Light On Steady

CHECK ENGINE light will flash trouble codes when either diagnostic request terminal in duty check coupler or DIAG SW connector in fuse block is grounded.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Checks for a grounded light circuit.
Checks if problem is an open circuit in the diagnostic terminal or a faulty ECM.

Fig 1: Chart A-2 Schematic, Won't Flash Code 12 CHECK ENGINE Light On Steady

Fig 2: Chart A-2 Flow Chart, Won't Flash Code 12 CHECK ENGINE Light On Steady