Chart A-2 Service Engine Soon Light ON Steady

Won't Flash Code 12:

Chart A-2 Wiring Diagram:

CIRCUIT DESCRIPTION:

There should always be a steady "CHECK ENGINE" light when the ignition switch is "ON". With the "Diagnosis Switch" terminal grounded the ECM will flash a Code 12, followed by any additional trouble code(s). A steady "CHECK ENGINE" light suggests a short to ground or an open "Diagnosis Switch" circuit terminal.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. This will check for a grounded light circuit.

2. This will determine if it is an open "Diagnosis Switch" terminal circuit or a faulty ECM.