Chart A-1, Won't Flash Code 12, No Check Engine Light: Notes

There should always be steady CHECK ENGINE light when the ignition is on and engine is off. Battery voltage is supplied directly to the light bulb. The ECM controls the light and turns it on by providing a ground path through the Purple wire.

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

ECM battery feed terminals B1 and C16 are protected by a fusible link in fuse/relay block, near battery.
If ECM terminals B1 and C16 have voltage, then either ECM grounds or ECM is faulty.
Using test light connected to 12 volts, probe each of the system ground circuits to ensure good ground is present.