Chart A-2 No DLC Data or No MIL Control or MIL on Steady

Chart A-2 No DLC Data Or No MIL (Check Engine) Control, Or MIL "On" Steady:

System Check Schematic:

CIRCUIT DESCRIPTION
Battery voltage is supplied through the ignition switch directly to the lamp. The Powertrain Control Module (PCM) controls the lamp and turns it "ON" by providing a ground path through CKT 419 to the PCM. There should always be a steady Malfunction Indicator Lamp (MIL) (Check Engine) when the ignition is "ON" and engine is "OFF."

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. If there is a problem with the PCM that causes the Tech 1 scan tool to not read serial data, be sure that the scan tool is working properly on another vehicle. If the scan tool is functioning properly and CKT 800 is OK, the Erasable Programmable Read Only Memory (EPROM) or PCM may be at fault for the "NO DLC" symptom.
2. The Tech 1 has the ability to command the MIL "ON" and "OFF."
3. MIL "OFF" with CKT 419 disconnected ftom PCM indicates the ground circuit was completed through the PCM, not through an external shofl to ground.
4. At this point, the MIL circuit is OK. The problem is a faulty PCM or EPROM.