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

Chart A-2 No DLC Data Or No MIL Control, Or MIL "ON" Steady:

Malfunction Indicator Lamp Wiring Circuit:

Circuit Description:

There should always be a steady MIL when the ignition is "ON" and engine not running. Battery ignition voltage is supplied to the light bulb. The Powertrain Control Module (PCM) will turn the MIL "ON" by grounding CKT 419 at the PCM.

A steady MIL with engine running suggests a short to ground in the light control CKT 419, or a DTC is set.

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 a Tech 1 scan tool not to read serial data, be sure the scan tool is working properly on another vehicle. If the scan tool is functioning properly and CKT 461 is OK, the 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" with the engine running only.
3. MIL "OFF" with CKT 419 disconnected from PCM indicates that ground circuit was completed through the PCM, not through external short to ground.
4. At this point, the MIL wiring is OK. The problem is a faulty PCM or EPROM. Replace the EPROM only after trying a PCM, as a defective EPROM is an unlikely cause of the problem.