Ignition Diagnostic Monitor (IDM)

Ignition Diagnostic Monitor Schematic:

The Ignition Diagnostic Monitor (IDM) circuit is an Powertrain Control Module (PCM) input from the negative terminal of the ignition coil. The input is a comparison reference, enabling the PCM to determine if the ignition primary circuit has an intermittent fault. When the PCM gets a Profile Ignition Pickup (PIP) signal and sends a Spark Output (SPOUT) signal to the ignition module, the signal should be observed by the IDM terminal at the PCM. Failure to monitor an ignition coil signal will result in the PCM setting an intermittent failure code into memory. This allows for more diagnostic leverage when attempting to service the vehicle.