Ignition Diagnostic Monitor (IDM)

Ignition Diagnostic Monitor Schematic:

The IDM circuit is an ECA input from the negative terminal of the ignition coil. The input is a comparison reference, enabling the ECA to determine if the ignition primary circuit has an intermittent fault. When the ECA gets a PIP signal and sends a SPOUT signal to the ignition module the signal should be observed by the IDM terminal at the ECA Fig. 28 (term. 4 DG/Y wire No. 11). Failure to monitor to monitor an ignition coil signal will result in the ECA setting an intermittent failure code into memory. This allows for more diagnostic leverage when attempting to service the vehicle.