Ignition Diagnostic Monitor (IDM)

PURPOSE

The Ignition Diagnostic Monitor (IDM), an output from the ignition module, provides diagnostic information about the ignition system and drives the vehicles tachometer.

OPERATION
The Powertrain Control Module (PCM) receives the IDM signal and compares it to the Profile Ignition Pickup (PIP) sensor signal.

If for some reason the IDM signal is interrupted, a continuous code is registered in the PCM memory. The stored code indicates, that during recent engine operation the PCM received a PIP signal without receiving corresponding IDM input.

The IDM signal on Dual Plug engines informs the PCM if Dual Plug Inhibit (DPI) is in single or dual plug mode. When the engine is operating in the dual plug mode, the IDM signal matches Spark Output (SPOUT) signal. However, when the DPI signal is 12 volts, the engine operates in the single plug mode and the IDM signal is inverted. That is, when SPOUT is high, IDM is low, and when SPOUT is low, IDM is high.