Theory of Operation
WARNING: This page is about a different car, the 2011 RAM Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
This diagnostic is testing for an internal Powertrain Control Module (PCM) failure. The PCM redundantly calculates engine speed based crankcase speed sensor. This calculation is done in a different part of the PCM than the primary calculation. It detects if the primary engine speed calculation is lower than the redundant calculation by more than a calibrated amount 675 RPM for a calibrated amount of time two sec. The PCM will light the ETC lamp when the diagnostic runs and fails. The light will remain on for the drive cycle or until both calculations agree for two seconds.