Theory Of Operation
WARNING: This page is about a different car, the 2006 Dodge Magnum, 2006 Dodge Charger, and 2006 Chrysler 300. However, it is still accessible from the selected car via links, so may be relevant.
The Transmission Control Module (TCM) monitors the engine speed over the CAN bus. If the engine speed is greater than 4100 + 800 RPM, the TCM assumes that either the information from the Powertrain Control Module (PCM) is incorrect or that a major mechanical problem exist. Once the DTC is set, the TCM will position the transmission gear into neutral to protect the engine and transmission from damage. The transmission will remain in neutral and will not be revaluated by the TCM until the ignition is cycled.