Theory Of Operation
WARNING: This page is about a different car, the 2008 Dodge Magnum, 2008 Dodge Charger, and 2008 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 a calibrated limit (see Engine Overspeed Limit chart below), 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.