Theory Of Operation
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), 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.