Immediate Shut Down (ISDN) 1 and 2

The TCM receives the redundant ISDN1 and ISDN2 signals from the high voltage traction battery. Under normal operating conditions the TCM monitors both ISDN circuits for low voltage battery voltage. If at any time during normal operation the TCM detects voltage drop on both ISDN circuits, the electronically controlled continuously variable transaxle (CVT) immediately stops delivering any torque, reduces operating voltage to under 50 volts, and discharges the high voltage capacitors. This action disables the vehicle until the key is cycled OFF and ON. The voltage drop on both ISDN circuits is usually a result of some other concern in the hybrid electric system, and DTCs indicating root cause may be stored in other modules. If the voltage drop is detected on only one of the ISDN circuits, the TCM continues its operation and stores the appropriate DTC. The voltage drop on only 1 of the ISDN circuits usually indicates an open ISDN circuit.