Transmission fault monitors must take into account failures from both hardware and software. Hardware failures, which, result due to a complete loss of function or through wear over time, are a predictable and expected failure source. Software faults, however, are unpredictable, since the fault is always present, and simply needs the right set of circumstances to occur.
In automatic transmission systems, where there are no hydraulic or mechanical interfaces to prevent improper engagement of the various friction elements, the need for reliable and predictable software becomes paramount to avoid conditions where the transmission fails to transmit torque to the driving axles. In addition, the monitor must take the necessary measures to avoid false positive detection of an impending transmission tie-up.