Safety Functions
The safety functions are designed to safeguard against inappropriate actions by the operator as well as against system malfunctions. The system prevents reverse gear from being engaged at high forward speeds and prevents manual downshifts at excessive engine speeds; these functions are not operational in mechanical limp-home mode.
The TCM constantly monitors the transmission for faults. In the event of a problem the TCM will adopt a "limp home" mode in which only P R N D - (selector in D but only fourth gear is enabled) are available. The operator will be made aware of certain faults by an instrument panel warning.
The electrical and diagnostic system has been designed such that system integrity is protected at all times, the safety concept being based on the following three points:
- The hydraulic system has "fail-safe" characteristics regarding its electrical operation, such that should the power supply be lost to the electro-hydraulic actuators the transmission will initiate a limp-home mode.
- Recognition of critical shift operation by monitoring the last element in the signal path, i.e. the solenoid valve, and checking by means of redundant measured variables, i.e. engine speed, input speed and output speed.
- Each time the vehicle is started there is a check on the entire safety hardware and the associated program parts and signal paths. A malfunction in this part of the system, or triggering of the safety circuit, is communicated to the operator through the illumination of the transmission warning lamp.