Fail Safe

TCM


Fail-safe

The TCM has an electrical fail-safe mode. In this mode TCM operates even if there is an error in a main electronic control input/output signal circuit.

FAIL-SAFE FUNCTION
If any malfunction occurs in a sensor or solenoid valve, this function controls the CVT to make driving possible.

Secondary Speed Sensor
The shift pattern is changed in accordance with throttle position when an unexpected signal is sent from the secondary speed sensor to the TCM. The manual mode and overdrive control mode are inhibited, and the transaxle is put in "D".

Primary Speed Sensor
The shift pattern is changed in accordance with throttle position and secondary speed (vehicle speed) when an unexpected signal is sent from the primary speed sensor to the TCM. The manual mode and overdrive control mode are inhibited, and the transaxle is put in "D".

Transmission range Switch
If an unexpected signal is sent from the transmission range switch to the TCM, the transaxle is put in "D".

Manual Mode Switch
If an unexpected signal is sent from the manual mode switch to the TCM, the transaxle is put in "D".

CVT Fluid Temperature Sensor
If an unexpected signal is sent from the CVT fluid temperature sensor to the TCM, the gear ratio in use before receiving the unexpected signal is maintained or the gear ratio is controlled to keep engine speed under 5,000 rpm.

Secondary Pressure Sensor
- If an unexpected signal is sent from the secondary pressure sensor to the TCM, the secondary pressure feedback control is stopped and the offset value obtained before the non-standard condition occurs is used to control line pressure.
- If secondary pressure sensor error signal is input to TCM, secondary pressure feedback control stops, but line pressure is controlled normally.

Line Pressure Solenoid Valve
If an unexpected signal is sent from the solenoid valve to the TCM, the line pressure solenoid valve is turned
OFF to achieve the maximum fluid pressure.

Secondary Pressure Solenoid Valve
If an unexpected signal is sent from the solenoid valve to the TCM, the secondary pressure solenoid valve is turned OFF to achieve the maximum fluid pressure.

Torque Converter Clutch Solenoid Valve
If an unexpected signal is sent from the solenoid valve to the TCM, the torque converter clutch solenoid valve is turned OFF to cancel the lock-up.

Step Motor
If an unexpected signal is sent from the step motor to the TCM, the step motor coil phases "A" through "D" are all turned OFF to hold the gear ratio used just before the non-standard condition occurred.

Lock-up Select Solenoid Valve
If an unexpected signal is sent from the solenoid valve to the TCM, the lock-up select solenoid valve is turned
OFF to cancel the lock-up.

TCM Power Supply (Memory Back-up)
Transaxle assembly is protected by limiting the engine torque when the memory back-up power supply (for controlling) from the battery is not supplied to TCM. Normal status is restored when turning the ignition switch
OFF to ON after the normal power supply.