Fail-Safe

TROUBLE DIAGNOSIS


Fail-Safe

The TCM has an electronic Fail-safe mode. This allows the vehicle to be driven even if a major electrical input/output device circuit is damaged.
Under Fail-Safe, the vehicle always runs in third gear, even with a shift lever position of "1", "2" or "D". The customer may complain of sluggish or poor acceleration.
Always follow the " How To Perform Trouble Diagnosis For Quick And Accurate Repair ".
The SELF-DIAGNOSIS results will be as follows:
- The first SELF-DIAGNOSIS will indicate damage to the vehicle speed sensor or the revolution sensor.
- During the next SELF-DIAGNOSIS, performed after checking the sensor, no damages will be indicated.

FAIL-SAFE FUNCTION
The following fail-safe functions allow vehicles to be driven even when sensor, switch or solenoid malfunction occurs.

Vehicle Speed Sensor�A/T (Revolution Sensor)
Vehicle speed sensor�MTR signal is input from combination meter.

Accelerator Pedal Position Signal and Throttle Position Signal
TCM controls the throttle opening angle to a predetermined fixed position to enable driving if a malfunctioning signal is input to TCM.

PNP Switch
When the multiple PNP switch signals are input to TCM, the priority of selector lever position becomes "D", "N", "R", "2" and "1" in order by internal TCM determination.
The use of 4th gear is inhibited until normal operation resumes. Because the hydraulic circuit of the control valve is switched by manual valve according to the selector lever position, however, actual operating condition of vehicle becomes as follows.






Shift Solenoid Valve A and B
If non-standard solenoid signal is sent to TCM, use of certain gears is limited. Refer to chart shown below.






Line Pressure Solenoid Valve
If non-standard solenoid signal is sent to TCM, line pressure solenoid valve is turned OFF to achieve maximum oil pressure.

Torque Converter Clutch Solenoid Valve
If non-standard solenoid signal is sent to TCM, torque converter clutch solenoid valve is turned OFF to release lock-up.

Overrun Clutch Solenoid Valve
If non-standard solenoid signal is sent to TCM, overrun clutch solenoid valve is turned OFF to engage overrun clutch. This will result in more effective engine brake during deceleration.