Automatic Transaxle System Fail-Safe Chart

Drivetrain. Corolla. Zre142 Aze141
U341E Automatic Transmission Transaxle. Corolla. Zre142 Aze141

  1. FAIL-SAFE

Automatic Transaxle System -- Fail-Safe Chart



FAIL-SAFE
This function minimizes the loss of the ECT functions when any malfunction occurs in each sensor or solenoid.

  1. Vehicle speed signal (SPD):
    When there are problems with vehicle speed signals, 4th upshift is prohibited.

  2. Input turbine speed sensor NT (Speed sensor NT):
    When the input turbine speed sensor has a malfunction, 4th upshift is prohibited.

  3. ATF (Automatic Transmission Fluid) temperature sensor:
    When the ATF temperature sensor has a malfunction, 4th upshift is prohibited.

  4. Shift solenoid valve SLU:
    If the ECM detects a malfunction in the solenoid valve SLU, it turns the valve off.

  5. Shift solenoid valve SLT:
    When the solenoid valve SLT has a malfunction, 4th upshift is prohibited.

  6. Engine coolant temperature sensor:
    When the engine coolant temperature sensor has a malfunction, 4th upshift is prohibited.

  7. Knock sensor:
    When the knock sensor has a malfunction, 4th upshift is prohibited.

  8. Throttle position sensor:
    When the throttle position sensor has a malfunction, 4th upshift is prohibited.

  9. Shift solenoid valve S1 and S2:
    Fail safe function:
    If either of the shift solenoid valve circuits develops an open or short, the ECM turns the other shift solenoid "ON" and "OFF" in order to shift into the gear positions shown in the table below.
    The ECM also turns the shift solenoid valve ST OFF at the same time. If both solenoids malfunction, hydraulic control cannot be performed electronically and must be done manually.
    Manual shifting as shown in the following table must be done (In case of a short circuit, the ECM stops sending current to the short circuit solenoid).
    Even if starting the engine in the fail-safe mode, the gear position remains in the same position.

    Normal
    		Solenoid Valve
    		S1
    		ON
    		ON
    		OFF
    		OFF
    S2
    		ON
    		OFF
    		OFF
    		ON
    Gear Position
    		1st
    		2nd
    		3rd
    		4th (O/D)
    S1 Malfunction
    		Solenoid Valve
    		S1
    		X
    S2
    		ON → OFF
    		OFF
    		OFF
    		ON
    Gear Position *1
    		3rd
    		3rd
    		3rd
    		4th (O/D)
    S2 Malfunction
    		Solenoid Valve
    		S1
    		ON
    		ON
    		OFF
    		OFF
    S2
    		X
    Gear Position *1
    		2nd
    		2nd
    		3rd
    		3rd
    S1 and S2 Malfunction
    		Solenoid Valve
    		S1
    		X
    S2
    		X
    Gear Position *1
    		3rd
    		3rd
    		3rd
    		3rd

    1. *1: Actual gear shift (gear position) under fail-safe operation.
    2. X: OFF (the ECM stops sending current to a malfunctioning solenoid valve)
    3. →: Condition in the electrical malfunction is shown on the left of "→".
      Condition in the fail-safe mode is shown on the right of "→".