Nissan Sentra Service Manual: System

CVT CONTROL SYSTEM

CVT CONTROL SYSTEM : System Diagram

CVT CONTROL SYSTEM : System Description

DESCRIPTION

• CVT detects the vehicle driving status from switches, sensors and signals, and controls the vehicle so that the optimum shift position and shift timing may always be achieved. It also controls the vehicle to reduce shift and lockup shock, etc.
• If a malfunction occurs on the electric system, activate the fail-safe mode only to drive the vehicle.

MAIN CONTROL CONTENTS OF TCM

List of control items and input/output

*: If these input/output signals show errors, TCM activates the fail-safe function.

CVT CONTROL SYSTEM : Fail-Safe

TCM has a fail-safe mode. The mode functions so that operation can be continued even if the signal circuit of the main electronically controlled input/output parts is damaged.

If the vehicle shows following behaviors including “poor acceleration”, a malfunction of the applicable system is detected by TCM and the vehicle may be in a fail-safe mode. At this time, check the DTC code and perform inspection and repair according to the malfunction diagnosis procedures.

Fail-safe function

CVT CONTROL SYSTEM : Protection control

The TCM becomes the protection control status temporarily to protect the safety when the safety of TCM and transmission is lost. It automatically returns to the normal status if the safety is secured.

The TCM has the following protection control.

CONTROL FOR WHEEL SPIN

CONTROL WHEN FLUID TEMPERATURE IS HIGH

TORQUE IS REDUCED WHEN DRIVING WITH THE REVERSE GEAR

REVERSE PROHIBIT CONTROL

Line pressure control

LINE PRESSURE CONTROL : System Description

SYSTEM DIAGRAM

DESCRIPTION

Highly accurate line pressure control (secondary pressure control) reduces friction for improvement of fuel economy.

Normal Oil Pressure Control

Appropriate line pressure (secondary pressure) suitable for driving condition are determined based on the accelerator pedal position, engine speed, primary pulley (input) speed, secondary pulley (output) speed, vehicle speed, input torque, stop lamp switch signal, transmission range switch signal, lock-up signal, power voltage, target shift ratio, oil temperature and oil pressure.

Secondary Pressure Feedback Control

In normal oil pressure control and oil pressure control in shifting, highly accurate secondary pressure is determined by detecting the secondary pressure using an oil pressure sensor and by feedback control.

Shift control

SHIFT CONTROL : System Description

SYSTEM DIAGRAM

DESCRIPTION

To select the gear ratio that can give the driving force to meet driver's intent or vehicle situation, the vehicle driving condition such as vehicle speed or accelerator pedal position is detected and the most appropriate gear ratio is selected and the shifting method before reaching the speed is determined. The information is output to the primary pressure solenoid valve to control the line pressure input/output to the primary pulley, to determine the primary pulley (movable pulley) position and to control the gear position.

D Position (OD ON) Gear shifting is performed in all shifting ranges from the lowest to the highest gear ratio.

D Position (OD OFF)

The gear ratio is generally high by limiting the shifting range on the high side, and this always generates a large driving power.

L Position

By limiting the shifting range only to the lowest of the gear ratio, a large driving force and engine brake are obtained.

Hill Climbing And Descending Control

If a downhill is detected with the accelerator pedal is released, the system performs downshift to increase the engine brake force so that vehicle may not be accelerated more than necessary. If a climbing hill is detected, the system improves the acceleration performance in re-acceleration by limiting the gear shift range on the high side.

NOTE:

For engine brake control on a downhill, the control can be stopped with CONSULT.

Control In Acceleration

From change of the vehicle speed or accelerator pedal position, the acceleration request level of the driver or driving scene is evaluated. In start or acceleration during driving, the gear shift characteristics with linearity of revolution increase and vehicle speed increase are gained to improve the acceleration feel.

Select control

SELECT CONTROL : System Description

SYSTEM DIAGRAM

DESCRIPTION

Based on accelerator pedal angle, engine speed, primary pulley speed, and the secondary pulley speed, the optimum operating pressure is set to reduce impact of a selector lever operation while shifting from “N” (“P”) to “D” (“R”) position.

Lock-up control

LOCK-UP CONTROL : System Description

SYSTEM DIAGRAM

DESCRIPTION

• Controls for improvement of the transmission efficiency by engaging the torque converter clutch in the torque converter and eliminating slip of the converter. Achieves comfortable driving with slip control of the torque converter clutch.
• The oil pressure feed circuit for the torque converter clutch piston chamber is connected to the torque converter clutch control valve. The torque converter clutch control valve is switched by the torque converter clutch solenoid valve with the signal from TCM. This controls the oil pressure circuit, which is supplied to the torque converter clutch piston chamber, to the release side or engagement side.
• If the CVT fluid temperature is low or the vehicle is in fail-safe mode due to malfunction, lock-up control is prohibited.

Lock-up engagement

In lock-up engagement, the torque converter clutch solenoid valve makes the torque converter clutch control valve locked up to generate the lock-up apply pressure. This pushes the torque converter clutch piston for engagement.

Lock-up release condition

In lock-up release, the torque converter clutch solenoid valve makes the torque converter clutch control valve non-locked up to drain the lock-up apply pressure. This does not engage the torque converter clutch piston.

IDLE NEUTRAL CONTROL

Idle neutral control

IDLE NEUTRAL CONTROL : System Description

SYSTEM DIAGRAM

DESCRIPTION

If a driver has no intention of starting the vehicle in D position, TCM operates the low brake solenoid valve and controls the oil pressure of the low brake to be low pressure. Therefore, the low brake is in the release (slip) status and the power transmission route of transaxle is the same status as the N position. In this way, the transaxle is in idling status and load to the engine can be reduced to improve fuel economy.

Idle Neutral Control Start Condition

Idle neutral control is started when all of the following conditions are fulfilled. However, during idle neutral control, idle neutral control is stopped when any of the following conditions is not met.

Driving environment : Flat road or road with mild gradient

Selector lever position : “D” position

Vehicle speed : 0 km/h (0 MPH)

Accelerator pedal position : 0.0/8

Brake pedal : Depressed

Engine speed : Idle speed

Turn signal lamp/hazard signal lamp : Not activated

NOTE:

Stops or prohibits the idle neutral control when the TCM and ECM detect that the vehicle is in one of the following conditions.

• Engine coolant temperature and CVT fluid temperature are the specified temperature or more, or the specified temperature or less.
• When a transaxle malfunction occurs.
• When the vehicle detects DTC and is in
• When idle speed increases due to heavy electric load*.

*: When any one of rear window defogger switch, A/C switch, headlamp, fog lamp is turned ON. In addition, when the steering wheel is operated.

Idle Neutral Control Resume Condition

When the idle neutral control finishes, if the vehicle is driven at more than the specified speed and the idle neutral control start conditions are satisfied, the idle neutral control starts again. If the vehicle has a malfunction, the idle neutral control does not start.

ECO MODE CONTROL

ECO MODE CONTROL : System Description

• Driving mode that selects the shift schedule with priority on fuel economy which gives low engine revolution
• The gear shift line is not changed with the control mode change for the following conditions:

• When the selector lever is at “L” position.
• When the selector lever is at D position and overdrive is OFF.

• For details on ECO mode control, refer to DMS-26, "ECO MODE CONTROL : System Description".

FAIL-SAFE

If a malfunction occurs in the system of CVT during ECO mode, the ECO mode indicator lamp turns OFF and the control switches to the normal mode control.

SPORT MODE CONTROL

SPORT MODE CONTROL : System Description

• Driving mode that keeps high engine revolution and provides direct feel and acceleration performance suitable for driving on winding road.
• The gear shift line is not changed with the control mode change for the following conditions:

• When the selector lever is at “L” position.
• When the selector lever is at D position and overdrive is OFF.

• For details on SPORT mode control, refer to DMS-63, "SPORT MODE CONTROL : System Description".

FAIL-SAFE

If a malfunction occurs in the system of CVT during SPORT mode, the SPORT mode indicator lamp turns OFF and the control switches to the normal mode control.

ON BOARD DIAGNOSTIC (OBD) SYSTEM

Description

This is an onboard diagnosis system which records diagnosis information related to the exhaust gases. It detects malfunctions related to sensors and actuators. The malfunctions are indicated by means of the malfunction indicator lamp (MIL) and are stored as DTC in the ECU memory. The diagnosis information can be checked using a diagnosis tool (GST: Generic Scan Tool).

Function of OBD

The GST is connected to the diagnosis connector on the vehicle and communicates with the on-board control units to perform diagnosis. The diagnosis connector is the same as for CONSULT. Refer to GI-47, "Description".

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