General Description

GENERAL DESCRIPTION
The NAG1 electronic transmission is an electronically controlled five speed transmission with a controlled slip torque converter. The NAG1 electronic transmission is a conventional transmission in that it uses hydraulically applied clutches to shift a planetary gear train. However, the electronic control system replaces many of the mechanical and hydraulic components used in conventional transmission valve bodies.

The ratios for the gear stages are obtained by 3 planetary gear sets. Fifth Gear is designed as an Overdrive with a high speed ratio. The gears are actuated electronically/hydraulically. The electronic control system enables precise adaptation of pressures to the respective operating conditions and to the engine output during a shift phase, which results in a significant improvement in shift quality.

FUNCTIONAL OPERATION
The NAG1 electronic transmission has a fully adaptive control system. The system performs its functions based on continuous real time sensor and switch feedback information. In addition the TCM receives information from the Shift Lever Assembly, ECM (engine management) and ABS (chassis systems) controllers over the CAN bus. The CAN bus is a high speed communication bus that allows real time control capability between various controllers. Most messages are sent every 20 milliseconds, this means critical information can be shared between the Transmission, Shifter, Engine and ABS controllers. The CAN bus is a two wire bus with a CAN C Bus (+) circuit and a CAN C Bus ( ) circuit. The CAN bus uses a twisted pair of wires in the harness to reduce the potential of radio and noise interference. The CAN bus also uses a 120 ohm terminating resistor in both the ECM and Sentry Key Remote Entry Module (SKREEM) modules. The module terminating resistance is measured across both CAN bus circuits at the ECM or SKREEM module.

The control system automatically adapts to changes in engine performance, vehicle speed, and transmission temperature variations to provide consistent shift quality. The control system ensures that clutch operation during upshifting and downshifting is more responsive without increased harshness. The TCM controls the actuation of solenoid valves for modulating shift pressure and gear change. The required pressure level is calculated from the load condition, engine speed. Power for the transmission system is supplied through the Transmission Relay. The TCM is located in the under the drivers seat of the vehicle.

The Transmission Control Module (TCM) continuously checks for electrical problems, mechanical problems, and some hydraulic problems. When a problem is sensed, the TCM stores a Diagnostic Trouble Code (DTC). Some of these codes cause the transmission to go into limp in or default mode.

The NAG1 will default in the current gear position if a DTC is detected, then after a key cycle or shift to park the transmission will go into Limp in, which is mechanical 2nd gear. Some DTC's may allow the transmission to resume normal operation (recover) if the detected problem goes away. Permanent limp in DTC will recover when the key is cycled, but if the same DTC is detected for three key cycles the system will not recover and the DTC must be cleared from the TCM with the DRBIII scan tool.

Once the DRBIII is in the Transmission portion of the diagnostic program, it constantly monitors the TCM to see if the system is in limp in mode. If the transmission is in limp in mode, the DRBIII will flash the red LED.

CONTROLLER MODES OF OPERATION

Permanent limp in mode
When the TCM determines there is a nonrecoverable condition present that will not allow proper transmission operation, it will place the transmission in permanent limp in mode. When the condition occurs the TCM will turn off all solenoids as well as the solenoid supply output circuit. If this occurs while the vehicle is moving, the transmission will remain in the current gear until the ignition is turned off or shifter is placed in the P position. Once the shifter has been placed in P the Transmission will only allow 2nd gear operation. If the problem occurs while the vehicle is not moving the transmission will only allow 2nd gear operation.

Temporary limp in mode
This mode is the same as the permanent limp in mode except if the condition is no longer present the system will resume normal operation. (Recoverable DTC)

Undervoltage limp in mode
When the TCM detects that system voltage has dropped below 8.5 volts it will disable voltage dependant diagnostics and place the transmission in the temporary limp in mode. When the TCM senses that the voltage has risen above 9.0 volts, normal transmission operation will be resumed.

Hardware Error Mode
When the TCM detects a major internal error the transmission will be placed in the permanent limp in mode and cease all communication over the CAN bus. Once the TCM has entered this mode normal transmission operation will not resume until all DTC's are cleared from the TCM.

Loss of Drive
If the TCM detects a situation that has resulted or may result in engine or transmission failure, the transmission will be placed in the neutral position.

Improper Ratio, Input Sensor Overspeed, or Engine Overspeed DTC's will cause the loss of drive.

Controlled Limp in Mode
When a failure condition does not require the TCM to shut down the solenoid supply, but the failure is of a degree where the TCM will place the transmission into a predefined gear, there will be several shift performance issues. Examples of this are, with the transmission slipping the controller will attempt to place the transmission into third gear and maintain third gear for all forward drive conditions. Another example is some of the CAN bus message issues if the TCM does not receive required information from the Engine Controller, then default values are used which may result in poor transmission shift performance.

MIL ILLUMINATION
For failures detected by the Transmission Controller that result in the controller placing the transmission into a limp in mode, except for System Overvoltage and System Undervoltage DTCs, the MIL will be illuminated. The Transmission Control Module will inform the ECM over the CAN bus that a failure has occurred. The ECM will illuminate the MIL. If the condition is removed and the failure becomes Stored Intermittent), the Transmission controller will stop reporting that the DTC is active and the ECM will extinguish the MIL.

NOTE: The MIL will light when the problem is first detected and it will not go off until the next ignition cycle, after all problem conditions have been checked for their presence. This normally takes several minutes of driving.

SOLENOIDS

1-2/4-5 solenoid
The 1 2/4 5 solenoid is activated when the TCM determines that the transmission must shift into or out of 2nd gear or 5th gear. The solenoid is only activated during the shifting of the transmission. When the solenoid is activated, hydraulic pressure is applied to the proper shift elements in the transmission to allow the desired shift. Once the shift is completed, the solenoid is turned off.

2-3 solenoid
The 2-3 solenoid is activated when the TCM determines that the transmission must shift into or out of 3rd gear. The solenoid is only activated during the shifting of the transmission. When the solenoid is activated hydraulic pressure is applied to the proper shift elements in the transmission to allow the desired shift. Once the shift is completed, the solenoid is turned off.

3-4 solenoid
The 3-4 solenoid is activated when the TCM determines that the transmission must shift into or out of 4th gear. The solenoid is only activated during the shifting of the transmission. When the solenoid is activated, hydraulic pressure is applied to the proper shift elements in the transmission to allow the desired shift. Once the shift is completed, the solenoid is turned off.

TCC solenoid
The TCC solenoid is activated when the TCM determines that the Torque converter clutch should be activated. The TCC clutch is a variable slip torque clutch that allows control of torque converter slip from 5% to 95.5% of full TCC engagement. The clutch is controlled by the TCC solenoid which is Pulse Width Modulated (PWM) to provide the desired amount of slip.

Shift Pressure Solenoid
The Shift Pressure Solenoid is activated when the TCM determines that a transmission shift is required. The solenoid is PWM controller to allow the proper amount of hydraulic pressure to the shift elements. The solenoid is only activated during the shifting of the transmission. When the solenoid is activated, hydraulic pressure is removed from the proper shift elements to allow the desired shift. Once the shift is completed, the solenoid is turned off.

Modulation pressure solenoid
The modulation pressure is always active. The solenoid is Pulse Width Modulated (PWM) controlled and is used to modulate the hydraulic system pressure to the desired pressure.

TRANSMISSION COMPONENT DESCRIPTIONS

Shift Assembly
The Shift Lever Selector transmits all selector lever positions, as well as selected shift ranges to the TCM over the CAN Bus. At the same time, the selector lever positions P. R. N. and D are transmitted by a cable to the selector lever shaft in the transmission.

Brake shift inter lock
To prevent unauthorized shifting out of the park position, the Selector lever is locked in the Park position until the ignition key is turned to the run position and the brake pedal is pressed. This will allow the driver to shift out of the park position.

Reverse Lamp Output
The Reverse Light Switch is integrated into the shifter module and controls the reverse lights.

Reverse Inhibitor
The Shift Lever Assembly constantly monitors ABS wheel speed to prevents an inadvertent selection of rearm at speeds above approximately 6.4 Km/h (4MPH). The Reverse inhibitor is part of the Shift Lever Assembly and is controlled by the Shift Lever Assembly module.

Trans temp sensor P/N Switch circuit
The TCM will detect the selector lever in park and neutral positions. The TCM does this by monitoring the Transmission temperature sensor signal along with the shifter position signals. The P/N switch contact is operated by a cam located in the transmission which, opens a reed contact switch that is wired in series with the transmission temperature sensor. When the P/N contact switch is opened in park and neutral, the TCM senses a high transmission temperature. Confirming the P/N switch status. Note: In park or neutral, the TCM uses engine temperature (to avoid setting a DTC). The TCM sends a hardwired signal to the ECM that will allow the ECM controlled start circuit to engage in P or N only. The TCM also sends a P/N bus message to the ECM to confirm the P/N switch status.

The Normal Transmission Temperature Sensor resistance is between 500.0 and 2500.0 ohms. The normal voltage limits for the transmission temperature sensor, are between 0.5 and 3.0 volts.

Input Speed Sensors
The NAG1 transmission has two input speed sensors N2 and N3, both speed sensors are located on the valve body and report DTC's for the input speed sensors errors. The speed sensors are Hall Effect speed sensors that are used by the TCM to calculate the transmissions input speed. Since the input speed could not be measured directly, two of the drive elements are measured. Two input speed sensors were required because both drive elements are not active in all gears. The input sensors N2 and N3 will report the same input speed in gears 2nd, 3rd or 4th. If the N2 and N3 input speed signals are not the same in these gears then there is an issue with the transmission and the DTC Input Sensors Mismatch will be set.

The N3 input speed is not reported in 1st and 5th gears. The N2 sensor is not reported in Reverse. The Input Speed Sensor Overspeed is a rationality check that is intended to indicate a major transmission failure and will cause a loss of drive (place the transmission in Neutral)

Output Speed Sensor (ABS signal)
The NAG1 transmission does not have an output shaft speed sensor. The TCM uses the ABS (Antilock Brake System) Wheel Speed sensor information, it receives over the CAN bus, to calculate the transmissions output shaft speed. The TCM monitors the ABS system for functionality and reports ABS speed sensor and communication DTCs, which will affect proper transmission operation.