ELECTRONIC CONTROL SYSTEM[LA4AX-EL (CD4E)]

• Shift timing, shift feel (line pressure) and TCC control in the automatic transaxle are controlled electronically by the PCM and its input/output network.

• The transaxle control is separate from the engine control strategy in the PCM, although some of the input signals are shared.

• Some input signals come from the engine-related sensors, MAF sensor, ECT sensor to give the PCM an idea of the load and climate in which the engine is operating under. Some other inputs are based on driver inputs, such as accelerator pedal position which is relayed to the PCM by the TP sensor. Still other inputs are provided by the transaxle itself, from sensors such as the TR switch (controlled by the placement of the selector lever) and the TFT sensor.

• Using all of these input signals, the PCM can determine when the time and conditions are right for a shift or TCC application. The PCM can also determine the line pressure needed to optimize shift feel. To accomplish these functions, the PCM controls five electronic solenoids, two on/off solenoids for shifting, one PWM solenoid for TCC control, an EPC solenoid for line pressure control, and a 3-2 T/CCS to control the release of the coast clutch and the coordinated release of the direct clutch and the apply of the low and intermediate band, during a 3-2 down-shift.

• The operation of the transaxle is controlled by the PCM. Many input sensors provide information to the PCM. The PCM sends the signals to the solenoids to control the transaxle.

• The PCM sends the signals to the solenoid valve body component (which is installed on the main control component) through the wiring harness to control the transaxle.

• The A/C cycling switch is located on the suction accumulator/drier.

• When the A/C cycling switch contact closes, the PCM receives a signal voltage from the A/C cycling switch to indicate that the magnet clutch is engaged.

• The PCM uses the A/C cycling switch signal to adjust line pressure to compensate for the additional engine load.

• The brake switch signals the PCM when the brakes are applied.

• The brake switch is closed when the brakes are depressed and open when they are released.

• The brake switch will also disengage TCC when the brakes are applied.

• The ECT detects the temperature of the engine coolant and supplies the information to the PCM.

• The PCM uses the ECT sensor to control TCC operation.

• The EI system consists of the PCM, a CKP sensor, and one multi-tower ignition coil.

• The CKP sensor sends a CKP signal to the PCM. The PCM then sends the appropriate ignition signal to the ignition coil. The PCM uses this signal in the transaxle shift strategy, as well as TCC control and line pressure control.

• Wide open throttle (WOT) shift control is also affected by the EI system input.

• The MAF sensor directly measures the mass of the air flowing into the engine.

• The MAF sensor output is a D.C. (analog) signal ranging from 0.5—5.0 V used by the PCM to calculate the injector pulse width for air/fuel ratio.

• For transaxle strategies, the MAF sensor is used for EPC, shift and TCC scheduling.

• The O/D OFF switch is a momentary contact switch.

• When the O/D OFF switch is pressed, a signal is sent to the PCM. The PCM energizes the O/D OFF indicator light and engages or disengages 4th gear operation and provides coast braking in 2nd gear and 3rd gear.

• The O/D OFF indicator light is located in the instrument cluster and is labeled O/D OFF.

• The O/D OFF switch controls the on/off operation of the O/D OFF indicator light.

• When the driver initially presses the O/D OFF switch, the O/D OFF indicator light turns ON to indicate that transaxle operation in 4th gear is disabled. When the driver presses the O/D OFF switch again, the O/D OFF indicator light turns off.

• The TP sensor is a potentiometer mounted on the throttle body.

• The TP sensor detects the position of the throttle plate and sends this information to the PCM as a varying voltage signal.

• If a fault occurs in the TP sensor circuit, the PCM will recognize that the TP sensor signal is out of specification. The PCM will then operate the transaxle at a high EPC pressure to prevent transaxle damage. The PCM also uses this signal for shift scheduling, EPC and TCC control.

• The TFT sensor is located on the solenoid valve body. It is a temperature-sensitive device called a thermistor.

• The resistance value of the TFT sensor will vary with ATF temperature.

• The PCM monitors the voltage across the TFT sensor to determine the temperature of the ATF. The PCM uses this signal to determine shift scheduling and to control line pressure for cold and hot temperature operation. The PCM also inhibits TCC operation at low transaxle temperature and adjusts EPC pressures.

• The TR switch incorporates a series of step down resistors which act as a voltage divider.

• The PCM monitors this voltage which corresponds to the position of the selector lever (P, R, N, D, 2, 1) to determine desired gear and EPC pressure.

• The TR switch is located on the top of the transaxle, and also contains the neutral/start and back-up light circuits.

• The TSS sensor is a magnetic pick-up that sends a signal to the PCM that indicates turbine shaft input speed.

• The TSS sensor provides the TSS information for TCC control strategy. Also used in determining EPC pressure setting during shifts.

• The OSS sensor is a magnetic pick-up which detects the park gear teeth rotation and sends a signal to the PCM as an indicator of the transaxle output shaft speed.

• The OSS signal is processed by the PCM for shift scheduling and inputs to other control modules such as: Electronic Speedometer, Trip Computer, Speed Control, Adaptive Damping, Auxiliary Warning and Radio CD.

• The solenoid valve body component contains the TFT sensor, as well as five PCM controlled output devices:

• The connector from the solenoid valve body component is located on top of the transaxle case, where connected to the PCM wiring harness.

• If the any components of the solenoid valve body component need replacement, replace the solenoid valve body as a single unit.

*3 :When a manual pull-in occurs above a calibrated speed, the transaxle will not down-shift from the higher gear until the vehicle speed drops below this calibrated speed

• The EPC solenoid is a VFS solenoid.

• The VFS solenoid is an electro-hydraulic actuator combining a solenoid and a regulating valve. This solenoid provides EPC which regulates LP and LM pressure. This is controlled by producing a resisting pressure to the main regulator and LM circuits. The LP and LM pressures control the clutch application pressures.

• The TCC solenoid is a PWM style solenoid.

• The PWM solenoid is used to control the apply and release of the bypass clutch in the torque converter.

• By modulating the pulse width of the TCC solenoid the pressure in the S4 circuit varies modulating the apply and release of the bypass clutch in the torque converter.

• The 3-2 T/CCS is a VFS solenoid.

• The VFS solenoid is an electro-hydraulic actuator combining a solenoid and a regulating valve. It supplies pressure to the S3 circuit to control the release of the direct clutch and to apply the intermediate and overdrive band during a 3-2 down-shift. This solenoid also regulates the pressure in the S3 circuit to control the application and release of the coast clutch.

• Shift solenoids A and B provide gear selection of 1st gear through 4th gear by providing on/off pressure control to the shift valves.

Position/range	PCM Commanded Gear	SSA	SSB	3-2T/CCS	TCC
P/N	—	OFF	ON	ON	OFF
R	—	OFF	ON/OFF	ON	^*1
D (Normal mode)	1	ON	ON	ON	^*1
2	OFF	ON	ON	^*2
3	OFF	OFF	ON	^*2
4	ON	OFF	ON	^*2
D (O/D OFF mode)	1	ON	ON	ON	^*1
2	OFF	ON	OFF	^*2
3	OFF	OFF	OFF	^*2
2	2	OFF	ON	OFF	^*2
2^*3	3	OFF	OFF	OFF	^*2
1	1	ON	ON	OFF	^*1
1^*2	2	OFF	ON	OFF	^*2
1^*3	3	OFF	OFF	OFF	^*2