Diagnostic Strategy

Diagnostic Strategy
Diagnosis and testing an electronically controlled automatic transaxle is simplified by using the proven method of diagnosis. One of the most important things to remember is that there is a definite procedure to follow.

NOTE: Do not take short cuts or assume that critical checks or adjustments have already been made.

Follow the procedures as written to avoid missing critical components or steps.

Shift Solenoids
The shift solenoid assembly is located on the main control valve body and contains five solenoids used to control transaxle functions. Shift solenoids A and B control valves in the. main control valve body that control various up and down shifts. The coasting clutch solenoid controls operation of the coasting clutch, which provides engine braking when O/D is turned off.

Transmission Fluid Temperature, (TFT) Sensor
This sensor is part of the shift solenoid harness. The sensor is immersed in the transaxle fluid and is used by the TCM to help determine shift timing and feel. The sensor is a variable resistor, and the value of its resistance changes with temperature.

Electronic Pressure Control (EPC) Solenoid
The EPC solenoid controls the line pressure in the transaxle by operating the pressure regulator valve. The TCM will control the solenoid in order to match line pressure to current vehicle conditions and requirements.

Torque Converter Clutch (TCC) Solenoid
This solenoid is used in the transaxle control system to control the application, modulation and release of the torque converter clutch.

Vehicle Speed Sensor (VSS)
The VSS is a magnetic pickup that sends a signal to the TCM. The signal is based on vehicle speed and is used to help determine shift timing and feel.
To correctly diagnose a concern have the following publications available:
- Technical Service Bulletins (TSBs)
- Wiring Diagrams
Use the Diagnostic Flow Chart as a guide and follow the steps as indicated.

Preliminary Inspection
- Know and understand the customer's concern.
- Verify the concern by operating the vehicle.
- Check the fluid levels and condition.
- Check for non-factory add-on items.
- Check shift linkages for correct adjustment.
- Check TSBs regarding the concern.

Diagnostics
- Record all Diagnostic Trouble Codes (DTCs).
- Repair all non-transaxle codes first.
- Repair all transaxle codes second.
- Erase All continuous codes and attempt to repeat them.
- Repair all continuous codes.
- If only past codes are obtained, proceed to Diagnosis by Symptom Index for further information and diagnosis. Symptom Related Diagnostic Procedures
Follow the diagnostic sequence to diagnose and repair the concern the first time.