Diagnostic Strategy

Diagnostic Strategy
Troubleshooting an electronically controlled automatic transmission 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 any 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.
To correctly diagnose a concern have the following publications available:
^ Transmission Reference Manual.
^ Refer To Computers and Control Systems
^ TSBs.
^ Wiring Diagram.
These publications provide the information required when diagnosing transmission concerns.
Use the Diagnostic Flow Chart as a guide and follow the steps as indicated.

Preliminary Inspection
^ Know and understand the customers 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 proper adjustment.
^ Check TSBs regarding the concern.

Diagnostics
^ Carry out on-board diagnostic procedures key on engine off (KOEO) and key on engine running (KOER).
^ Record all diagnostic trouble codes (DTC's).
^ Repair all non-transmission codes first.
^ Repair all transmission codes second.
^ Erase all continuous codes and attempt to repeat them.
^ Repair all continuous codes.
^ If only pass codes are obtained, refer to Diagnosis By Symptom; 4R70W/4R75W - Automatic Transmission
Follow the diagnostic sequence to diagnose and repair the concern the first time.








Diagnostic Flow Chart