6HP26 Automatic Transmission

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 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:
^ Computers and Control Systems
^ Technical Service Bulletins (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 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 and OASIS messages 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 (DTCs).
^ 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, go to Diagnosis By Symptom. Diagnosis By Symptom

Follow the diagnostic sequence to diagnose and repair the concern the first time.