Problem: After the rear main oil seal was replaced, the MIL was on with DTCs: P0721 and P0731 present.
P0721 – OUTPUT SPEED SENSOR CIRCUIT PERFORMANCE
P0731 – GEAR RATIO ERROR IN 1ST
Details: These DTCs were not present before the repair. The shop checked all electrical connectors for being disconnected, pins pushed back or the harness being pinched. Everything looked good so before they started diving into a lengthy diagnosis, they called Tech-Assist for some advice.
Because this issue happened right after the transmission was removed, the Tech-Assist consultant suggested double checking the harness connectors for being swapped.
NOTE: They can have the same connector shapes and pin configurations.
Confirmed Repair: Sure enough, the connectors were swapped. The tech reinstalled the connectors in the correct positions and cleared the DTCs. After the test drive, the DTCs did not return. Fixed!