2010 Infiniti FX35 P0729 Gear 6 Ratio Incorrect - Transmission Shifting Issues
Over the past few months, my 2010 Infiniti FX35 has experienced sudden loss of power while driving twice. Three days ago, the check engine light came on and displayed 'Service Engine Soon'. After connecting an OBD-II scanner today, I received a diagnostic code P0729: "Gear 6 Incorrect Ratio". As a test, I switched to manual mode and observed perfect shifting all the way from gear seven down to first. On both automatic and manual drives during highway trips, the transmission shifts smoothly without any issues. I have no other diagnostic codes, and my transmission was flushed approximately two years ago — with about 30,000 miles since then. I'm looking for advice on what could be causing this P0729 error and how to resolve it. Any insights or troubleshooting steps would be greatly appreciated.
P0729 - Description: This fault is triggered when the automatic transmission fails to shift into gear 6 as instructed by the Transmission Control Module (TCM). The issue can stem from both electrical problems (such as open or shorted circuits) and mechanical faults, including a sticking control valve or improper solenoid operation. Recommended troubleshooting steps: Use CONSULT-III or a Nissan-specific scan tool to perform an extensive trouble tree analysis. Additionally, please confirm if any other diagnostic codes are present — transmission service history is also important for context.