P0729 on Infiniti: How to Diagnose & Fix
Gear 6 Incorrect Ratio
1 Infiniti model · 1 documented issue
On Infiniti vehicles, P0729 (gear 6 incorrect ratio) is most often reported on the 2009-2013 Infiniti G37 as 7-Speed Automatic (RE7R01A) Harsh 2-1 Downshift, Gear Hunting and Ratio DTCs Requiring TCM/ECM Reflash ($0-$250 repair). Have an Infiniti dealer apply the latest TCM/ECM reprogram (bulletin family ITB10-075 / ITB12-027 and later revisions) with CONSULT-III; many owners report the harsh 2-1 downshift and hunting are cured or greatly reduced. If ratio codes persist after the reflash, the dealer flow is to inspect fluid level/condition and replace the valve body or torque converter. Each section below gives the symptoms, how to confirm the cause, the fix, parts and sources for that model.
Common causes of P0729 (all vehicles)
- Low or contaminated transmission fluid
- Worn or slipping clutches/bands inside the transmission
- Faulty shift solenoid or pressure control solenoid
- Valve body wear or sticking valves
- Failing torque converter
- Internal mechanical wear or damage
- Speed sensor fault giving incorrect ratio calculation
P0729 on Infiniti by model: symptoms, diagnosis and fix
The 7-speed automatic introduced for the 2009 G37 developed a widely reported drivability complaint: a hard clunk on the 2nd-to-1st downshift when coasting to a stop, gear hunting/searching under light throttle, delayed or harsh upshifts when cold, and in some cases stored incorrect-gear-ratio codes. The MyG37 '7-speed transmission reprogram' thread runs well past 170 pages of owner reports. Infiniti responded with a series of TCM/ECM reprogramming bulletins (owners cite ITB10-075 and later ITB12-027 revisions) rather than hardware replacement; only a minority of cars needed a torque converter or valve body.
Common Symptoms
- Hard clunk or jerk on the 2-1 downshift when stopping
- Transmission hunts between gears at light throttle
- Delayed or harsh shifts when cold
- Check engine light with gear-ratio codes
How to Fix
Have an Infiniti dealer apply the latest TCM/ECM reprogram (bulletin family ITB10-075 / ITB12-027 and later revisions) with CONSULT-III; many owners report the harsh 2-1 downshift and hunting are cured or greatly reduced. If ratio codes persist after the reflash, the dealer flow is to inspect fluid level/condition and replace the valve body or torque converter. No recall; reflash was covered under powertrain warranty and is a nominal-cost labor item out of warranty.
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View P0729 across all makes →Frequently asked questions
What does P0729 mean on a Infiniti?
P0729 stands for "Gear 6 Incorrect Ratio." P0729 means the transmission control system detected an incorrect gear ratio in 6th gear — the computer compares input shaft speed to output shaft speed and found the resulting ratio doesn't match what 6th gear should produce. This usually indicates the transmission is slipping in that gear, a clutch or band isn't holding, or a hydraulic/solenoid control problem is preventing proper engagement. You may feel slipping, flaring RPM, harsh shifts, or the transmission dropping into limp mode. Low fluid and worn internal components are frequent contributors. On Infiniti it is documented across 1 model: G37.
How do I diagnose P0729 on a Infiniti G37?
Have an Infiniti dealer apply the latest TCM/ECM reprogram (bulletin family ITB10-075 / ITB12-027 and later revisions) with CONSULT-III; many owners report the harsh 2-1 downshift and hunting are cured or greatly reduced. If ratio codes persist after the reflash, the dealer flow is to inspect fluid level/condition and replace the valve body or torque converter. No recall; reflash was covered under powertrain warranty and is a nominal-cost labor item out of warranty. Published repair guidance and available estimates are in the G37 section on this page.
What causes P0729 on Infiniti vehicles?
Documented causes on Infiniti: 7-Speed Automatic (RE7R01A) Harsh 2-1 Downshift, Gear Hunting and Ratio DTCs Requiring TCM/ECM Reflash. Generic causes of P0729: Low or contaminated transmission fluid, Worn or slipping clutches/bands inside the transmission, Faulty shift solenoid or pressure control solenoid, Valve body wear or sticking valves.
How much does it cost to fix P0729 on a Infiniti?
Repair costs vary widely with the root cause and Infiniti model; each issue on this page carries its own estimate where one is published.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.