P0729 on Acura: How to Diagnose & Fix
Gear 6 Incorrect Ratio
1 Acura model · 1 documented issue · 1 critical
P0729 on Acura by model: symptoms, diagnosis and fix
The ZF 9HP 9-speed automatic introduced on the 2016 MDX suffers from documented hesitation, harsh shifts, lurching, and unexpected downshifts/deceleration. Drivers report the vehicle hesitating from a stop, banging into gear, or briefly losing power. Software miscommunication between TCM, ECM and throttle control is the alleged root cause; a class action was filed alleging Honda knew of the defect from 2015.
Common Symptoms
- Hesitation from a stop
- Hard or banging shifts
- Unexpected downshift while cruising
- Brief loss of power
- Lurching at low speed
How to Fix
Have dealer apply latest TCM/PGM-FI software updates first (covered by powertrain warranty). If symptoms persist, request fluid replacement and dealer escalation; document everything for lemon-law/class-action relief. Avoid jerky throttle inputs while cold.
Sources for this issue (3)
P0729 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0729 mean on a Acura?
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 Acura it is documented across 1 model: MDX.
What are the most common causes of P0729?
The most common causes of P0729 are: 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. The specific cause varies by vehicle.
How much does it cost to fix P0729 on a Acura?
Repair costs vary widely with the root cause and Acura model; each issue on this page carries its own estimate where one is published.
Looking for P0729 on a different make?
View P0729 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.