P0729: How to Diagnose & Fix — Gear 6 Incorrect Ratio
11 vehicles · 7 makes · $150-$6,500 repair
How to diagnose and fix P0729: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Ford Fiesta · 2011–2019
The Ford Fiesta equipped with the DPS6 PowerShift dual-clutch automatic transmission is one of the most complained-about vehicles in recent history. The dry dual-clutch design causes severe shuddering, jerking, hesitation, and complete loss of power during acceleration. The clutch plates overheat and wear prematurely, often before 50,000 miles. The Transmission Control Module (TCM) software frequently fails to adapt properly, causing delayed shifts, harsh engagement, and rollback on hills. Ford faced a class-action lawsuit involving nearly 1.5 million vehicles and a federal settlement was reached.
Common Symptoms
- Violent shuddering or bucking during acceleration from a stop
- Transmission slipping and RPMs flaring without acceleration
- Harsh or jerky shifts between 1st and 2nd gear
- Hesitation or delayed engagement when pressing the gas pedal
- Vehicle rolls backward on hills even with foot on gas
- Grinding or chattering noise from transmission area
- Wrench warning light or transmission malfunction message
How to Fix
Check if your vehicle is covered under Ford's extended warranty or class-action settlement — many Fiestas qualify for free clutch and TCM replacement. If out of warranty, have the clutch assembly and TCM reprogrammed or replaced ($1,500-$3,500). Some owners have had success with multiple TCM reflashes to improve shift quality. As a last resort, some owners have converted to a manual transmission. Avoid the PowerShift entirely when purchasing a used Fiesta — manual transmission models are far more reliable.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Transmission Clutch KitCross-refK70564-01
Fitment confirmed against the ShowMeTheParts catalog for this vehicle's year and engine.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (2)
Chevrolet Silverado 1500 · 1994–2010
The 4L60E 4-speed automatic behind the half-ton Silverado is notorious for wearing out its 3-4 clutch pack and cracking the input 'sun shell' (reaction sun gear shell) as mileage climbs. Owners report the truck suddenly loses 3rd and 4th gear (revs up but won't pull) while reverse and low gears still work, or a hard grinding/no-move with a fractured sun shell. The 3-4 clutch is the known weak point and often burns up first; the larger input drum on 2004-and-up units also likes to crack internally. This is one of the single most-searched failures for these trucks.
Common Symptoms
- Engine revs but truck won't accelerate in 3rd/4th (slipping)
- Sudden loss of 3rd and 4th gear, still has 1st/2nd/reverse
- Harsh or delayed 1-2 / 2-3 shifts
- Grinding or clunk then no forward movement (broken sun shell)
- Burnt-smelling, dark transmission fluid
- Check engine light with transmission codes
How to Fix
Confirm with a scan for gear-ratio/slip codes and a pressure test before condemning the unit. Fix is a transmission rebuild or reman: replace the 3-4 clutch pack, install a hardened 4L60E sun shell (aftermarket beast/heavy-duty shell over the stamped OEM piece), fresh bands/steels, and rebuild or replace the valve body. Adding an auxiliary transmission cooler and shortening fluid-change intervals to ~30k miles greatly extends life. Reman units are widely available; a full-service rebuild with upgraded shell is the durable fix.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Hardened 4L60E reaction sun shell ("sun shell") kit — Sonnax SmartShellOEM24228345Cross-refSonnax 77749-02K (SmartShell heavy-duty reaction shell kit), Sonnax 7774902K (RockAuto/Amazon listing form of same part), Transmission Parts Distributors S74624SS$140–$210
The stamped OEM sun shell (ACDelco 24228345) is the part that cracks/strips; every rebuild should replace it with a hardened aftermarket shell. Sonnax 77749-02K is the current SmartShell kit (shell + enclosed thrust bearing + custom roll…
- 4L60E 3-4 clutch pack (heavy-duty 9-friction "Power Pack") — AltoCross-refAlto 057757B (OE-style tan frictions, 9 frictions/10 steels,, Alto 057757C / 57757C (High Energy carbon-metallic 9-clutch , Alto 057757A / A74100GK (Red Eagle Power Pack with HP pressu$60–$135
The 3-4 clutch is the pack that burns up and takes 3rd/4th gear with it. Alto's 3-4 Power Pack replaces the stock frictions/steels/pressure plate with 9 frictions in the same input-drum space (~50% more friction area).
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (1)
Lincoln Aviator · 2020–2023
Some 2020-2023 Lincoln Aviators equipped with a 10R60 and built on or before December 23, 2022, or a 10R80 MHT and built on or before August 15, 2022, may have harsh or delayed engagement and/or harsh or delayed shifts. Ford TSB 22-2428 says the condition may involve PCM/TCM software, the transmission solenoid-ID strategy, sticking main-control valves, or axial movement of the CDF clutch-cylinder sleeve. The complaint may occur with or without a malfunction indicator and the bulletin's listed transmission DTCs. The symptom alone does not select a valve body, CDF cylinder, or complete transmission.
Common Symptoms
- Harsh engagement
- Delayed engagement
- Harsh shift
- Delayed shift
- Malfunction indicator with a bulletin-listed transmission DTC
How to Fix
Have a Ford/Lincoln-capable technician confirm the transmission and build date, retrieve PCM/TCM faults, and follow TSB 22-2428 in order. The bulletin begins with available PCM/TCM programming and an adaptive-learning drive cycle, then uses the stored faults and clutch behavior to select an accelerated main-control break-in routine. If the condition remains, the procedure can require main-control overhaul and, only after the bulletin's later tests fail, condition-specific internal transmission repair. Parts and coverage must be selected by VIN and the actual failed step; this record intentionally has no buy link.
Owner tips & cautions
- TipRecord the exact shift or engagement event and ask for the PCM/TCM fault report plus the TSB decision-tree step that failed before approving internal transmission work.
- WarningDo not order a valve body or CDF part from harsh shifting alone; Ford's procedure can resolve the condition through programming, adaptive learning, or clutch cycling before parts are selected.
Sources for this issue (1)
Acura MDX · 2016–2019
Infiniti G37 · 2009–2013
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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?
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.
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?
Repair costs for P0729 range from $150 to $6,500, depending on the vehicle and root cause.
Which vehicles are affected by P0729?
Au7o has documented P0729 across 11 vehicle models from 7 manufacturers: Acura, Chevrolet, Ford, Infiniti, Lincoln, Nissan, Volkswagen.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.