P0729 on Chevrolet
Gear 6 Incorrect Ratio
P0729 on Chevrolet vehicles indicates gear 6 incorrect ratio. Au7o has documented this code across 2 Chevrolet models — most commonly on Cruze, Silverado 1500. 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. Typical repair costs on Chevrolet range from $1,500 to $4,000, depending on the specific model and root cause.
Common 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
- •Failing torque converter
- •Internal mechanical wear or damage
- •Speed sensor fault giving incorrect ratio calculation
P0729 on Chevrolet by Model
Chevrolet Cruze(1 issue)
- 6T40 3-5-Reverse Wave Plate Fracture - Sudden Loss of 3rd, 5th and Reverse2011-2013
The early (Gen 1) 6T40/6T30 automatic uses a stamped steel wave plate in the 3-5-Reverse clutch pack. On 2011-2012 builds the plate cracks and shatters without warning, instantly wiping out 3rd gear, 5th gear and reverse. The car will usually still move in 1st, 2nd, 4th and 6th, so drivers often describe it as 'it flared, then it won't back up.' Debris from the shattered plate circulates through the valve body and contaminates the whole unit. This is distinct from the well-known torque-converter shudder - it is a hard mechanical failure, not a driveability complaint. GM revised the wave plate in later 6T40 builds and the failure rate drops sharply on 2013+ cars.
Chevrolet Silverado 1500(1 issue)
- 4L60E Automatic Transmission 3-4 Clutch Pack and Sun Shell Failure (Slipping, Loss of 3rd/4th Gear)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.
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View P0729 across all makes →Frequently Asked Questions
What does P0729 mean on Chevrolet?▼
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 Chevrolet specifically, this code is documented across 2 models.
What causes P0729 on Chevrolet vehicles?▼
Common causes on Chevrolet: 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. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0729 on a Chevrolet?▼
Repair costs on Chevrolet range from $1,500 to $4,000, depending on the specific model and root cause.
Which Chevrolet models have P0729 documented?▼
Au7o has documented P0729 on 2 Chevrolet models: Cruze, Silverado 1500.