P0732 on GMC: How to Diagnose & Fix
Gear 2 Incorrect Ratio
1 GMC model · 1 documented issue · 1 critical · $1,800-$3,500 repair
P0732 on GMC by model: symptoms, diagnosis and fix
On GMT800 Sierra 1500 trucks equipped with the 4L60-E family automatic, a well-known internal failure is cracking or stripping of the reaction sun shell. Owners commonly report sudden loss of reverse, 2nd gear and 4th gear after a bang or flare, while 1st and 3rd still work. This is widely documented in transmission rebuild literature, repair databases, and owner reports for GM trucks and SUVs using this transmission.
Common Symptoms
- loss of reverse
- no 2nd gear
- no 4th gear
- harsh bang followed by missing gears
- shifts from 1st straight to 3rd
- slipping on acceleration
How to Fix
Diagnosis usually starts with verifying gear loss patterns, checking line pressure, and scanning for ratio/performance codes before condemning the unit. Repair requires transmission removal and overhaul or replacement, typically installing an upgraded hardened sun shell such as the commonly recommended 'Beast' style shell along with inspection of clutches, band, pump, and valve body wear items.
Sources for this issue (2)
P0732 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 P0732 mean on a GMC?
P0732 stands for "Gear 2 Incorrect Ratio." This code means the transmission control module detected that the gear ratio in 2nd gear does not match what it expects when the transmission is commanded into that gear. The computer compares input (turbine) speed to output shaft speed; if the math for 2nd gear is wrong, it sets this code. It usually points to internal slipping or a hydraulic/electronic control fault rather than a sensor reading error. On GMC it is documented across 1 model: Sierra 1500.
What are the most common causes of P0732?
The most common causes of P0732 are: Low or dirty/degraded transmission fluid, Worn or slipping friction element (clutch or band) that holds 2nd gear, Faulty shift solenoid, Valve body or pressure control problems, Internal mechanical wear or damage in the transmission, Clogged transmission filter restricting flow, Faulty input/output speed sensor giving skewed data. The specific cause varies by vehicle.
How much does it cost to fix P0732 on a GMC?
Published repair estimates on GMC range from $1,800 to $3,500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.