P0842 on GMC: How to Diagnose & Fix
Transmission Fluid Pressure Sensor/Switch 'A' Circuit Low
1 GMC model · 1 documented issue · 1 critical · $1,800-$4,500 repair
P0842 on GMC by model: symptoms, diagnosis and fix
The 35R clutch wave plate inside the 6T70/6T75 six-speed transaxle cracks and fractures, allowing the 35R clutch piston to overstroke and leak apply pressure. The result is a hard flare or slip in 3rd and 5th gear and eventually a complete loss of reverse. Failures typically begin after about 25,000 miles and are extremely common on the early Lambda Acadia; GM eventually extended coverage on the wave plate to 10 years/120,000 miles. Debris from the broken plate circulates through the transmission, so a simple plate swap is often not enough on high-mileage units.
Common Symptoms
- No reverse gear
- Slip or flare shifting into 3rd gear
- Harsh or delayed 3-5 shifts
- Check engine / SES light on
- RPM flares under acceleration then catches
How to Fix
Transmission must come apart. The correct repair is replacement of the 35R clutch wave plate with the redesigned/updated part plus new 35R clutch pack and seals, a thorough flush of the cooler and valve body, and a fluid/filter change. On units run for a long time after failure, a full rebuild or remanufactured transaxle is the realistic fix. Check eligibility under the extended special coverage before paying out of pocket.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Sonnax 3-5-Reverse Drum Saver Kit (upgraded wave plate + cupped steel)Cross-refSonnax 124555K$55–$120
Fits Gen.1 and Gen.2 6T70/6T75 — the 2007-2012 Ac
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Sources for this issue (3)
P0842 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 P0842 mean on a GMC?
P0842 stands for "Transmission Fluid Pressure Sensor/Switch 'A' Circuit Low." The transmission fluid pressure sensor/switch 'A' circuit voltage is below the expected range (too low / shorted to ground). On GMC it is documented across 1 model: Acadia.
What are the most common causes of P0842?
The most common causes of P0842 are: Sensor signal shorted to ground, Faulty pressure sensor/switch A, Corroded/damaged connector, Internal TCM fault. The specific cause varies by vehicle.
How much does it cost to fix P0842 on a GMC?
Published repair estimates on GMC range from $1,800 to $4,500 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.
Looking for P0842 on a different make?
View P0842 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.