P0842: How to Diagnose & Fix — Transmission Fluid Pressure Sensor/Switch 'A' Circuit Low
2 vehicles · 2 makes · $300-$4,500 repair
How to diagnose and fix P0842: 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.
Chevrolet Silverado 1500 · 2007–2019
P0700 is not a specific fault by itself — it is an umbrella/MIL-request code the ECM stores whenever the transmission control module (TCM) detects an internal transmission problem and asks the ECM to turn on the check-engine light. On the Silverado 1500 it almost always appears alongside more specific companion codes, and the underlying failure follows two dominant, well-documented patterns depending on the transmission. On trucks with the 6L80 six-speed automatic (2007-onward 5.3L and 6.2L V8 models), the internal TEHCM (Transmission Electro-Hydraulic Control Module — GM's combined valve body, solenoids, pressure switches, and TCM in a single pan-mounted unit) develops internal circuit-board/solenoid faults from heat and fluid degradation, throwing P0700 together with codes like P0796, P0777, P0842, or P0973 and dropping the truck into limp mode. On older/base trucks with the 4L60E four-speed (4.3L/4.8L), the same P0700 is typically triggered by a failed shift solenoid (P0753/P0758) or a faulty internal mode switch. Because P0700 is a stored 'passenger' code, a scan tool that can talk to the TCM (not just a basic reader) is required to pull the specific sub-code that identifies the actual failed component.
Common Symptoms
- Check engine light on with P0700 stored
- Transmission stuck in limp mode / limited to one gear (often 3rd or 5th)
- Harsh or delayed shifts
- Transmission fails to shift or slips
- Torque converter clutch not locking up / shudder
- No movement or won't shift out of park in severe cases
How to Fix
Do NOT replace parts off the P0700 alone. Use a bidirectional/TCM-capable scan tool to read the companion codes stored in the transmission controller and verify transmission fluid level and condition first (low or burnt DEXRON-VI fluid alone can trigger the chain). For 6L80 trucks, a failed internal TEHCM is confirmed by multiple simultaneous solenoid/pressure codes; the fix is to drop the pan and replace the TEHCM, which MUST then be programmed to the vehicle's VIN with GM calibration files before the truck will start or shift correctly (ordering the OEM unit by the last 8 VIN digits can yield a plug-and-play unit needing no fast-adapt relearn). For 4L60E trucks, replace the specific failed shift solenoid or internal mode switch identified by the sub-code. Repair the wiring/connectors to the TCM if corrosion is found. On very new 2023-2025 Silverado 1500s, P0700 paired with P0747 is a known valve-body defect covered by Safety Recall N242454440 / Special Coverage N242454441 — check the VIN with a dealer for a free repair.
Sources for this issue (1)
GMC Acadia · 2007–2012
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)
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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?
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).
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?
Repair costs for P0842 range from $300 to $4,500, depending on the vehicle and root cause.
Which vehicles are affected by P0842?
Au7o has documented P0842 across 2 vehicle models from 2 manufacturers: Chevrolet, GMC.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.