P0842 on Subaru: How to Diagnose & Fix
Transmission Fluid Pressure Sensor/Switch 'A' Circuit Low
1 Subaru model · 1 documented issue · 1 critical
P0842 on Subaru by model: symptoms, diagnosis and fix
On the 2019 Ascent the mid-joint of the transmission hydraulic pressure sensor harness was built with dissimilar metals - tinplate against copper. Galvanic action forms an oxide film at that joint, and the film corrupts the pressure signal the sensor sends to the TCU. When the sensor reports a pressure HIGHER than actual, the TCU commands the valve to reduce line pressure, and the Lineartronic's drive chain loses clamping tension. Slipping chain produces noise, vibration and hesitation, and continued driving in that state leads to loss of power. Recall population was 76,842 vehicles. This is a separate campaign and a separate root cause from the later TR690 chain-guide/TCU-programming recall (21V955 / WRK-21) - that one is a programming issue at clutch engagement, this one is a corroded sensor harness.
Common Symptoms
- Irregular noise from the transmission
- Vibration while driving
- Hesitation under acceleration
- Malfunction indicator lamp illuminated
- Loss of power if driven in the slipping condition
How to Fix
Free recall remedy under NHTSA 19V855 / Subaru campaign WUV-07. The base remedy is a TCU reprogram with more robust pressure-variation compensation. Vehicles found with specific stored diagnostic trouble codes also get the hydraulic sensor harness replaced. Any vehicle confirmed to have already run with low drive-chain tension gets a complete transmission assembly replacement, all at no charge. Because chain damage is cumulative, get the campaign done before symptoms appear - once the chain has slipped, a reprogram alone will not restore it.
Sources for this issue (4)
- NHTSA Part 573 Safety Recall Report 19V-855 (Subaru Ascent transmission hydraulic sensor)article
- Subaru Product Campaign Bulletin WUV-07 (recall 19V-855)article
- Safety Recall WUV-07 - CVT Chain Slip - 2019 Subaru Ascentarticle
- Subaru Ascent, Legacy, and Outback Recalled for Transmission Failure - Consumer Reportsarticle
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 Subaru?
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 Subaru it is documented across 1 model: Ascent.
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 Subaru?
Repair costs vary widely with the root cause and Subaru model; each issue on this page carries its own estimate where one is published.
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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.