P2721 on 2020-2023 Subaru Legacy: Pressure Control Solenoid 'D' Circuit High Fixes

What's Unique About the 2020-2023 Subaru LEGACY

This issue is particularly notable on the 2020-2023 Subaru Legacy with the 2.5L engine because Subaru has officially acknowledged a specific weakness. A Technical Service Bulletin (TSB 16-149-25) was issued explaining that condensation can accumulate inside the transmission cover and seep into the main electrical connector, causing a short circuit and triggering this code. The official fix involves replacing the entire control valve assembly (which contains the solenoids) with an updated part and adding a new protective connector cover to prevent future moisture intrusion. This makes it less of a random failure and more of a known pattern for this specific vehicle and its TR580 transmission.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle. 👇

Symptoms You May Notice

• Check Engine Light and/or AT OIL TEMP light illuminated
• Harsh, jerky, or delayed shifting
• Vehicle entering 'limp mode' with limited power and gear ratios
• A feeling of the transmission slipping, where engine RPMs increase without a corresponding increase in speed
• Hesitation or shuddering when accelerating from a stop
• Inability to shift or move after coming to a stop.
🎬 See: 5 critical warning signs your Subaru CVT is failing.

Most Likely Causes

1. Defective Transmission Control Valve Body Assembly 🔴 High Probability → Shop Transmission Valve Body Subaru TSB 16-149-25 directly identifies a design issue where moisture can enter the harness connector for the control valve, causing a short circuit and this specific code. The fix involves an updated valve body and a new connector cover. This is the most common point of failure for this code on this platform.
   How to confirm: A technician will confirm by checking for the presence of P2721 and related codes (P2763, P0974, P0977), inspecting the transmission connector for moisture or corrosion, and following the diagnostic procedure outlined in TSB 16-149-25.
   Typical fix: Replace the entire CVT control valve body assembly with the updated part and install the new connector cover as per TSB 16-149-25. The repair is often covered under Subaru's CVT warranty extension.
   Est. part cost: $800-$1300
2. Damaged Wiring Harness or Connector 🟡 Medium Probability The TSB mentions that moisture intrusion into the connector is a primary cause, which points to a vulnerability in the external wiring and connections. A short to voltage in the harness can also trigger a 'Circuit High' code. While less common than the valve body itself failing, the connector is a key part of the TSB's focus.
   How to confirm: Visually inspect the transmission harness and connectors for any signs of corrosion, water damage, or physical damage. A multimeter would be used to test the circuit for a short to power between the TCM and the valve body connector.
   Typical fix: Repair the damaged section of the wiring harness or replace the affected connector. Per the TSB, a new protective connector cover (Part No. 31712AA001) is required during the valve body replacement to prevent recurrence.
   Est. part cost: $50-$300
3. Faulty Transmission Control Module (TCM) ⚪ Low Probability → Shop Transmission Assembly
   How to confirm: This is a diagnosis of exclusion. If the valve body and wiring have been tested according to TSB 16-149-25 and are confirmed to be good, the TCM itself may be the issue. This is the least likely cause.
   Typical fix: Replace and reprogram the Transmission Control Module.
   Est. part cost: $600-$1000

Diagnosis Steps

1. Scan the TCM for diagnostic trouble codes. Note P2721 and any other related codes (P2763, P0974, P0977, P0700).
2. Perform a Vehicle Coverage Inquiry on Subarunet to check for applicability of the CVT warranty extension (10yr/100k miles).
3. Check for any applicable Technical Service Bulletins. For this vehicle, TSB 16-149-25 is directly relevant.
4. Inspect the main transmission electrical connector for signs of moisture, corrosion, or damage, as indicated by the TSB.
5. If no external damage is found, follow the TSB's diagnostic flowchart, which involves testing the resistance and voltage of the solenoid circuits from the TCM connector to check for a short to power.
6. If the wiring tests good, the TSB directs the replacement of the control valve body and the installation of a new connector cover.
7. After replacement, clear the DTCs, perform any required TCM relearn procedures, 🎬 Watch: How to properly refill fluid and perform the relearn. and conduct a test drive to verify the repair is successful.

Parts You'll Likely Need

• CVT Control Valve Body Assembly (OEM #31825AA055) — This is the primary part identified by Subaru in TSB 16-149-25 to fix the P2721 code. It contains the problematic solenoid and has been updated for better durability. Part number may be superseded; always verify with VIN.
  Trusted brands: Subaru (OEM)
  OEM price range: $800-$1300
  Aftermarket price range: $300-$600 (Remanufactured)
• Transmission Connector Cover (OEM #31712AA001) — This new part is required by TSB 16-149-25 to prevent the moisture intrusion that causes the electrical short in the first place.
  Trusted brands: Subaru (OEM)
  OEM price range: $20-$40
• Subaru High Torque CVT Fluid CVTF-II (OEM #SOA427V1660) — The transmission fluid must be drained to replace the valve body and will need to be replaced with new, correct-spec fluid. Approximately 5-6 quarts are needed for a valve body service.
  Trusted brands: Subaru (OEM)
  OEM price range: $20-$30 per quart

Related Codes That Often Appear With This One

• P2763 — Torque Converter Clutch Pressure Control Solenoid Control Circuit High. This code is listed in the same TSB (16-149-25) and is caused by the same valve body moisture issue.
• P0974 — Shift Solenoid 'A' Control Circuit High. This is also listed in TSB 16-149-25 as being related to the same root cause.
• P0977 — Shift Solenoid 'B' Control Circuit High. This is another code mentioned in TSB 16-149-25 with the same fix.
• P0700 — Transmission Control System Malfunction. This is a generic code indicating the TCM has stored a fault, and it will almost always be present alongside a more specific code like P2721.

Technical Service Bulletins (TSBs) & Recalls

• 16-149-25: Announcing a new TR580 control valve and connector cover to address DTCs P2721, P2763, P0974, and P0977 caused by moisture intrusion into the harness connector.
• 16-155-25R: Details the CVT Warranty Extension to 10 years/100,000 miles for various models, including the 2019+ Legacy, providing crucial coverage information for this repair.

Platform-Specific Known Issues

• The 2020-2023 Legacy models equipped with the TR580 CVT are subject to TSB 16-149-25, which details a known issue of moisture ingress at the transmission connector leading to 'Circuit High' codes, including P2721.
• Subaru has extended the warranty on many of its CVT transmissions to 10 years/100,000 miles, whichever comes first. Owners should check with a Subaru dealer by providing their VIN to see if their vehicle is covered under this extension, as this specific valve body repair is frequently covered.

Mechanic-Grade Diagnostic Values

• Resistance of Lock-up Duty Solenoid at transmission connector T4 — expected: 10 - 13.5 Ohms. Failure: A reading outside this range, especially 0 ohms (short) or infinite (open), indicates a failed solenoid.
• Resistance of AWD Solenoid at transmission connector T4 — expected: 2 - 4.5 Ohms. Failure: A reading outside this range suggests a faulty AWD solenoid, which can be tested from the same connector.
• Resistance between transmission harness connector and transmission ground — expected: Less than 1 Ohm. Failure: Resistance greater than 1 Ohm indicates a poor ground connection, which can cause various electrical faults.

Scan Tool Commands That Help

• Subaru Select Monitor (or equivalent like Autel MaxiSys): Clear Memory / Clear AT Learning Values — This must be performed after replacing the valve body to erase the old, learned adaptive values from the TCM.
• Subaru Select Monitor (or equivalent like Autel MaxiSys): AT Learning / Compulsory Learning Mode — This is a mandatory procedure after clearing memory to allow the TCM to learn the operational characteristics of the new valve body. Failure to perform this can result in poor shifting and drivability issues.

Wiring & Ground Locations

• Transmission Ground Strap — A 12mm bolt securing a ground strap to the transmission case, which must be removed to take off a harness bracket during valve body replacement.. A poor or corroded ground connection can cause erratic behavior and high resistance in electrical circuits, potentially contributing to or mimicking circuit-high fault codes.
• Engine Harness Chafe Points — General areas to inspect for harness damage include near the ECM/TCM bracket, the front corner of the left cylinder head, and where the harness passes the upper control arm or shock tower.. While the TSB points to the connector, a 'Circuit High' code can also be caused by a wire in the harness chafing and shorting to a power source. If the connector shows no moisture, the harness routing should be inspected for damage.

Real Owner Repair Stories

• YouTube Commenter on MrSubaru1387 video (Subaru with TR580 Transmission (specific model not mentioned, but procedure is identical)) — Not specified, but required valve body replacement.
  ✅ What actually fixed it The owner was quoted $2,900-$3,000 by a dealership. They performed the valve body replacement themselves in approximately 3 hours using a remanufactured part that cost about $300, successfully fixing the issue.

OEM Part Supersession History

• 31825AA050, 31825AA051, 31825AA052, 31825AA053, 31825AA054 → 31825AA055 — Design changes to improve durability and prevent issues leading to various DTCs. The TSB for P2721 involves an updated valve body and a new connector cover to prevent moisture intrusion.
  Heads up: Always use the latest available part number (31825AA055) when replacing, as it contains all previous updates.
• N/A (Remanufactured Valve Bodies) → N/A
  Heads up: When sourcing remanufactured TR580 valve bodies, you must identify if your original unit has 'No Worm Track', '1 Worm Track', or '2 Worm Tracks' on the casting. These variations are not interchangeable, and ordering the wrong one will prevent proper installation.

Model Year Variations Within This Range

• 2020-2023: No significant variations in the cause or fix for code P2721 have been documented within this specific model year range for the Legacy. The primary known failure mode and the TSB-directed repair apply consistently across these years.