P0740 Code: Subaru Impreza (2017-2023) - Causes, Symptoms & Fixes

Below is a comprehensive diagnostic guide for OBD-II code P0740 as it may appear on a 2017-2023 Subaru Impreza. The data you provided from NHTSA shows no owner complaints and no recalls for this exact combination, so there are no statistically reported failure counts or recall notices to cite. No recalls found in NHTSA database. P0740 is a real diagnostic code associated with the torque converter clutch (TCC) in many automatic transmissions, including Subaru’s CVT (Lineartronic) systems, but actual failure frequencies for this specific model/year are not reflected in the current dataset.

CODE MEANING AND SEVERITY

• Code meaning: P0740 = Torque Converter Clutch Circuit Malfunction (TCC Circuit Malfunction). In practice, this indicates an issue with the torque converter’s lockup circuit or its control signals—either the circuit itself, the transmission control module (TCM) commands, or the physical TCC (lockup clutch) within the transmission.
• Severity and impact:
  • Symptoms can include poor acceleration, shudder or slipping, reduced fuel economy, and in some cases a limp or degraded drive feel.
  • If left untreated, prolonged TCC problems can raise transmission temperature and wear, potentially leading to further transmission damage.
  • On a Subaru Impreza with a CVT, loss of lockup can cause higher engine RPM at cruise and poorer highway efficiency.
  • The check engine light (CEL) or transmission warning may illuminate, and a D or L range may be selected by the powertrain/TCM as a protective measure.

COMMON CAUSES ON SUBARU IMPREZA

Note: These are typical contributors to P0740 in a Subaru CVT context; the exact root cause must be confirmed via testing.

• Faulty TCC solenoid or valve body issue: The solenoid that controls the lockup clutch may be sticking, failing, or misbehaving due to wear or contamination.
• Electrical / wiring problems: Damaged, corroded, or loose connectors and wiring to the TCC solenoid or the transmission controller (TCM/ECM) can cause intermittent or persistent malfunctions.
• Transmission fluid (CVTF) issues: Low fluid level, degraded/aged CVTF, or using an incorrect fluid type can affect TCC operation and hydraulic pressure.
• Overheating or poor cooling: CVT systems rely on adequate cooling; overheating can affect TCC performance and overall valve body operation.
• Internal valve body or pressure issues: Foreign material, wear, or sludge in the valve body can impair TCC hydraulic control.
• Torque converter wear or mechanical fault: Internal wear or damage to the lockup clutch or associated components can create a malfunction code.
• Software or calibration needs: Occasionally, TCM/ECM software requires updates or recalibration to properly command lockup across driving conditions.
• External driveline issues masking TCC symptoms: In some cases, problems with the driveshaft, wheel bearings, or other drivetrain components can mimic or compound TCC symptoms.

SYMPTOMS (typical for P0740 on CVT Impreza)

• Check Engine Light or Transmission Warning Light illuminated.
• Inconsistent or harsh shifting, especially under steady highway/cruise conditions.
• Decreased highway fuel economy; higher engine RPM at a steady speed due to loss of lockup.
• Transmission may shift into a failsafe mode or “limp” condition, reducing performance.
• Occasional shudder, especially when the TCC attempts to lock or unlock.
• No obvious noise in many cases, but some owners report whines or clunks corresponding to lockup events.
• Cruise control or throttle response may feel uncertain as the TCC control logic adapts.

DIAGNOSTIC STEPS

Caution: CVT systems require proper tool qualifications and fluids. When in doubt, consult a qualified technician.

• Step 1: Confirm and document

  • Read the P0740 code and any related codes (if present). Note freeze-frame data, engine load, vehicle speed, coolant temperature, and transmission fluid temperature at the time of the fault.
  • Confirm if there are any signs of transmission overheating or coolant/CVTF issues.

• Step 2: Inspect fluid and fluid-related conditions

  • Check CVTF level and condition. For CVTs, use the Subaru-recommended CVTF type and follow the correct procedure for checking and adding fluid at the specified temperature.
  • Look for burnt smell, metallic contamination, or dark, sludgy fluid. Any of these may indicate internal wear, contamination, or overheating.
  • Confirm the correct service interval has been followed and whether recent fluid replacement used the proper CVTF.

• Step 3: Inspect electrical and connections

  • Inspect TCC solenoid wiring and the valve body connectors for signs of corrosion, bent pins, or damaged insulation.
  • Check the grounds and the TCM/ECM connection to ensure proper electrical communication.
  • Look for any BCM or transmission control software update notices that may relate to tuning of the TCC.

• Step 4: Interpret live data (scanning)

  • With a capable scan tool, monitor the TCC solenoid circuit and TCC PWM (pulse width modulation) signals. Verify whether the lockup is commanded and whether it actually engages at the expected vehicle speeds (often around 35-60 mph, depending on gear and load).
  • Check for abnormal duty cycles, mis-timed lockup, or no lockup engagement at cruising speeds.
  • Look for other related data: transmission temperature, line pressure (if the data is available on the tool), and any intermittent loss of communication with the TCM.

• Step 5: Fluid and component tests

  • If the fluid is suspect, perform a controlled CVTF service using the manufacturer-recommended procedure and fluid.
  • If no fluid issues are found, test the TCC solenoid and pressure regulation in the valve body. This typically requires the transmission to be partially disassembled and tested in a controlled setting.
  • Consider testing or inspecting the torque converter for internal faults, which may require transaxle removal and inspection.

• Step 6: Additional testing and ownership considerations

  • If a software/TCM issue is suspected, check for available TCM/ECM software updates and service bulletin information from Subaru and the dealer network.
  • If diagnostic steps point toward internal transmission issues (wear, valve body damage, or torque converter failure), a professional diagnosis is recommended.

• Step 7: Decision point

  • If the TCC circuit is confirmed faulty and the vehicle’s operation is significantly impacted (slipping, overheating, reduced drive), plan repairs accordingly.
  • If the TCC is intermittently functioning but not causing major drive issues, a staged approach (fluid service, solenoid/valve body repair, software update) may be appropriate.
  • If there is extensive internal transmission damage or the torque converter itself is compromised, an engine/transmission replacement or rebuild may be necessary.

RELATED CODES

• P0740 is the primary code for Torque Converter Clutch Circuit Malfunction.
• Related torque-converter/transmission codes commonly observed in similar failure families (definitions can vary by manufacturer and software):
  • P0741: TCC Circuit Performance or Stuck Off
  • P0742: TCC Circuit Stuck On (or low) depending on the system
  • P0743/P0744: Additional TCC circuit fault variants (flow and signal anomalies)
• Note: Exact definitions can vary by OBD-II standard and Subaru’s/vehicle’s diagnostic software. Use the code family to guide diagnosis, but rely on live data and service information for final interpretation.

REPAIR OPTIONS AND COSTS (2025 PRICES)

Important: Prices vary by region, dealer vs independent shop, and the specific CVT version in your Impreza. The figures below are approximate ranges to help plan your budget.

• Basic diagnostic fee

  • Range: $80–$150 (some shops waive this with a subsequent repair)

• Transmission fluid service (CVTF change)

  • Parts: CVTF bottle(s) and any gaskets/seals if needed
  • Labor: 1–3 hours
  • Typical total: $180–$350

• TCC solenoid/valve body service

  • Parts: TCC solenoid or valve body components (if serviceable)
  • Labor: 2–5 hours
  • Typical total: $400–$1,200

• Valve body repair or replacement

  • Parts: Valve body assembly or repair kit
  • Labor: 3–6 hours
  • Typical total: $600–$1,500

• Torque converter replacement

  • Parts: Torque converter
  • Labor: 4–8 hours
  • Typical total: $1,200–$2,500 (plus fluids and possible seals)

• Transmission rebuild or CVT replacement

  • Parts: Rebuilt or replacement CVT unit or major overhaul components
  • Labor: 8–20 hours (highly variable)
  • Typical total: $3,500–$7,500 (rebuilt) or $4,000–$8,500+ (new or exchanged CVT)

• Additional considerations

  • If a software/TCM update is required, dealer-level programming costs may apply ($100–$300, sometimes included with a service).
  • If driveline components (driveshafts, wheel hubs, or bearings) are suspected in contributing to symptoms, require separate diagnosis and costs.

DIY VS PROFESSIONAL

• DIY-friendly tasks (if you have the right tools and fluids):
  • Checking CVTF level and fluid condition (with the correct Subaru CVTF and at the proper temperature)
  • Inspecting exterior electrical connectors and grounds for visible corrosion or damage
  • Basic diagnostic reading of the code with an OBD-II scanner and observing live data for TCC signals
• DIY limitations and cautions:
  • CVT fluids and valve body work often require specialized service procedures and tools.
  • Replacing the TCC solenoid, valve body, or torque converter typically requires transmission removal and/or disassembly; this is best performed by a trained technician with CVT experience.
  • Incorrect CVTF type or over/under-filled fluid can cause severe CVT damage; only use manufacturer-approved fluid and follow the official procedure.
• Professional route:
  • If the DTC appears with driveability issues (slipping, overheating, no lockup), or if you lack the equipment to properly test TCC and CVT internals, seek a certified automotive technician or a transmission specialist with Subaru CVT experience.

PREVENTION

• Regular maintenance and fluid care
  • Use only Subaru-approved CVTF; follow the maintenance interval recommended in your owner’s manual.
  • Change CVTF at the recommended intervals or when inspection indicates degradation; do not ignore coolant or overheating symptoms.
• Cooling system health
  • Ensure the CVT cooling system (cooler, hoses, radiator) is clean and functioning; overheating accelerates CVT wear and TCC issues.
• Driving habits
  • Gentle acceleration and avoiding sustained high-load towing or aggressive throttle can reduce TCC wear and overheating.
  • When cruising, maintain steady speeds to encourage proper lockup operation.
• Electrical health
  • Keep electrical connections clean and tight; address any corrosion or damaged wiring promptly.
• Software updates
  • Check for and install any Subaru TCM/ECM software updates related to transmission control as recommended by the dealer.

Important data note

• The data you provided shows no NHTSA owner complaints and no recalls for this exact make/model/year/issue combination. This means there are no published complaint-based reliability statistics or recall-based guidance for P0740 on 2017–2023 Subaru Impreza in the provided dataset. The diagnostic guidance above relies on general automotive knowledge and typical CVT/TCC behavior, not on specific complaint data for this exact vehicle in the supplied data.

If you’re dealing with a P0740 on a 2017–2023 Subaru Impreza, use this guide as a structured starting point, but prioritize a hands-on diagnostic using a capable scan tool and, if needed, professional CVT service.