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2017 Legacy CVT Shudder and P0700 Code

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Mike T. · rep 0 · May 25, 2:13 AM · 1 replies · solved · Question

Vehicle: 2017 Subaru Legacy 2.5i Premium

My 2017 Subaru Legacy 2.5i Premium has recently started developing a noticeable shudder or vibration, especially when accelerating from a stop or at lower speeds. It's becoming quite concerning. To top it off, the Check Engine Light (CEL) came on, and when I scanned it, I got a P0700 code.

I know P0700 means the Transmission Control Module (TCM) has requested the MIL (CEL) to turn on. This makes me think it's directly related to the transmission shudder. Is my CVT failing? What are the common issues with these CVTs that cause shuddering and this code?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:13 AM

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The P0700 code on your 2017 Subaru Legacy, combined with a shudder during acceleration, strongly indicates an internal issue within the Continuously Variable Transmission (CVT). The P0700 is a generic code that tells you the Transmission Control Module (TCM) has detected a fault and has illuminated the Check Engine Light, but it doesn't specify the exact problem. A more advanced scan tool is usually needed to pull the specific Subaru-proprietary transmission codes stored in the TCM.

Common Causes of CVT Shudder and P0700:

  • CVT Fluid Degradation/Low Level: Old or insufficient CVT fluid can lead to poor lubrication and increased friction, causing shudder. Subaru CVTs require specific fluid (Subaru High Torque CVT Fluid or Subaru CVTF-II).
  • Torque Converter Issues: The torque converter can sometimes be a source of shudder, especially if the lock-up clutch is failing or glazing.
  • Valve Body Malfunction: The valve body controls hydraulic pressure and fluid flow within the CVT. Issues here can lead to incorrect pressure, causing shudder or slipping.
  • Worn Belt/Pulleys: Internal wear on the CVT's steel belt or pulley surfaces can lead to slippage and shudder. This is a more severe internal failure.
  • Software Glitch/TCM Fault: Less common, but sometimes a software update or a faulty TCM itself can cause issues.

Diagnostic Steps (for a professional):

  1. Retrieve Specific TCM Codes: A Subaru-specific scan tool will be used to pull the detailed 'P' codes from the Transmission Control Module. These codes will pinpoint the exact area of concern (e.g., specific solenoid faults, pressure sensor issues, etc.).
  2. Inspect CVT Fluid: Check the fluid level and condition. Dark, burnt-smelling fluid is a bad sign.
  3. Perform Driveability Tests: The technician will drive the vehicle to replicate the shudder and observe transmission behavior in various conditions.
  4. Monitor Live Data: Real-time data from the TCM, including line pressure, solenoid operation, and temperature, will be analyzed to identify anomalies.
  5. Check for Technical Service Bulletins (TSBs): Subaru may have issued TSBs for known CVT issues on your model year.

When to See a Shop:

Given the P0700 code and the shudder, it is critical to have your Legacy inspected by a Subaru dealership or a reputable transmission specialist as soon as possible. Driving with a shuddering CVT can lead to further, more severe damage, potentially requiring a complete transmission replacement. Do not attempt a simple CVT fluid drain and fill without proper diagnosis, as it may not resolve the underlying issue and could mask symptoms. A professional diagnosis is essential to determine if it's a fluid issue, a component failure, or a more extensive internal problem.

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