P1955 on 2020-2024 Chevrolet Corvette: Transmission Fault Guide

What's Unique About the 2020-2024 Chevrolet CORVETTE

The C8 Corvette (2020-2024) was the first vehicle to feature the TREMEC TR-9080, a complex 8-speed Dual-Clutch Transmission (DCT) designed exclusively for it. Code P1955 is specific to the internal diagnostics of this advanced transaxle. While early bulletins suggested procedures like fluid flushes or solenoid cleaning, the latest official GM guidance (TSB #23-NA-139) for standard models is direct: the code indicates a non-serviceable internal failure requiring transmission replacement. A different service procedure exists for the E-Ray hybrid model, which uses an auxiliary fluid pump; for that model, P1955 is caused by a clogged transmission pan filter and is fixed by replacing the filter, not the entire transmission.

Diagnostic Flowchart

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

Symptoms You May Notice

• "Service Transmission" message on the Driver Information Center (DIC).
• Check Engine Light (Malfunction Indicator Lamp) is illuminated.
• Vehicle may enter a reduced power or 'limp mode'.
• Erratic or failed shifting.
• "Emergency Creep Mode Disabled" mes 🎬 See this video for common causes of service transmission messages.sage.

Most Likely Causes

1. Non-Serviceable Internal Transmission Failure 🔴 High Probability → Shop Transmission Assembly As per GM TSB #23-NA-139, the root cause is an internal fault within the TR-9080 DCT that cannot be repaired at the dealer level. Speculation based on the evolution of GM's diagnostic advice suggests the failure stems from a systemic loss of hydraulic pressure, potentially caused by internal debris from manufacturing or component wear clogging critical passages or solenoids. GM's early interest in collecting used transmission filters from the initial 7,500-mile service for analysis supports this theory.
   How to confirm: Confirming the presence of DTC P1955 (current or in history) with a GDS2 diagnostic scan tool is the primary method. Per GM's directive, if this code is found, no further diagnosis is needed. One owner on CorvetteForum.com reported their dealer confirmed the code and GM immediately authorized a transmission replacement under warranty.
   Typical fix: Complete replacement of the transmission assembly. The repair is typically covered under the 5-year/60,000-mile powertrain warranty.
   Est. part cost: $7,500-$9,000 for a new transmission assembly from a dealer. A third-party seller listed a unit with part number 24042874 for approximately $4,500.

Rare But Worth Checking

• Clogged Transmission Pan Fluid Filter (E-Ray Models Only): → Shop Transmission Assembly On 2024+ Corvette E-Ray hybrid models, P1955 can be caused by auxiliary pump cavitation due to a clogged filter. The fix is a filter replacement, not a full transmission replacement. This procedure does NOT apply to standard Stingray or Z06 models. The pan bolts are single-use and must be replaced.

Diagnosis Steps

1. Connect a professional-grade OBD-II scanner (like the GM GDS2) to the vehicle.
2. Read codes from the Transmission Control Module (TCM).
3. If P1955 and/or P0867 are present (either current or in history), consult GM Service Bulletin #23-NA-139.
4. For standard Corvette models (non-E-Ray), the bulletin directs the replacement of the entire transmission assembly. No further diagnosis is recommended.
5. IMPORTANT: Per TSB #23-NA-139, do NOT drain the transmission fluid prior to replacement. GM Engineering requests the transmission be returned with the original fluid for analysis.
6. For Corvette E-Ray models, consult the relevant TSB, which directs the replacement of the transmission pan fluid filter.
7. Do not attempt to replace the Main Control Valve (MCV) or perform a fluid flush (on non-E-Ray models) as these will not resolve the issue.

Parts You'll Likely Need

• 8-Speed Dual Clutch Transmission Assembly (OEM #24042874) — According to GM TSB #23-NA-139, this is the only authorized repair for code P1955 on standard 2020-2024 Corvettes.
  Trusted brands: ACDelco (GM Genuine)
  OEM price range: $7500-$9000
  Aftermarket price range: N/A
• ACDelco FFL-4 DCT Fluid (OEM #19418016 / 10-4130) — The new transmission will require a full fill of this specific fluid. The system holds approximately 11.6 quarts (11 liters).
  Trusted brands: ACDelco
  OEM price range: $35-$50 per quart
  Aftermarket price range: N/A

Related Codes That Often Appear With This One

• P0867 — P0867 (Transmission Fluid Pressure Performance) is almost always set along with P1955. GM service bulletin #23-NA-139 groups these two codes together as indicating the same non-serviceable internal failure.
• P0700 — P0700 is a generic code indicating the Transmission Control Module (TCM) has requested the Check Engine Light to be turned on. It signals that a more specific transmission code, like P1955, is stored in the TCM.
• P2853, P2854, P2855, P2856 — A real-world owner case on CorvetteForum documented these codes, which relate to shift fork position sensor performance, appearing at the same time as P1955 and P0868 (likely P0867). This indicates the systemic pressure loss may be causing secondary faults with sensor readings and fork actuation.

Technical Service Bulletins (TSBs) & Recalls

• 23-NA-139: 'Information on Internal Transmission Faults...Service Transmission Message Displayed...DTC P1955 and/or P0867 Set'. This is the primary TSB, which states that for non-E-Ray models, the transmission must be replaced. It explicitly warns against replacing the MCV.
• GM TechLink Article (re: E-Ray): 'Service Transmission Message Displayed...DTC P1955 and/or P0867 Set'. This bulletin applies ONLY to 2024+ Corvette E-Ray models and directs technicians to replace the transmission pan fluid filter to correct auxiliary pump cavitation.
• 21-NA-033: An earlier bulletin mentioned in relation to fluid checks, but now superseded by 23-NA-139 for this specific fault.

Platform-Specific Known Issues

• GM has issued multiple revisions of service bulletin #23-NA-139, which supersedes PIP5797E. The latest version from November 2023 clarifies that for standard Corvettes, a P1955 code requires transmission replacement.
• A separate bulletin addresses the same codes on the Corvette E-Ray, where the cause is a clogged filter leading to auxiliary pump cavitation.
• Early in the C8's life (Nov 2021), GM issued a TSB asking dealers to collect and return all DCT filters from the initial 7,500-mile service for analysis, indicating an early investigation into fluid contamination and filtration issues.

Scan Tool Commands That Help

• GDS2: Transmission Service Fast Learn (SFL) — This procedure is mandatory after replacing the transmission assembly. It allows the new TCM to learn clutch apply pressures and shifting characteristics. Failure to perform this procedure can result in poor shift quality, component damage, or DTCs being set.
• GDS2: Hydraulic System Flush / Service Clean Procedure — This was part of an earlier, now-superseded diagnostic path for P1955 on non-E-Ray models, intended to clear debris from sticking solenoids. Per TSB 23-NA-139, this is no longer the recommended procedure for P1955, which now requires full replacement.

Wiring & Ground Locations

• Transmission Control Module (TCM) — Located on the passenger side of the vehicle, accessible by removing the rear wheel and wheel well liner.. While P1955 points to an internal transmission fault, a technician would still verify the TCM connector and harness are secure and free of damage as a preliminary step before condemning the transmission.
• G106 — Located on the passenger side of the engine block, above the starter.. This is a main ground point for the PCM/ECM to the engine. While the TCM is a separate module, ensuring all primary powertrain grounds are clean and tight is a fundamental step in diagnosing any major electronic fault code to rule out voltage drop or reference issues.

Real Owner Repair Stories

• CorvetteForum user 'Beerman1378' (2022 Chevrolet Corvette, built late 2021, 13,000 miles at failure.) — Check Engine Light, 'Emergency Creep Mode Disabled' message, and intermittent shifting problems that worsened as the vehicle warmed up.
  ❌ Tried (didn't work) No other repairs were attempted.
  ✅ What actually fixed it The dealer scanned the vehicle and found codes P1955, P0868, and several shift fork position codes (P2853, P2854, P2855, P2856). Based on the presence of P1955, GM immediately authorized a complete transmission replacement under the powertrain warranty.

OEM Part Supersession History

• Unknown → 24042874 — This is a common service part number for the complete TR-9080 transmission assembly for 2020-2023 models. Another part number, 24042873, has also been seen on used assemblies. GM often revises parts to improve reliability or address known failure modes.
  Heads up: The Z06 uses a different variant of the TR-9080 (M1M vs the Stingray's M1L) with a stronger clutch pack, and the E-Ray has an auxiliary pump, so part numbers are not interchangeable across all Corvette C8 models.

Model Year Variations Within This Range

• 2024+: The introduction of the Corvette E-Ray model brought a new cause for P1955. On the E-Ray, this code is caused by a clogged transmission pan fluid filter leading to auxiliary pump cavitation, and the fix is a filter replacement, not a full transmission replacement.
• 2022: The LT2 engine received fuel management system upgrades, including a new fuel pump and injectors, for the 2022 model year. While not directly related to the transmission, it marks a production change within the affected vehicle range.