New GM Bulletin Targets Harsh 10L80 Engagement After Auto Stop on 2026 3.0 Duramax Trucks

GM has released a new technical service bulletin, # 25-NA-325, addressing a harsh or jerky engagement concern when the engine restarts after an Auto Stop event on certain 2026 Chevrolet Silverado 1500 and 2026 GMC Sierra 1500 trucks equipped with the LZ0 3.0L Duramax and MQB 10L80 10-speed automatic transmission.

If your 2026 3.0 Duramax feels like it “slams” into gear when Auto Stop lets go, this bulletin is for you.

Vehicles Covered by # 25-NA-325

According to the bulletin, the affected vehicles are:

• 2026 Chevrolet Silverado 1500

  • Engine: LZ0 3.0L Duramax

  • Transmission: MQB 10L80

• 2026 GMC Sierra 1500

  • Engine: LZ0 3.0L Duramax

  • Transmission: MQB 10L80

Regions called out in the bulletin include North America, Argentina, Brazil, Bolivia, Chile, Colombia, Ecuador, Peru, Uruguay, Europe, Middle East, and the Philippines.

In other words, this is not just a North American issue—this calibration applies globally wherever these trucks are sold.

The Complaint: Harsh Engagement Exiting Auto Stop

The customer concern is pretty specific:

When the engine restarts exiting an Auto Stop event, the transmission may jerk or have a harsh engagement.

In real-world terms, that might feel like:

• A sharp bump when the light turns green and you start to go.

• A noticeable “clunk” when the engine fires back up and you release the brake.

• The truck feeling like it’s being “hit from behind” slightly as Auto Stop lets go.

If the harshness is only present when Auto Stop is involved (and not during normal forward or reverse shifts), this calibration bulletin is likely related.

The Cause: TCM Calibration Not Up to Date

GM’s stated cause is straightforward:

The cause of the condition may be the Transmission Control Module (TCM) calibration not being up to date.

Modern transmissions like the 10L80 rely heavily on software to coordinate the torque converter, clutches, engine torque management, and Auto Stop/Start behavior. A small timing mismatch between the engine restart and clutch apply can show up as a harsh engagement.

In short:This is a software refinement issue, not a “your transmission is failing” issue.

The Fix: Update the Transmission Control Module (TCM)

The correction GM outlines is simple:

Check for the latest transmission calibration/software in the TCM and update as needed.

Key points:

• The dealer connects the truck to GM’s service tools and checks if a newer TCM calibration is available.

• If a newer calibration exists, they reprogram (flash) the TCM with the updated software.

• If the latest calibration is already installed, they are not supposed to reflash it again. The bulletin specifically warns not to reflash the same software twice.

This is not a physical repair—no parts are replaced. It’s a software update aimed at smoothing out the transition from Auto Stop to moving off the line.

Who Can Perform This Repair?

GM is clear that this bulletin:

• Must be completed only by certified repair facilities that meet the specific training, tool, and equipment requirements for the brand and model.

• Must be performed by a technician who has successfully completed the required training.

This is not something an independent shop or DIY owner can do at home. It requires access to GM’s factory programming tools and current service information.

What Owners Should Do Next

If you own a 2026 Silverado or Sierra 1500 with the LZ0/10L80 and you notice harsh engagement when Auto Stop releases:

1. Document the condition.

   • Note when it happens (stop lights, stop-and-go traffic, hot/cold engine, etc.).

   • If it is clearly tied to Auto Stop restarting the engine, that’s useful information.

2. Schedule a visit with your GM dealer.

   • Explain that you are experiencing harsh engagement when exiting Auto Stop.

   • Ask them to check TSB # 25-NA-325 and confirm whether a newer TCM calibration is available for your truck.

3. Ask about coverage.

   • In many cases, calibration updates like this are performed under warranty if the vehicle is still within the applicable coverage and the condition is present.

   • The bulletin itself simply instructs dealers on what to do; it does not automatically guarantee free repairs outside normal warranty terms. Your individual situation may vary.

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Why This Matters for Long-Term Durability

While this bulletin is mainly about drivability and comfort, proper calibration is also good for:

• Transmission clutch life – smoother apply events mean less shock load on the hardware.

• Owner confidence – harsh or jerky behavior can make drivers worry that something is “wrong” with a brand-new truck.

• Refinement – the 10L80 is capable of very smooth shifts when the software is dialed in.

  
  

If you just took delivery of a 2026 3.0 Duramax and something feels off when Auto Stop kicks back out, it’s worth having your dealer check for this update rather than assuming you have a mechanical failure.