GM Slow DC Charging Bulletin for Silverado EV & Sierra EV

GM has issued a service bulletin that helps explain why some of its large Ultium-based electric vehicles may DC fast charge slower than expected.

The bulletin, listed as PIP6123 and titled “Slow DC charging,” applies to several GM electric vehicles, including the Chevrolet Silverado EV, GMC Sierra EV, GMC Hummer EV, Cadillac Escalade IQ, and Cadillac Escalade IQL.

This is not a recall. It is a service bulletin intended to help GM technicians diagnose customer complaints where DC fast charging speeds are lower than expected.

What vehicles are listed in the bulletin?

According to the GM bulletin, the affected vehicle lines include:

  • 2024-2026 Chevrolet Silverado EV
  • 2024-2026 GMC Sierra EV
  • 2022-2026 GMC Hummer EV
  • 2025-2026 Cadillac Escalade IQ
  • 2026 Cadillac Escalade IQL

The bulletin applies to vehicles in North America and references vehicles without RPO EWX, which GM describes in the bulletin as the 14 MOD Pack.  The Silverado EV & Sierra EV have three current battery pack options.  Standard (14 Module Pack), Extended Range (20 Module pack), and Max (24 Module pack).  So this would appear to exclude standard pack vehicles.

What is the slow charging issue?

GM says a customer may notice slower-than-expected DC fast charging. The example given in the bulletin is a vehicle charging at 140 kW or less on a 350 kW or higher DC fast charging station.

The bulletin also states that the vehicle may be limited to 400-volt charging.

That detail matters because GM’s large Ultium trucks and SUVs are designed to take advantage of higher-voltage charging behavior under the right conditions. If the vehicle stays in a lower-voltage charging configuration, the owner may see charging speeds that feel disappointing compared with what the vehicle is normally capable of delivering.

What does GM say may cause it?

GM identifies two possible causes in the bulletin:

  • A potential capacity mismatch within the high-voltage battery
  • A low 12-volt battery state of charge below 40 percent

According to the bulletin, either condition can cause the high-voltage battery to remain in a parallel charging configuration instead of moving into an 800-volt series charging configuration.

In plain English, the vehicle may not be switching into the charging configuration needed for its best DC fast charging performance.

Why the 12-volt battery matters

One of the more interesting parts of the bulletin is that GM points to the 12-volt battery state of charge as a possible factor.

Owners often think of DC fast charging as only involving the large high-voltage battery pack. But modern EVs still rely heavily on the 12-volt system to power modules, computers, relays, and control systems. If that 12-volt battery is low enough, it can affect how the vehicle manages charging.

In this bulletin, GM specifically tells technicians to check the low-voltage battery state of charge and address it through service diagnostics if it is at or below 40 percent.

What does the dealer check?

The bulletin lays out two main diagnostic paths for GM technicians.

First, technicians are directed to check high-voltage battery capacity values through the Battery Energy Control Module. GM tells technicians to compare two battery pack capacity values. If the smaller value divided by the larger value is 0.90 or less, the bulletin directs the technician to perform a battery pack capacity fast learn procedure.

Second, technicians are directed to check the 12-volt battery state of charge. If the 12-volt battery is at or below 40 percent, the technician is instructed to follow GM service information for battery inspection and testing.

What owners should not do

The bulletin includes a clear warning for technicians: before reviewing the preliminary information, do not perform manual code clearing, additional programming events, or 12-volt power disconnections.

For owners, the takeaway is simple: this is not something to try to reset or diagnose yourself. If your vehicle is repeatedly fast charging slower than expected, document what happened and let the dealer inspect it properly.

What information should you bring to the dealer?

If you own one of these GM EVs and are seeing unusually slow DC fast charging, it may help to bring your dealer specific information, including:

  • The charging station provider and location
  • The charger’s advertised power level, such as 350 kW
  • Your starting battery percentage
  • Your approximate charging speed in kW
  • Whether the issue happened more than once
  • Photos of the charger screen or vehicle charging screen, if available
  • A note asking whether GM bulletin PIP6123 applies to your concern

That kind of detail can help separate a vehicle-side issue from a charging-station limitation, cold battery behavior, a high state of charge, or other normal DC fast charging slowdowns.

Why this matters for Silverado EV and Sierra EV owners

The Silverado EV and Sierra EV are marketed around large batteries, long driving range, and serious road-trip capability. DC fast charging performance is a major part of that ownership experience.

If a truck capable of much higher charging speeds is only seeing around 140 kW or less on a high-powered charger, that can significantly change the road-trip experience. It can also create confusion for owners who expect faster charging from GM’s large Ultium battery platform.

Bottom line

GM bulletin PIP6123 gives dealers a specific path to investigate slow DC fast charging complaints on several large GM EVs.

The key owner takeaway is that slow charging may not always be the charger’s fault. In some cases, GM says the vehicle may remain limited to a 400-volt charging configuration due to a high-voltage battery capacity mismatch or a low 12-volt battery state of charge.

If you own a Silverado EV, Sierra EV, Hummer EV, Escalade IQ, or Escalade IQL and repeatedly see unusually low charging speeds on powerful DC fast chargers, this is a bulletin worth mentioning to your dealer.

Got questions? Drop a comment I love hearing from all of you.

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Source: GM PIP6123

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Ken, EV Outdoors

Ken, EV Outdoors

I'm an EV analyst focused on a real-world, objective take on electric vehicle ownership. I've been driving EVs for over a decade and have owned 8 across multiple brands, with seat time in many more. EV Outdoors is independent analysis of EV towing, road-tripping, and the realities manufacturers leave out of the brochure.

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