New technical bulletin # 26-NA-033 identifies a possible software anomaly affecting the 2025 Chevrolet Tahoe, Suburban, GMC Yukon and Yukon XL equipped with the LZ0 diesel engine.

General Motors has released a new technical service bulletin addressing several diagnostic trouble codes (DTCs) that may appear on certain 2025 full-size SUVs equipped with the 3.0L Duramax diesel engine.

Bulletin # 26-NA-033, released September 30, 2026, identifies a potential Engine Control Module (ECM) software anomaly that may cause the Malfunction Indicator Lamp (MIL), commonly referred to as the Check Engine Light, to illuminate.

The bulletin is particularly noteworthy because several of the listed trouble codes are associated with fuel pressure regulation and other engine management systems. GM is advising technicians to investigate available ECM calibration updates before proceeding with conventional diagnostic procedures.

Which Vehicles Are Affected?

The bulletin applies to the following North American vehicles equipped with the 3.0L LZ0 Duramax diesel engine:

The bulletin does not currently identify the Silverado 1500 or Sierra 1500 as affected applications, despite those trucks sharing the LZ0 engine platform. These trucks received an update prior to this which excluded the SUV's

Nine Diagnostic Trouble Codes Identified

GM identifies nine diagnostic trouble codes that technicians may encounter, either as current faults or stored in vehicle history.

These include:

The inclusion of the P228-series codes is particularly interesting because these faults can lead technicians toward fuel pressure regulation concerns, including potential issues involving the high-pressure fuel system.

However, GM's latest bulletin establishes that a software anomaly may be responsible for the listed conditions.

This does not mean that every occurrence of these codes is software-related, nor does it eliminate the possibility of an actual mechanical or electrical failure.

GM's Recommended Correction

Rather than directing technicians to immediately replace components, GM has established a specific sequence for evaluating affected vehicles.

According to bulletin # 26-NA-033, technicians should first check whether any applicable campaigns require an ECM update.

If no campaign applies, technicians are instructed to check whether an updated ECM calibration is available for the vehicle.

If neither option provides an applicable update, technicians should continue with the appropriate diagnostic procedures outlined in GM Service Information.

The bulletin does not identify a specific replacement calibration number or direct technicians to replace any engine components.

It also does not state that every vehicle covered by the bulletin requires an ECM update.

Why Owners Should Be Aware of This Bulletin

Modern diesel engines rely heavily on ECM calibration to manage fuel delivery, emissions systems, turbocharger operation and numerous other functions.

A diagnostic trouble code identifies a condition detected by the vehicle's control system, but it does not necessarily establish which component is responsible.

For example, a fuel pressure regulation code may indicate an actual problem with fuel delivery or pressure control. However, the same general diagnostic category may also be affected by how the ECM monitors, interprets or responds to operating conditions.

With this bulletin, GM has formally acknowledged that a software anomaly may contribute to the listed faults on certain 2025 LZ0-equipped SUVs.

For owners experiencing an illuminated Check Engine Light accompanied by one or more of these codes, having the dealership check for applicable ECM campaigns and calibration updates is an appropriate starting point.

Owners should not assume that an ECM update will automatically resolve every occurrence of these DTCs. Vehicles with persistent faults, drivability concerns or actual fuel system problems may still require additional diagnosis.

Is This a Recall?

No recall is identified in bulletin # 26-NA-033.

This is a technical service bulletin providing dealership technicians with information and diagnostic direction for a potential software-related condition.

A technical service bulletin does not automatically establish that every vehicle within the listed model-year range has the condition or that a repair will be performed at no charge.

Owners should contact their servicing GM dealership to determine whether any applicable campaigns or calibration updates are available for their specific VIN.

Bulletin Information

• Bulletin Number: 26-NA-033

• Subject: Information on the LZ0 SUV Calibration Releases

• Release Date: September 30, 2026

• Version: 1

• Engine: 3.0L Duramax Diesel (LZ0)

• Model Year: 2025

• Region: North America

Source: General Motors Technical Service Bulletin # 26-NA-033, released September 30, 2026.