What Do GM Transmission Codes MQB, MQC, MHT, MHS, and MI2 Actually Mean?

If you've scanned the QR code on your truck's door jamb, chances are you've come across transmission codes like MQB, MQC, MHT, or MHS.

A question I see fairly often is:

"What's the difference? Aren't they all 10-speed transmissions?"

The short answer is yes—but also no.

While these are all part of GM's 10-speed automatic family, the RPO (Regular Production Option) code identifies the specific version of the transmission that was installed in your truck from the factory. That version includes not only the transmission itself, but also its calibration, torque converter, shift strategy, controller, and how it interfaces with the vehicle.

Let's break it down.

First, What Is an RPO Code?

GM uses RPO (Regular Production Option) codes to identify every major component installed during production.

Beginning with newer GM trucks, these codes are stored inside the QR code located on the driver's door jamb. Scanning the QR code reveals your truck's complete build sheet, including the transmission RPO.

MQB

Primary application:

• 3.0L Duramax diesel

• Column shifter

Transmission:

• 10L80

This is the transmission most LM2 and many LZ0 owners will find.

Although it's mechanically a 10L80, GM assigned it its own RPO because it receives diesel-specific programming designed around the 3.0L's torque characteristics.

The calibration includes:

• Lower shift RPM

• Earlier torque converter lockup

• Different shift scheduling

• Torque management tuned for nearly 500 lb-ft available at very low engine speeds

  
  

MQC

Primary application:

• 3.0L Duramax diesel

• Electronic Transmission Range Selector (ETRS)

Transmission:

• 10L80

Mechanically, MQC is extremely similar to MQB.

The primary difference is that MQC was designed for trucks equipped with GM's electronic shifter instead of the traditional column shifter. GM documentation also groups MQC with ETRS-equipped vehicles in several service bulletins.

MHT

Primary application:

• 5.3L V8

• 6.2L V8

• Column shifter

Transmission:

• 10L80

MHT is the gasoline counterpart to MQB.

Instead of being optimized for diesel torque, its calibration is designed around higher engine RPM and the power characteristics of GM's V8 engines.

MHS

Primary application:

• 5.3L V8

• 6.2L V8

• Electronic shifter

Transmission:

• 10L80

Beginning with the refreshed trucks, GM introduced the MHS version of the transmission.

Compared to MHT, it includes:

• Electronic Transmission Range Selector (ETRS)

• Updated transmission controller

• New software architecture

• Support for over-the-air transmission calibration updates

Mechanically, it's still considered a 10L80, but electronically it's an evolution of the earlier version.

MI2

MI2 is the least commonly discussed because it is generally found in heavier-duty applications.

It is used in certain HD truck configurations and features:

• Heavy-duty calibration

• Different torque management

• HD vehicle integration

• Application-specific programming

Although it belongs to GM's 10-speed family, it isn't simply interchangeable with the half-ton versions.

Are These Different Transmissions?

This is where many owners get confused.

The answer is:

Mostly no.

The core transmission architecture remains the 10L80.

However, GM changes numerous components depending on the application, including:

• Torque converter

• Valve body calibration

• Solenoid programming

• TCM software

• Shift scheduling

• Converter clutch strategy

• Engine torque management

So while two trucks may both have a "10-speed," they may not drive the same—or even share identical service procedures.

Why Does the 3.0L Duramax Have Its Own Transmission Codes?

One thing that stands out is that GM created unique RPO codes specifically for the diesel.

Instead of using the same codes as the gasoline trucks, GM assigned:

• MQB

• MQC

This strongly suggests the diesel calibration differs enough that GM considers it a separate production configuration.

That makes sense when you consider the 3.0L Duramax produces nearly 500 lb-ft of torque just above idle. A transmission programmed for a gasoline V8 simply wouldn't deliver the same shift quality, converter lockup behavior, or towing performance. Community discussions also point to diesel-specific tuning as the primary distinction.

At a Glance

RPO	Engine	Shifter	Transmission	Primary Difference
MQB	3.0L Duramax	Column	10L80	Diesel calibration
MQC	3.0L Duramax	Electronic	10L80	Diesel calibration + ETRS
MHT	5.3L / 6.2L	Column	10L80	Gasoline calibration
MHS	5.3L / 6.2L	Electronic	10L80	Updated electronics and OTA capability
MI2	HD Applications	Varies	10-speed HD variant	Heavy-duty calibration

The important takeaway is that these RPO codes don't necessarily indicate an entirely different transmission. In most cases, they identify a specific version of the 10L80 that's been tailored for a particular engine, shifter configuration, and vehicle platform.

For 3.0L Duramax owners, MQB and MQC represent GM's diesel-specific implementation of the 10-speed automatic. The hardware is very similar to the gasoline versions, but the calibration, converter strategy, and control software are optimized for the diesel's unique power delivery.

Editor's Note: I'm digging deeper into the GM parts catalog to compare MQB, MQC, MHT, and MHS component-by-component. If there are hardware differences beyond software and calibration—such as different torque converters, valve bodies, pumps, clutch packs, or internal parts—I plan to publish a follow-up article with those findings. I think that's where we'll finally get definitive answers on what really separates these transmission variants.