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GM vehicles with Duramax diesel engines are reportedly malfunctioning. The models the issue affects include the Chevrolet Silverado, Tahoe SUV, and Suburban SUV. The issue is in three separate Duramax diesel engines, focusing on the diesel exhaust fluid (DEF) sensors. 

DEF sensors measure the amount of fluid in the tank. The DEF fluid helps in reducing diesel emissions and is pumped directly into the Selective Catalytic Reduction (SCR) system. Issues from the malfunction include the fluid level reading incorrectly, erratic function, and, in some cases, getting stuck. The result can lower the torque of the engines, according to GM Authority. 

Which Chevrolet Duramax diesel engines are having the issue?

The 2023 Chevy Suburban parked near a home
2023 Chevy Suburban | Chevrolet

What drivers are experiencing include a malfunction indicator light coming on, a “Service Emission System” warning, or a “DEF Level Low” message. These can happen individually or concurrently. Chevrolet has issued several technical service bulletins addressing the DEF sensor malfunctions. These cover several aspects of the problem and possible fixes. 

Below are all affected Chevrolet vehicles:

LM2 Duramax turbodiesel 3.0L I6 engine:

  • 2020 to 2022 Chevy Silverado 1500
  • 2021 to 2024 Chevy Tahoe
  • 2021 to 2024 Chevy Suburban

LZ0 Duramax turbodiesel 3.0L I6 engine:

L5P Duramax turbodiesel 6.6L V8 engine:

  • 2020 to 2024 Chevy Silverado HD

Are Duramax DEF systems problematic?

2023 Chevrolet Silverado LZ0 Duramax diesel engine on white background
2023 Chevrolet Silverado LZ0 Duramax diesel engine | GM

Diesel exhaust fluid systems are very reliable, but they can be problematic. Issues deal mostly with fluid degradation, or owner maintenance, or lack thereof. Crystallization can occur in the system from two owner errors by either overfilling the fluid or using tap water to top off the tank. Deposits form and can get into fuel injector nozzles or the exhaust. 

Crystal deposits can cause problems, but so can dirt. It acts as sandpaper inside of the DEF pump. This can be a result of poor storage or reusing DEF containers. 

Shouldn’t GM’s warranty cover this issue?

A 2023 Chevy Silverado with a diesel engine.
2023 Chevy Silverado 1500 | Chevrolet

Using tap water can also dilute the mix, affecting how well it works to lessen emissions. The fluid is sold premixed. So, adding the right amount of the mix eliminates this dilution problem. Cold weather can also have negative effects on DEF. 

The good news with all of this is that since these are 2020 to 2024 GM vehicles, the Duramax diesel engines should be under warranty. So the best thing is to take it back to the dealer. The only downside to doing this is that we have seen on some Duramax and Silverado forums sometimes owners must wait months for parts to fix DEF issues.

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Staff Writer

Thom Taylor

Thom Taylor is a celebrated automotive journalist. He was awarded the Top 100 Most Influential People in Hot Rodding from Hot Rod Magazine, and was inducted into the Grand National Roadster Show Hall of Fame and the National Rod and Custom Hall of Fame. He’s a member of SEMA and the NHRA.

Thom has authored a number of books, including Hot Rod & Custom Chronicle and several guides for drawing vehicles like a pro, which pull from his distinguished ventures as an automotive illustrator.

Thom joined the MotorBiscuit team in 2019, and focuses his coverage on new vehicle releases, design, and the latest features and tech in the industry. His tenure of 25 years writing about the industry gives him a unique context for the auto news he covers, whether it’s part of the Rusty Monday series or the latest news from Chevy. Thom has built two complete cars from the ground up and driven vintage roadsters at the Indy 500.