Will a 0674 Code Cause Poor MPG in a Duramax

The OBD-II diagnostic trouble code 0674 is specific to certain Duramax diesel engine models, and it refers to a potential issue with the glow plug control module. While this code alone may not directly cause poor fuel efficiency, it can have an indirect impact on mpg due to the potential side effects it may have on the engine's overall performance. The glow plug control module is responsible for regulating the heating of the glow plugs, which are crucial components in the diesel ignition system. If a fault is detected within this module, it can lead to difficulties in starting the vehicle, reduced engine power, and even potential misfires. These issues can contribute to lower fuel efficiency as the engine may have to work harder to compensate for the malfunctions. It’s important to address the underlying cause of the code and have it properly diagnosed and repaired to ensure optimal performance and fuel economy of the Duramax diesel engine.

What Is Wrong With 6.6 Duramax Fuel?

These cracks allow air to enter the fuel system, leading to reduced fuel flow and potential engine damage. The fuel filter housing isn’t designed to handle the high pressure from the injection pump, causing frequent failures and the need for costly repairs. Additionally, the 6.6 Duramax has been associated with injector failures, which can result in rough idling, decreased fuel efficiency, and even engine misfires.

Over time, the wiring harness that connects to the fuel injectors can rub against various components within the engine compartment. This constant friction can cause the insulation to wear off, exposing the wires and resulting in electrical shorts or poor connections. These issues can lead to a loss of power, uneven engine performance, and even complete engine shutdown.

Another problem with the 6.6 Duramax fuel system is the potential for water contamination. Older model years, especially those prior to 2012, are prone to water in the fuel, which can cause serious damage to the injectors and other engine components. Water can enter the fuel system through poorly sealed fuel caps or from condensation within the fuel tank, leading to decreased fuel efficiency, engine hesitation, and potential engine damage.

Additionally, the 6.6 Duramax fuel system is notorious for it’s complex design, which can make repairs and maintenance time-consuming and costly. The high-pressure fuel system requires special tools and expertise to properly diagnose and fix issues. This can result in increased repair costs and longer wait times for repairs, negatively impacting the overall ownership experience.

It’s important for owners of vehicles equipped with this engine to be aware of these issues and take necessary precautions to prevent or address them.


In conclusion, the impact of a 0674 code on the fuel efficiency of a Duramax vehicle can be variable and dependent on several factors. While it’s plausible that certain issues related to this code, such as fuel injector malfunctions or electrical problems, could contribute to poor mpg, it’s essential to consider the overall condition of the vehicle, driving habits, and other potential underlying causes. A comprehensive diagnostic evaluation performed by a qualified technician is recommended to accurately identify and address the root cause of any fuel efficiency concerns, ensuring optimal performance and longevity of the Duramax engine.

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