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Tech Tip: GM Duramax Diesel Fuel Filter Replacement Problems

November 8, 2007

The following tip applies to all 2001-’06 General Motors trucks equipped with the 6.6L Duramax Diesel engine, RPO LB7 or LLY. There are a couple of issues with the fuel filters on these vehicles. GM has released a revised fuel filter; see TSB 04-06-04-070. The new filter is longer than the original filters used and has a plastic housing.

Note: The increased length does not change the replacement interval for the filter.

Both styles of filters include a rubber grommet located in the top of the filter. When removing an old filter, ensure this rubber grommet comes off at the same time. It’s hard to see in the vehicle and may get stuck on the filter adapter, which will not allow the replacement filter to be installed. The new style filter has a smaller inlet with a different grommet. Comparing the two, you might think you have the wrong filter, but it is correct. See Photo 1.

The other issue with the fuel filter system is that the water-in-fuel (WIF) sensor located at the bottom of the filter is made of plastic and is easily damaged while trying to remove or install it onto the filter. You should always remove the sensor and filter as a unit from the vehicle and then transfer it to the new filter.

Install the WIF sensor to the filter, only tightening it by hand. Tighten it to the point where the sensor sealing gasket just contacts the filter. Use a permanent marker and make an index mark on the sensor and the filter. Then, turn the WIF sensor an additional half turn. Once again, only tighten by hand. Do not use pliers or other tools to tighten the sensor. The replacement fuel filter should include a new seal for the sensor.

If the WIF sensor will not seal properly to the new filter, it may have been damaged during a previous filter change and you will experience a leak situation. If the WIF sensor will not tighten correctly, it will need to be replaced.

Courtesy of Nick Taylor, administrator, Mitchell 1

For more information on Mitchell 1 products and services, automotive professionals can log onto the company's website at

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