Rear Fuel Tank and Fuel Transfer Conditions

Some 2015-2018 Silverado and Sierra models and 2019 Silverado 2500/3500 and Sierra 2500/3500 models equipped with the 6.6L Duramax diesel engine (RPOs LML, L5P) and dual fuel tanks (23.5 gallon/89 liter front tank and 40 gallon/151 liter rear tank) (RPO N2N) may have poor fuel transfer or the rear fuel tank may have collapsed. (Fig. 13)


Fig. 13


These conditions may be caused by dirt and debris collecting on the top of the rear tank and plugging the vent (Fig. 14, #1), resulting in the fuel tank being pulled into a vacuum and bending the fuel tank fuel pump module. (Fig. 14, #2)


Fig. 14


If these conditions are found, replace the fuel tank and fuel pump module. Refer to Fuel Tank Fuel Pump Module Replacement in the appropriate Service Information.

In addition, to help prevent the vent from becoming plugged again, install a piece of fuel hose to the vent (Fig. 15, #1) and route it down the fuel feed line. (Fig. 15, #3) Secure the hose with zip ties. (Fig. 15, #2)


Fig. 15


Refer to Bulletin #19-NA-277 for additional information and part numbers.


– Thanks to Kevin Minor

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  1. Jemiel Pearson says:

    i have a customer now with the same issue. im glad i came across this thread.

  2. Be sure to check the front tank vent for the same issues, especially if the back tank has as much mud as the rear tank in the pictures, p2635 can set on the L5P from vent plugged in front tank (natural vent is usually the 1/4 fitting sticking out the side of the filler vent house on top of the module. Front tank can collapse just like the rear tank in the above pictures.

  3. Thanks for the feedback. GM Engineering has validated only the current procedure covered in Bulletin #19-NA-277.

  4. I have been doing this very repair for many years. It goes back way beyond 15 models on the 3500 with dual tank systems. Also customers who fill up with engine running defaults the transfer so it empties the front tank and will not transfer from rear is a very common problem.

  5. Terry Weszner says:

    Nice to see the attention to this concern and listed bulletin, 19-NA-277, the listed pics are actually the ones I sent in. It all looks good, but I will tell you just extending the hose to the side of the tank will result in a repeat situation. We used to route the hose up to the bottom of the box bed to get the inlet up high. It would take a little longer but would still pull in enough dust to plug the vent again with the same collapsed tank as a result. Currently we actually run the hose up to the front of the vehicle and put an old style in-line fuel filter into the inlet so that if that becomes plugged, just the filter can be changed. Highly unlikely for that to happen though as where we put the hose end there is very little dust/dirt.

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