DFM vibration

[mike finefrock]

2020 GMC Sierra 1500 w/5.3 and 10 speed.  

Hello,

I have noticed a distinct vibration felt in the seat and on the floor when RPM's are very low.  I had it at the dealer and got what everyone else seems to get on this forum.  "Normal 'feature' for the truck with DFM... "  Since then the weather has turned colder and the truck does not get up to operating temperature quite as quickly.  Now that i drive farther with the coolant temperature in the 170° to 185° F range, I noticed that the vibration is completely gone at this temperature but when it does get to normal temp, the vibration comes back.  I think I can tell that the DFM is still working based on the MPGs.  I was thinking about changing the thermostat to a slightly cooler one.  thoughts?

Edited November 16, 2023 by mike finefrock
update

[newdude]

2 hours ago, mike finefrock said:

2020 GMC Sierra 1500 w/5.3 and 10 speed.  

Hello,

I have noticed a distinct vibration felt in the seat and on the floor when RPM's are very low.  I had it at the dealer and got what everyone else seems to get on this forum.  "Normal 'feature' for the truck with DFM... "  Since then the weather has turned colder and the truck does not get up to operating temperature quite as quickly.  Now that i drive farther with the coolant temperature in the 170° to 185° F range, I noticed that the vibration is completely gone at this temperature but when it does get to normal temp, the vibration comes back.  I think I can tell that the DFM is still working based on the MPGs.  I was thinking about changing the thermostat to a slightly cooler one.  thoughts?

 

 

Its something else that sounds like its causing this. 

 

Have a read of this PI - MC-10171305-9999.pdf (nhtsa.gov)  on 2019-2020 for DFM vibration at low RPM.  GM has found the transmission mount causing this, and the description in there matches your description quite well.

 

MC-10171305-9999.pdf (nhtsa.gov)

[mike finefrock]

Thank you for the reply.

I found that bulletin and I did inspect the mount myself but I did not remove it.  I did not see any debris.

[newdude]

1 hour ago, mike finefrock said:

Thank you for the reply.

I found that bulletin and I did inspect the mount myself but I did not remove it.  I did not see any debris.

 

 

I'd start with having the dealer run the PICOScope on it and diagnose the vibration.  

Edited November 16, 2023 by newdude