Low DEF Pressure FIX 

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In this video we're looking at the Pressure Relief Valve in a GHG14 and GHG17 Detroit Diesel Powered Truck. We'll be talking about how to change them and why it needs to be done from time to time. One of the most common issues is a check engine light from Fault Code SPN 4374 FMI 0. This seems to be very common in equipment running in cold climates.