Section 4
Exhaust & Aftertreatment
General Guidelines for DEF System
The installation of the DEF tank is a critical component of the SCR system. While Peterbilt does not recommend relocating
the DEF tank, there are applications and body installations that will require it. The guidelines below must be strictly
followed by any entity relocating the tank. Failure to follow the guidelines completely and accurately may result in engine
shutdown situations. Peterbilt offers a variety of DEF tank sizes to meet every application.
The DEF tank volume is regulated by the E.P.A.
Peterbilt advises against modifying the tank volume after the truck has been delivered from the factory.
•Total DEF capacity must meet or exceed 6% of the useable fuel capacity on the truck. The calculation
to determine DEF capacity is:
Minimum DEF Tank Volume = Useable Fuel Capacity (gal) x 0.06.
Example: For a truck with 45 useable gallons of fuel, the equation is:
DEF required = 45 x 0.06 = 2.7 gallons or more of DEF.
PACCAR-approved DEF hoses are required when retrofitting for system to function properly. The use of unapproved
hoses for DEF lines will void warranty and may cause engine shut down situations. The DEF pump (or Supply Module)
cannot be relocated from the DEF tank. In addition, the Medium Duty Rectangular DEF Tank that is used to meet clear
back of cab requirements cannot be relocated.
Installation Requirements and Dimensions for DEF System
When relocating any DEF system components, the locations must meet the guidelines below. Failure to comply may result
in non-conformance to EPA standards and engine shutdown.
DEF piping relative heights: In order to ensure proper functionality of DEF system, the height differences in the guidelines
below must be followed during line routing and component placement.
When relocating the components the maximum pressure DEF hose length from Supply module to Dosing Module is 3
meters (118”).
Maintain a minimum of 3” (76mm) clearance to shielded exhaust components when routing DEF lines to prevent possible
melting. If the DEF tank is relocated the coolant lines will need to be modified. During this process, if the tank is moved
forward on the chassis (ie closer to the engine), it is necessary to remove excess coolant lines and maintain the original
routing path. If the tank is moved rearward on the chassis, the additional length of the cooling line required to complete the
installation must be installed in a straight section of the existing coolant routing lines. This process will minimize the
change in coolant flow by minimizing changes in restrictions. Increase in restriction occurs with excessive line length and
bends. Work with your local Peterbilt dealer if you are unsure about the coolant line modifications.
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