91401-ZW9-000 Honda TUBE, BREATHER (Honda Code 6644389).

Introduction
Do not perform any procedure in this Special Instruction until you have read the information and you understand the information.There have been some isolated instances of issues with debris blocking up the pickup pipe for the manifold (DEF Heater). This has resulted in a lack of injection of Diesel Exhaust Fluid (DEF). The following diagnostic trouble codes may be displayed in the electronic service tool:
E931 (2) Low Aftertreatment #1 SCR Dosing Reagent Absolute Pressure: Low - moderate severity (2)
E1370 (2) Aftertreatment Diesel Exhaust Fluid Dosing Unit Loss of PrimeA new Diesel Exhaust Fluid (DEF) filter has been introduced. The new DEF filter helps to eliminate debris from entering the DEF system and reduces the occurrences of the E931 (2) and E1370 (2) diagnostic trouble codes being displayed.Safety Section
Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids.Refer to Special Publication, NENG2500, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat® products.Dispose of all fluids according to local regulations and mandates.
Illustration 1 g00104545Prevent the machine from movement. Park the machine on a level surface.Attach a "Do Not Operate" warning tag or a similar warning tag to the start switch or to the controls before you service the equipment. These warning tags (Special Instruction, SEHS7332) are available from your Caterpillar dealer.Required Parts
Table 1 contains the parts needed to complete the installation of the new DEF filter.Note: Only one DEF filter group is required per engine. Use Table 2 to determine which filter is the appropriate filter for each DEF header. Illustration 2 shows the location of the DEF header part number.
Table 1
Part Number Part Description Qty
378-3187 Diesel Exhaust Fluid Filter Gp 1
423-3251 Connector 1
391-5262 Gasket 1
425-0385 Filter As 1
452-6055 Filter Base As 1
453-1604(1) Diesel Exhaust Fluid Filter Gp 1
453-1605(1) Diesel Exhaust Fluid Filter Gp 1
453-1606(1) Diesel Exhaust Fluid Filter Gp 1
(1) Use Table 2 to choose the correct part that corresponds to the DEF header
Illustration 2 g03745839
(1) Location of DEF heater part number
Table 2
DEF Heater Part Number Required DEF Filter
434-3241 453-1604
434-3242 453-1605
434-3243 453-1606 Installation Procedure
Ensure that the area around the DEF heater is clean and free from debris.
Remove manifold DEF heater from DEF tank. Refer to Disassembly and Assembly, Manifold (DEF Heater) - Remove and Install for the correct procedure.
Illustration 3 g06013988
Typical example
Position filter base assembly (3) to DEF heater (2). Install screws (1) to filter base assembly (3). Tighten the self-tapping screws (1) securely.Note: Each half of the adapter has two small locking tabs that secure to the bottom side of the DEF heater.
Remove existing filter from the pickup pipe on manifold DEF heater. Refer to Disassembly and Assembly, Manifold (DEF Heater) - Remove and Install for the correct procedure.
Install a new filter to the pickup pipe on manifold DEF heater. Refer to Disassembly and Assembly, Manifold (DEF Heater) - Remove and Install for the correct procedure.
Illustration 4 g06013992
Typical example
Position the correct DEF filter (5) to the filter base assembly (3). Install band clamp (4). Tighten the band clamp to a torque of 4.5 N m (40 lb in).
Install manifold DEF heater to DEF tank. Refer to Disassembly and Assembly, Manifold (DEF Heater) - Remove and Install for the correct procedure.
Connect hose