Component Location: SPN 4334 involves the DEF dosing pressure circuit. Relevant components and their general locations are: 1. DEF Supply Pump / DEF Module: Typically integrated into or mounted directly on the DEF tank. The DEF tank is usually located on the driver-side or passenger-side frame rail, rear of the cab or ahead of the rear axle, depending on the truck OEM and body configuration. On some platforms (e.g., Cummins with an Eberspächer or Bosch dosing module), the DEF pump module is a separate unit mounted near the frame rail or on the firewall area. 2. DEF Pressure Sensor: Located on the DEF dosing unit or inline on the DEF supply line between the pump and the doser valve. Exact location varies by platform — on Cummins X15/ISX15, it is typically part of the DEF dosing unit assembly. On Detroit DD13/DD15, it is part of the aftertreatment DEF pump module. 3. DEF Doser Injector: Mounted directly in the exhaust pipe in the aftertreatment system, upstream of the SCR catalyst. Typically on the driver side of the chassis, integrated into the DEF decomposition tube (mixing section). Location on the exhaust varies significantly by truck OEM and chassis configuration. 4. DEF Supply Lines: Run from the DEF tank/pump module to the dosing unit along the frame rail, typically routed with heat shielding or coolant-heated jackets. Note: Component locations vary significantly between truck OEMs (Freightliner, Kenworth, Peterbilt, Volvo, Mack, International) and engine families. Always reference the chassis-specific and engine-specific service documentation to locate these components before beginning physical inspection. Based on: general DEF system architecture knowledge confirmed across multiple platforms.