T434814 | Genuine Cat® DEF (Diesel Exhaust Fluid) Sensor Head Assembly

Sensor Type: Digital (canbus)
DEF Header Height (IN): 11
DEF Suction Fitting Dia. (IN): 3/8 SAE J2044
DEF Return Fitting Dia. (IN): 5/16 SAE J2044
Coolant Inlet Fitting Dia. (IN): 5/8 Hose Bead
Coolant Outlet Fitting Dia. (IN): 5/8 Hose Bead
In-Tank Filter: 40µ
Tank Interface: 4.05 Dia. Bore Seal

• Monitoring DEF level
  • Measures how much DEF is available.
  • Warns the driver before the tank runs empty.
  • Helps prevent SCR system shutdown due to lack of DEF.
• Monitoring DEF quality
  • Verifies that the fluid has the proper concentration (32.5% urea and 67.5% deionized water).
  • Detects contaminated, diluted, or incorrect fluid that could damage the SCR system or reduce emissions performance.
• Monitoring DEF temperature
  • Detects when DEF is frozen or approaching its freezing point (about -11°C / 12°F).
  • Allows the vehicle to activate heaters so DEF can be used once thawed.
• Supporting emissions compliance
  • Supplies data to the engine control module, which adjusts DEF dosing into the exhaust.
  • Helps the vehicle meet emissions regulations by ensuring the SCR system operates correctly.
• Improving reliability and diagnostics
  • Provides continuous sensor data that can identify problems early.
  • Makes it easier for technicians to diagnose faults through diagnostic trouble codes (DTCs).

• DEF warning light or message appears on the dashboard.
• DEF level reads empty or very low even though you've recently filled the tank.
• DEF level doesn't change after adding fluid.
• "Poor DEF Quality" warning despite using fresh, certified DEF.
• Check Engine Light (CEL) comes on.
• Emissions system or SCR fault messages appear.
• Engine derate (reduced power) to encourage repair of the emissions system.
• Countdown to limited starts or no restart, depending on the vehicle manufacturer.
• Intermittent warnings that come and go due to an internal electrical fault.