The DEF (Diesel Exhaust Fluid) head unit is a sensitive component responsible for measuring DEF level, temperature, and quality inside the tank. Failures are increasingly common in modern diesel vehicles and can lead to major drivability issues.
Common Causes of DEF Head Unit Failure:
- Crystallized DEF Buildup
- DEF fluid can crystallize when exposed to air, especially around the sensor and pickup tube. This buildup can clog passages or interfere with sensor function.
- Contaminated DEF Fluid
- Using dirty, expired, or non-compliant DEF (not meeting ISO 22241 standards) can damage internal sensor elements and clog filters.
- Electrical or Sensor Failure
- Internal circuit board failure, broken sensor elements, or voltage spikes can cause the unit to stop sending accurate signals.
- Water Intrusion or Corrosion
- Moisture entering the DEF tank or sensor connector area can corrode the electronics and cause intermittent or total failure.
- Freeze/Thaw Damage
- DEF freezes around 12°F (-11°C). While most systems are designed to handle this, repeated freeze-thaw cycles can degrade seals and plastics, leading to cracks or malfunction.
- Normal Wear Over Time
- Exposure to harsh environments and constant cycling can simply wear out the head unit over several years of use.
Always store and handle DEF properly, use high-quality fluid, and inspect the tank area regularly to extend the life of the DEF head unit.
