In most cases, exterior cleaning with deionized water and a soft cloth is sufficient. If the sensor can be serviced, use OEM-recommended methods and cleaners; if readings remain faulty after cleaning, replacing the sensor is often the most reliable option.
What a DEF level sensor does
DEF (Diesel Exhaust Fluid) level sensors monitor the amount of 32.5% urea solution in the DEF tank. They can be capacitive or float-type, and they feed data to the engine control module to prevent SCR system issues when DEF runs low. Deposits, contamination, or crystallization can cause inaccurate readings or fault codes.
Tools and safety
Gather the right tools and follow safety practices to protect yourself and the DEF system from contamination. Use only DEF-grade cleaners and avoid introducing unapproved solvents into the DEF circuit.
- Deionized or distilled water
- Lint-free, non-abrasive cleaning cloths
- Soft-bristle brush (non-metallic)
- OEM-approved cleaning solution or a mild detergent recommended by the manufacturer
- Replacement O-rings or seals (if you plan to remove the sensor)
- Basic hand tools as specified by the OEM for sensor access
- Personal protective equipment: gloves and eye protection
- Container to collect used DEF and waste water
Using the right tools helps prevent contamination and keeps the DEF system in spec. Always check the manufacturer’s guidance for compatible cleaners and procedures before starting.
Step-by-step cleaning procedure
Follow these steps to clean and inspect a DEF level sensor. Some sensors are not field-serviceable; always consult the OEM manual before disassembly.
- Identify the sensor type and review the OEM service manual to confirm whether field cleaning or removal is allowed.
- Power down the vehicle or system and ensure the DEF tank is at a safe temperature; avoid hot surfaces and splashes.
- Gain access to the sensor through the access panel or service ports as described by the manual.
- If the sensor is removable and you are permitted to remove it, disconnect the electrical connector and carefully lift the sensor from the tank; retain any seals or gaskets.
- Inspect the sensor for buildup, crystallization, or damage; note any missing O-rings or cracked housing.
- Clean the exterior sensing surfaces with a lint-free cloth dampened in deionized water; use a soft brush to remove stubborn deposits. Do not use abrasive tools or solvents not approved by OEM.
- If the OEM permits, lightly wipe any internal deposits with a cleaner recommended by the manufacturer, then rinse with DI water to remove residues; ensure the sensor is completely dry before reassembly.
- Reinstall the sensor if it was removed, reattach the electrical connector, replace seals as needed, refill DEF to the correct level, and run a system test to confirm accurate readings and no leaks.
Note: If the sensor cannot be cleaned in place or readings do not improve after cleaning, replacement is often the most reliable solution. Always follow the manufacturer's replacement intervals and standards.
When to service vs replace
A clean sensor should provide accurate readings. Consider replacement if you observe persistent faults, erratic signals, physical damage, or if the sensor is beyond repair after cleaning.
- Repeated false or fluctuating DEF level readings
- Visible damage to the sensor housing or wiring
- Persistent SCR warnings or DEF quality faults despite cleaning
- Cracked seals or signs of leakage in the sensor area
When in doubt, rely on the OEM guidance and service manuals. Replacing a faulty sensor is often more cost-effective than repeated cleaning attempts.
OEM guidance and DEF quality
DEF purity and standards
DEF must meet ISO 22241 specifications (urea concentration, purity, and water content). Use only DEF from reputable suppliers and store it in sealed, labeled containers to minimize contamination risk.
Use approved cleaners and procedures
Only use cleaners and procedures recommended by the vehicle or equipment OEM. Some sensors are not designed to tolerate certain solvents or aggressive scrubbing, which can damage seals or coatings and worsen readings.
Storage and handling
Keep DEF cold but above freezing, away from direct sunlight and contaminants. Replace DEF in the tank promptly if it appears cloudy, contains crystals, or has a strong odor.
Summary
DEF level sensors must be treated with care to maintain accuracy and SCR system reliability. In many cases, exterior cleaning with deionized water and a soft cloth is sufficient, and many sensors are not field-serviceable. Always consult the OEM service manual for disassembly, cleaning agents, and reassembly steps. If readings persistently fail after cleaning, replace the sensor. Maintaining ISO 22241-compliant DEF and proper storage practices helps prevent sensor issues and SCR faults.
How do you reset the DEF level sensor?
How do I reset the DEF light after filling the tank? After refilling the DEF tank, start the engine and drive slowly and steadily for several minutes. A few minutes of driving will recalibrate the system. If it doesn't, you may need to use an OBD-II scanner to identify the cause of the problem.
Are there additives that will clean a DEF sensor?
Use a high-quality DEF system cleaner and maintenance additive, such as Hot Shot's Secret Premium DEFender, to clean deposits and prevent future buildup. After cleaning, inspect the DEF injector and sending unit for any residual buildup that may require manual removal.
How to check if a DEF level sensor is bad?
How can I tell if my DEF sensor is malfunctioning? Signs of a malfunctioning DEF sensor may include warning lights or messages on the dashboard, reduced engine power, and increased emissions. A diagnostic scan tool can also identify specific sensor-related trouble codes.
Can you use WD-40 to clean sensors?
Number three spraying WD40 or silicone products spraying WD40 or silicone products anywhere near an oxygen sensor can cause serious. Problems inside the engine. System these sprays release oil and