Kubota SVL95-2s DEF Quality Light On, Engine Derated
Fault Codes & Symptoms
Engine derated, DEF warning light on steady. Related symptoms: - Engine will not perform a regeneration. - Inducement (derate) will not clear. - Fault codes related to "DEF Concentration" or "SCR System Abnormal." The machine was running fine, we refilled the DEF tank, and now the DEF light is on and the engine has no power. We used new DEF from a sealed jug.
Confirmed cause: Failed DEF Quality Sensor. The sensor, which is typically integrated into the DEF tank header assembly, was malfunctioning and providing an incorrect low-concentration reading to the ECM, triggering the derate. Repair performed: Drained the DEF tank. Replaced the DEF tank header assembly containing the integrated quality sensor. Refilled the tank with fresh, verified DEF from a sealed container. Performed the "DEF System Service" or "Reset" function with the manufacturer's electronic service tool to initialize the new sensor. Verification: After the repair and system reset, the DEF quality warning light extinguished. The service tool showed the DEF quality sensor reading as "Good" or in the normal range. A full regeneration cycle was initiated and completed successfully. The machine was operated under load for 30 minutes with no return of faults or derate. Technician notes: - This fault appeared immediately after a refill. The operator may have left the key on during the refill, which can sometimes cause the quality sensor to take a bad reading as the fluid level and concentration fluctuate. - Always test the fluid with a refractometer first. It is a quick test that avoids unnecessary parts replacement. - Some systems require a specific "DEF system reset" or "SCR component replacement" procedure in the service tool after replacing a sensor. Skipping this step may cause the new part to not be recognized.