SPN 1761 FMI 18 – DEF Tank Level 1 - Empty
This code indicates that the DEF tank level is detected as empty. It’s crucial to differentiate between a true empty condition and a sensor or circuit fault.
What This Code Actually Means
The circuit logic involves the DEF level sensor sending a signal to the ECM. If the voltage from the sensor falls below a certain threshold (typically around 0.5V), the ECM interprets this as an empty tank condition. Check for proper power and ground at the sensor.
What It Does NOT Mean
This code does not necessarily mean the DEF tank is actually empty. It could also indicate a malfunctioning sensor or wiring issue.
Common Real-World Causes on Freightliner Cascadia
- Faulty DEF level sensor.
- Wiring issues, such as shorts or opens in the harness.
- Corrosion or poor connections at the sensor or ECM.
- DEF contamination or crystallization affecting sensor readings.
How the Truck Typically Acts
When this fault occurs, you may notice a warning light on the dash, and the truck may enter a reduced power mode or derate if the system believes the DEF is empty.
Step-by-Step Diagnostic Approach
- Check the DEF tank level manually to confirm it’s not empty.
- Inspect the wiring and connectors for damage or corrosion.
- Verify power and ground at the DEF level sensor.
- Test the sensor’s output voltage; it should change with the DEF level.
- If necessary, replace the sensor and clear the fault code.
Can You Keep Driving?
It’s not advisable to keep driving if this code is active, as it can lead to derate conditions and potential engine shutdown.
Shop Tip
Always inspect the DEF system for contamination before replacing any components; it can save time and unnecessary parts costs.
