A 2014 Hino 195 box truck with 61,000 miles experienced a DEF (Diesel Exhaust Fluid) system malfunction, triggering a warning light and limp mode. After draining and refilling the DEF tank, the limp mode was resolved, but the warning light persisted. After driving another 200-300 miles, the truck re-entered limp mode.
The Hino dealership diagnosed the issue using their diagnostic equipment and found fault codes related to the SCR (Selective Catalytic Reduction) system and NOx (Nitrogen Oxides) sensor. A DEF doser quantity and leak test revealed a failed leak test and excessive doser quantity. Initially, there were no visible crystallization deposits in the decomposition tube. The recommended course of action was to replace the DEF doser and perform a regeneration to monitor NOx levels.
Two parts were replaced, including the DEF injector assembly, at a cost of $1,400. However, after driving 45 miles, the DEF warning light reappeared, and the truck began losing power again. Upon returning to the dealership, preliminary findings suggested a potential problem with the DEF sprayer or misters. Further diagnosis is pending.
Understanding the 2014 Hino 195 DEF System
The DEF system in a 2014 Hino 195 is crucial for emissions control. It injects DEF into the exhaust stream, where it reacts with harmful NOx emissions, converting them into harmless nitrogen and water vapor. This process helps the truck meet environmental regulations.
Several components work together in the DEF system:
- DEF Tank: Stores the DEF fluid.
- DEF Pump: Delivers DEF from the tank to the doser.
- DEF Doser: Precisely meters the amount of DEF injected.
- DEF Injector: Sprays DEF into the exhaust stream.
- SCR Catalyst: Facilitates the chemical reaction between DEF and NOx.
- NOx Sensors: Monitor the levels of NOx in the exhaust.
Potential Causes of Recurring DEF Issues in a 2014 Hino 195
While the initial diagnosis and repair focused on the DEF doser, the recurring issue suggests other potential problems:
- Faulty DEF Sprayer/Misters: If the sprayers are clogged or malfunctioning, DEF may not be properly atomized and injected, hindering the SCR process.
- Wiring or Connector Issues: Damaged wiring or loose connections can disrupt communication between system components, leading to malfunctions.
- DEF Quality: Contaminated or low-quality DEF can damage system components and cause performance issues.
- Software Glitches: Issues with the engine control module (ECM) or other software could be contributing to the problem.
Next Steps for Troubleshooting
Further diagnostics are necessary to pinpoint the root cause of the recurring issue. This may involve:
- Thoroughly inspecting the DEF sprayer/misters for clogs or damage.
- Checking all wiring and connectors for damage or loose connections.
- Testing the DEF quality.
- Inspecting and potentially replacing the NOx sensor.
- Updating or reflashing the ECM software.
A systematic approach to troubleshooting is essential to avoid unnecessary part replacements and ensure a lasting repair.
The owner is seeking a solution that addresses the root cause of the problem to avoid recurring repairs and costly downtime. Continued diagnostics and a comprehensive understanding of the 2014 Hino 195 DEF system are crucial for resolving this issue.
