Overview
Modern trucks rely on DEF (Diesel Exhaust Fluid) systems to stay compliant and keep fleets running clean. When a DEF coolant line fails, the truck can quickly develop fault codes, derate, or end up out of service. That’s exactly what happened during a recent call to RMTC.
Customer Concern
The driver noticed warning lights related to the emissions system and experienced a loss of performance. They safely pulled over and called RMTC for help before the vehicle derated further.
Breakdown Location
The unit was stopped at a truck-friendly parking area along a major route, allowing our mobile technician to reach them quickly.
Diagnosis
Upon arrival, our technician:
- Reviewed the fault codes displayed in the dash.
- Performed a visual inspection of the DEF tank, lines, and components.
- Identified a broken DEF coolant line that was leaking and preventing proper temperature control of the DEF system.
The broken line risked triggering more severe fault codes and an eventual power derate.
Repair Story
To get the truck back on the road:
- The tech safely depressurized the system and contained any fluid.
- Removed the damaged DEF coolant line section.
- Installed a replacement line and proper clamps/fittings to OEM specifications.
- Checked for additional damage or leaks in the surrounding components.
- Cleared any inactive fault codes (if applicable) after verifying system integrity.
- Ran the engine and monitored DEF system operation to confirm stable performance.
Result for the Customer
The quick diagnosis and repair prevented a full derate and avoided an unscheduled tow or extended downtime, keeping the load on schedule.
Before
Active emissions warnings, performance concerns, and visible damage to the DEF coolant line.
After
New coolant line installed, no active leaks, and the vehicle operating normally without additional emissions faults.
