Diesel Engine DEF Lines Not Thawing in Cold Weather
Fault Codes & Symptoms
Active fault for DEF line heater circuit after cold soak. Related symptoms: - Engine derate. - Inducement warnings on the dash. - Inability to reset SCR faults. Machine derated overnight. It was fine when parked. Fault code for the DEF heater is active.
Confirmed cause: The DEF line heater return wire was broken inside the main chassis harness due to chafing against a steel bracket. Repair performed: Spliced in a new section of wire using environmentally-sealed butt connectors to repair the broken return wire. Secured the harness away from the bracket using a P-clamp to prevent future chafing. Verification: Cleared fault codes. Allowed the machine to cold soak. Started the engine from cold in sub-freezing temperatures. The fault code did not return, and the system thawed the DEF lines as expected. Technician notes: - The chafe point was not obvious and required removing other components to gain a clear view of the harness routing. - This fault prevents the DEF lines from thawing, which will lead to a derate and eventual shutdown in cold weather. - Always check harness routing near sharp edges or high-vibration areas.