Diagnostic Overview
Mack fault code P103C is commonly associated with SCR/NOx conversion testing or aftertreatment performance on Mack/Volvo platforms. It may appear with SCR efficiency, DEF dosing, or NOx sensor faults and can contribute to emissions warnings or derate logic. The code should be interpreted with the full active-code list and Tech Tool test results.
Likely Causes
NOx sensor issue; DEF dosing problem; SCR efficiency concern; contaminated DEF; exhaust leak; software/calibration-specific aftertreatment fault.
What To Check First
Check related NOx and SCR codes, run DEF dosing and NOx conversion tests, inspect for exhaust leaks, and verify DEF quality.