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Full Diagnostic Guide — SPN 4335 FMI 1 1. What does SPN 4335 FMI 1 mean? SPN 4335 FMI 1 refers to the Aftertreatment 1 SCR Dosing Air Assist Absolute Pressure being detected below normal operational range. FMI 1 specifically indicates ‘Data Valid but Below Normal Operational Range – Most Severe Level.’ This means the … Read more

Full Diagnostic Guide — SPN 4334 FMI 7 1. What does SPN 4334 FMI 7 mean? SPN 4334 FMI 7 indicates a mechanical system non-response from the DEF doser absolute pressure sensor in the SCR dosing unit. The pressure measurement closest to the dosing valve shows abnormal behavior, often linked to inconsistent DEF injection patterns. … Read more

Full Diagnostic Guide — SPN 4334 FMI 4 1. What does SPN 4334 FMI 4 mean? SPN 4334 refers to the DEF doser absolute pressure sensor parameter. FMI 4 indicates a voltage below normal, meaning the sensor signal voltage has dropped below the expected minimum threshold, typically below 0.5 V on a 0-5 V analog … Read more

Full Diagnostic Guide — SPN 4334 FMI 3 1. What does SPN 4334 FMI 3 mean? SPN 4334 FMI 3 indicates that the Aftertreatment 1 Diesel Exhaust Fluid (DEF) Doser 1 Absolute Pressure sensor is reporting a voltage above normal or a shorted-high condition. The ECM has detected that the pressure sensor signal voltage has … Read more

Full Diagnostic Guide — SPN 4334 FMI 2 1. What does SPN 4334 FMI 2 mean? SPN 4334 FMI 2 indicates erratic pressure readings from the DEF doser absolute pressure sensor. The sensor, located near the dosing valve in aftertreatment system 1, sends inconsistent pressure data to the ECM, suggesting fluctuations outside of normal parameters. … Read more

Full Diagnostic Guide — SPN 4334 FMI 18 1. What does SPN 4334 FMI 18 mean? SPN 4334 FMI 18 indicates that the absolute pressure measured at the Diesel Exhaust Fluid (DEF) dosing unit 1 is below the normal operating range. This means the ECM has detected that the DEF pressure is too low for … Read more

Full Diagnostic Guide — SPN 4334 FMI 16 1. What does SPN 4334 FMI 16 mean? SPN 4334 FMI 16 indicates the DEF (Diesel Exhaust Fluid) doser absolute pressure sensor is reading above normal range, typically exceeding the 400–800 kPa operational threshold. FMI 16 specifically means ‘Data Valid But Above Normal Operating Range – Moderately … Read more

Full Diagnostic Guide — SPN 4334 FMI 1 1. What does SPN 4334 FMI 1 mean? SPN 4334 FMI 1 indicates that the DEF doser absolute pressure has fallen below the critical operational threshold. This prevents proper urea injection into the SCR catalyst, potentially due to issues like frozen DEF lines or pressure sensor failure. … Read more

Full Diagnostic Guide — SPN 4332 FMI 31 1. What does SPN 4332 FMI 31 mean? SPN 4332 FMI 31 indicates the Aftertreatment 1 SCR System 1 State has reported an undefined or invalid binary pattern to the ECM. Per SAE J1939, valid states are integers 0 through 7; any other value (e.g., 8 or … Read more

Full Diagnostic Guide — SPN 4331 FMI 18 1. What does SPN 4331 FMI 18 mean? SPN 4331 FMI 18 indicates that the Diesel Exhaust Fluid (DEF) dosing quantity in the Aftertreatment 1 SCR system is below the normal operating range. FMI 18 specifically means the signal or value is below normal but not low … Read more