The SAE J1939 SPN 4375, labeled as “Aftertreatment 1 Diesel Exhaust Fluid Pump Drive Percentage,” monitors the command signal sent to control the speed of the diesel exhaust fluid (DEF) pump. This parameter is integral to the selective catalytic reduction (SCR) system, commonly found in engines from manufacturers like Cummins, Detroit Diesel, PACCAR, and Volvo. The DEF pump plays a critical role in the reduction of nitrogen oxides (NOx) emissions, making SPN 4375 crucial for maintaining compliance with environmental regulations. Accurate diagnostics of this parameter ensure the efficient operation of the SCR system, preventing costly repairs and maintaining vehicle uptime.
Technical Overview
SPN 4375 represents the percentage command signal sent from the engine control module (ECM) to the DEF pump motor to regulate its speed. The ECM measures this parameter using a closed-loop control system that includes feedback from the DEF pump speed sensor. The signal is typically a pulse-width modulated (PWM) signal, varying from 0% to 100%, where 0% indicates no drive and 100% indicates full drive. In normal operating conditions, the drive percentage fluctuates based on the engine load and exhaust temperature, typically ranging from 10% to 90%. This regulation ensures the precise dosing of DEF into the exhaust stream for optimal NOx conversion.
J1939 Network Behavior
On the J1939 CAN bus, SPN 4375 is part of the Parameter Group “Aftertreatment 1 Diesel Exhaust Fluid Supply Information,” transmitted using a specific Parameter Group Number (PGN). This PGN is broadcast at regular intervals, typically every 100 milliseconds, allowing other electronic control units (ECUs) to access real-time DEF pump drive information. The source address for this parameter is usually assigned to the aftertreatment control module (ACM) or the engine control module (ECM), depending on the system configuration. Other ECUs, such as the vehicle control unit (VCU) or the dashboard display, may use this data for monitoring and diagnostic purposes.
Diagnostic Importance
Faults in SPN 4375 can significantly impact engine performance and emissions compliance. When a fault is detected, the ECM may trigger engine protection strategies, such as derating power output or limiting vehicle speed, to prevent excessive NOx emissions. Ignoring active fault codes related to this parameter can lead to increased DEF consumption, catalyst damage, and non-compliance with emissions regulations. Therefore, timely diagnosis and resolution of issues with SPN 4375 are critical to maintaining engine efficiency and environmental standards.
Common Failure Patterns
Technicians frequently encounter several real-world failure scenarios with SPN 4375. Wiring issues, such as open circuits or short circuits in the DEF pump drive wiring, are common culprits. Sensor degradation, particularly in the DEF pump speed sensor, can lead to incorrect feedback and misinterpretation of pump speed. Contamination of the DEF system due to impurities in the DEF fluid can cause mechanical failures in the pump. Calibration drift in the ECM or ACM may result in incorrect drive percentage calculations. Mechanical failures, such as pump motor wear or blockages in the DEF supply line, can also affect this parameter.
Diagnostic Approach
Diagnosing faults related to SPN 4375 requires a systematic approach. Technicians should use a J1939-compatible diagnostic tool to read fault codes and monitor live data. Initial checks should include a visual inspection of the DEF pump and wiring harness for damage or corrosion. Circuit checks with a multimeter can verify the integrity of electrical connections and the presence of the correct PWM signal. Reference values from OEM service manuals, such as those from Cummins or Volvo, can guide the evaluation of sensor feedback and ECM outputs. If initial diagnostics do not resolve the issue, escalation to OEM diagnostic software may be necessary for advanced troubleshooting, including recalibration of the control module or replacement of faulty components.
Fault Codes for SPN 4375
FMI 0: Data valid but above normal operational range (most severe)
This fault code arises when the aftertreatment system commands the diesel exhaust fluid (DEF) pump to operate above normal limits. Technicians often encounter SPN 4375 FMI 0 after performing maintenance on the SCR system, where recalibration wasn’t executed properly. The ECM may drive the DEF pump e
View SPN 4375 FMI 0 Diagnostic Guide →
FMI 1: Data valid but below normal operational range (most severe)
This fault indicates the diesel exhaust fluid pump drive percentage is below normal operational range, typically under 5% command signal. Commonly occurs after DEF system repairs when pump motor brushes are worn or electrical connections are compromised. Technicians frequently encounter this code fo
View SPN 4375 FMI 1 Diagnostic Guide →
FMI 2: Data erratic, intermittent or incorrect
SPN 4375 FMI 2 indicates the ECM detects erratic, intermittent, or incorrect data from the aftertreatment 1 diesel exhaust fluid (DEF) pump drive percentage signal. This fault commonly appears after a forced DPF regeneration when the pump motor fluctuates unexpectedly, or after replacing the ECM wit
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FMI 3: Voltage above normal or shorted high
SPN 4375 FMI 3 indicates the ECM detected voltage above normal on the DEF pump drive command circuit. This fault often appears after a forced DPF regeneration when the pump runs continuously, or after replacing the ECM without recalibrating the pump driver. The ECM monitors the pump motor command si
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FMI 4: Voltage below normal or shorted low
This fault indicates the ECM detects voltage below normal threshold on the DEF pump motor drive circuit. The pump drive percentage command cannot be properly executed due to insufficient voltage supply. This code frequently appears after DEF system component replacement or during cold weather operat
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FMI 5: Current below normal or open circuit
SPN 4375 FMI 5 indicates a current below normal or open circuit in the Diesel Exhaust Fluid (DEF) Pump Drive. This fault often appears after routine maintenance when connectors are not properly reattached or wiring is inadvertently damaged. Technicians might notice this code following the replacemen
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FMI 6: Current above normal or grounded circuit
This fault indicates excessive current flow through the DEF pump motor control circuit, commonly triggered by pump motor bearing seizure or wiring harness damage. Technicians frequently encounter this code during cold weather operations when crystallized urea causes pump motor overload, particularly
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FMI 7: Mechanical system not responding properly
SPN 4375 FMI 7 indicates a malfunction in the DEF pump drive percentage, often observed post-ECM replacement or during DEF system calibrations. This fault is crucial as it impacts the exhaust fluid delivery rate, leading to improper emissions treatment. In practice, technicians may encounter this co
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FMI 9: Abnormal update rate
This fault indicates the ECM receives DEF pump motor control signals at irregular intervals, disrupting proper SCR dosing control. Technicians commonly encounter this code after ECM firmware updates or when replacing aftertreatment control modules, as the communication timing parameters may require
View SPN 4375 FMI 9 Diagnostic Guide →
FMI 11: Root cause not known
This fault indicates the ECM has detected an unknown root cause for the commanded DEF pump drive percentage signal. The pump may still receive a command, but the ECM cannot validate the actual response. Technicians often see this after replacing the ECM without proper calibration, or after a wiring
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FMI 12: Bad intelligent device or component
SPN 4375 with FMI 12 indicates a malfunction in the diesel exhaust fluid pump’s drive percentage control. This typically arises when the signal sent to the DEF pump motor is inconsistent or erroneous, often due to a faulty intelligent component. In practice, this fault commonly emerges during diagno
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FMI 13: Out of calibration
SPN 4375 FMI 13 indicates the aftertreatment diesel exhaust fluid pump drive percentage is out of calibration. This fault commonly appears after ECM replacement or software updates when the pump control parameters haven’t been properly recalibrated. The ECM cannot accurately control DEF injection ra
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FMI 14: Special instructions
SPN 4375 FMI 14 indicates the ECM has received a special instruction related to the DEF pump drive percentage, often triggered after a failed forced DPF regeneration or a software update mismatch. Technicians see this code when the pump command signal is overridden by an external tool or when a new
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FMI 18: Data valid but below normal operating range (moderately severe)
SPN 4375 FMI 18 indicates that the diesel exhaust fluid pump drive percentage is below normal operating range. This often occurs after a forced DPF regeneration, as the system recalibrates its parameters. Technicians might encounter this fault code when the ECM commands the pump to operate at a high
View SPN 4375 FMI 18 Diagnostic Guide →
FMI 31: Condition exists
SPN 4375 FMI 31 indicates an existing condition with the DEF pump drive percentage command signal. This fault commonly appears during cold weather startup when DEF crystallization occurs, or after SCR system maintenance when pump calibration parameters require reset. The ECM continuously monitors th