The Engine Starter Mode parameter, Suspect Parameter Number (SPN) 1675, is a critical diagnostic signal broadcast by the Engine Electronic Control Unit (ECU) to report the current state of the starting system. This parameter is not a measurement of a physical quantity like temperature or pressure; rather, it is a 4-bit status indicator that encodes the specific phase of the engine starting sequence. It is generated by the engine ECM on virtually all heavy-duty diesel engines adhering to the SAE J1939 standard, including those from Cummins (e.g., ISX15, X15), Detroit Diesel (DD13, DD15, DD16), PACCAR (MX-11, MX-13), Volvo (D11, D13, D16), and Caterpillar (C7, C9, C13, C15, C18). For technicians and diagnostic engineers, SPN 1675 is indispensable for understanding why an engine fails to start. A simple “crank-no-start” condition can stem from a locked-out starter, an incomplete engagement, or a failure to disengage, and this SPN provides the precise state to differentiate these scenarios, saving significant diagnostic time.
Technical Overview
From an engineering perspective, SPN 1675 is a software-derived parameter, not a direct sensor input. The ECM determines the starter mode by monitoring the state of the starter relay control circuit, the engine speed sensor (crankshaft position), and the ignition key switch position. The ECM typically controls a starter relay driver (a high-side or low-side switch) that energizes the starter solenoid. When the key is turned to the “start” position, the ECM receives a digital input (typically a 12V or 24V signal) on a dedicated start request pin. The ECM then checks several interlock conditions before commanding the starter relay to engage. The four-bit binary code is constructed by the ECM’s software logic based on these inputs. For example, a value of 0010b (binary “2”) indicates the starter relay is active and the ECM has confirmed, via a rapid rise in engine speed, that the pinion gear has engaged the flywheel ring gear. A value of 0101b (binary “5”) indicates that a start was requested but the ECM has inhibited the starter because the intake air heater or glow plug cycle (preheating) is not yet complete. The normal operating range for this parameter is the full set of defined states (0 to 7), but a properly functioning engine will cycle through states 1, 2, and 3 during a successful start, returning to 0. There is no analog voltage signal; the data is purely digital, transmitted as a single byte within a larger CAN message.
J1939 Network Behavior
SPN 1675 is transmitted as part of the Electronic Engine Controller 1 (EEC1) Parameter Group, which is assigned Parameter Group Number (PGN) 61444 (0xF004). This is a high-priority, periodically broadcast message. The EEC1 message is transmitted by the engine’s primary ECU (source address typically 0x00) at a rate of approximately 10 to 50 milliseconds (10-50 Hz) when the engine is running or during a crank event. The Engine Starter Mode data occupies bits 1-4 of the first data byte (Byte 1) of the 8-byte PGN 61444 message. Other ECUs on the J1939 network, such as the transmission controller (TCM), body controller (BCM), or instrument cluster, use this information for several purposes. For instance, a TCM from Allison or ZF will monitor SPN 1675 to prevent a transmission shift command during a starter engagement (value 2). The instrument cluster may use a value of “starter active but not engaged” (value 1) to illuminate a specific warning lamp or display a “cranking” icon. The network behavior is defined such that if the ECM detects a loss of communication with the start relay circuit, it may set the starter mode to a default “inhibited” state, preventing a potentially dangerous starter motor engagement.
Diagnostic Importance
Fault codes associated with SPN 1675 are of the highest diagnostic importance because they directly relate to the engine’s ability to start and the integrity of the starting system. A failure in this system can leave a vehicle stranded. The ECM activates several engine protection strategies when a fault is detected. For example, if the ECM sees a “starter active and engaged” (value 2) for an abnormally long period (e.g., more than 30 seconds), it will de-energize the starter relay to prevent overheating and destruction of the starter motor. This is a common protection strategy found on Cummins and Detroit Diesel engines. If the ECM detects a “starter active but not engaged” (value 1) without a corresponding rise in engine speed, it will typically set a diagnostic trouble code (DTC) indicating a “starter engagement fault” and may inhibit further start attempts to prevent mechanical damage to the starter drive or flywheel. Ignoring active fault codes for SPN 1675 can have severe consequences: a continuously engaged starter can overheat, weld its contacts, or cause a ring gear failure. A “starter inhibited due to engine already running” (value 4) state that is triggered erroneously can be caused by a faulty engine speed sensor, leading to a no-start condition that is difficult to diagnose without this SPN.
Common Failure Patterns
Technicians encounter several distinct real-world failure patterns with SPN 1675. The most common is a “starter inhibited due to engine not ready for start (preheating)” (value 5) that never transitions to a cranking state. This is frequently caused by a failed intake air heater relay, a blown fuse for the heater grid, or a faulty engine coolant temperature sensor that incorrectly tells the ECM the engine is cold and requires a long preheat cycle. On PACCAR MX engines, a failed ambient air pressure sensor can also cause this. A second frequent pattern is a persistent “starter active but not engaged” (value 1) with no engine speed increase. This is often a mechanical issue: a worn starter drive (Bendix) that fails to throw the pinion gear into the flywheel, a seized starter motor, or a low battery voltage that cannot provide sufficient torque to the starter solenoid to fully engage. Wiring issues are also prevalent, such as a chafed wire in the starter relay control circuit causing an intermittent ground or open circuit. On Volvo D13 engines, corrosion in the 3-pin connector at the starter solenoid is a known failure point, leading to a “starter active but not engaged” code. Calibration drift is not a typical failure for this software-based parameter, but a corrupted ECM software flash can cause the starter mode logic to behave erratically, a rare but possible scenario.
Diagnostic Approach
A systematic diagnostic approach for any fault code involving SPN 1675 begins with connecting a J1939 compliant diagnostic tool, such as a Cummins INSITE, Detroit Diesel Diagnostic Link (DDDL), PACCAR Service Tool, or a generic tool like a Nexiq USB Link 2 with appropriate software. The first step is to read the active and inactive DTCs, paying close attention to the specific failure mode identifier (FMI). An FMI of 31 (condition exists) or 14 (special instructions) is common. Next, use the tool to view the live data value for SPN 1675 while attempting to start the engine. This is the most critical step. Observe if the value changes from 0 (start not requested) to 1 (starter active, not engaged) when the key is turned. If it does not change, the ECM is not seeing the start request signal; check the ignition switch, wiring, and fuse. If it changes to 1 but not to 2, measure the voltage at the starter solenoid control terminal during cranking. You should see battery voltage (12V or 24V). If voltage is present, the issue is mechanical or electrical in the starter motor itself. If voltage is absent, the fault lies between the ECM and the starter relay. Perform a resistance check on the control wire from the ECM to the relay. Reference values for a healthy circuit should be less than 1 ohm. Also, verify the engine ground strap is intact, as a poor ground can cause the starter to engage slowly or not at all. When circuit checks are normal, escalate to OEM software to perform a starter relay output test (e.g., a “Starter Relay Override” in Cummins INSITE) to force the ECM to energize the relay and verify the circuit integrity. If the ECM output tests good, but the starter does not engage, the starter motor or solenoid is the root cause.
Fault Codes for SPN 1675
FMI 0: Data valid but above normal operational range (most severe)
SPN 1675 FMI 0 indicates the Engine Starter Mode signal exceeds normal operational parameters within the Electronic Engine Controller. This fault commonly appears in construction equipment after prolonged cranking attempts or when starter relay circuits become contaminated with moisture. The ECM mon
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FMI 1: Data valid but below normal operational range (most severe)
SPN 1675 FMI 1 signals that the Engine Starter Mode data from the Electronic Engine Controller 1 is valid but below the normal operational range, indicating a stuck or missing start request. This commonly appears after a technician replaces the ECM without re-calibrating the starter mode parameters,
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FMI 2: Data erratic, intermittent or incorrect
SPN 1675 with FMI 2 indicates issues with the Engine Starter Mode, where data becomes erratic, intermittent, or incorrect. This often occurs after ECM replacements or when the starter motor has recently been serviced. For instance, technicians may encounter this fault code following a routine starte
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FMI 3: Voltage above normal or shorted high
SPN 1675 FMI 3 indicates voltage above normal in the Engine Starter Mode signal circuit. This fault commonly appears after ECM replacement when starter relay connections remain energized, or during cold weather operations when starter solenoids develop internal shorts. The ECM detects abnormally hig
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FMI 4: Voltage below normal or shorted low
SPN 1675 FMI 4 indicates the Engine Starter Mode circuit voltage is below normal or shorted low. The ECM monitors the starter mode status via discrete inputs or CAN data. When the voltage drops below the calibrated threshold, the ECM logs this fault. In practice, this code commonly appears after a f
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FMI 5: Current below normal or open circuit
SPN 1675 with FMI 5 indicates issues in the engine starter mode due to insufficient current or an open circuit. This fault is often encountered when technicians replace the ECM or during the initial phases of engine starting. Commonly, it’s noticed after a vehicle has undergone major engine work, le
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FMI 6: Current above normal or grounded circuit
Engine Starter Mode SPN 1675 FMI 6 indicates excessive current flow or grounded circuit in the starter control system managed by the Electronic Engine Controller 1. This fault commonly occurs during cold weather starts when technicians observe repeated starter engagement attempts that fail to crank
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FMI 7: Mechanical system not responding properly
SPN 1675 FMI 7 signals that the ECM detected a mechanical mismatch between commanded starter states (e.g., active but not engaged) and actual feedback. This code commonly appears after a forced DPF regeneration when the starter remains engaged briefly, or after replacing the ECM without recalibratin
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FMI 9: Abnormal update rate
SPN 1675 FMI 9 occurs when there’s an abnormal update rate in the engine starter mode, often due to ECM signal processing issues. This fault is frequently observed in scenarios where the starter motor appears to be operational, but the engine does not crank. Technicians often encounter this issue af
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FMI 11: Root cause not known
SPN 1675 FMI 11 indicates the Engine Control Module cannot determine the root cause of starter mode anomalies within the Electronic Engine Controller 1 protocol. This fault commonly emerges after ECM reflashing procedures when starter relay feedback signals become corrupted, leaving technicians with
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FMI 12: Bad intelligent device or component
SPN 1675 FMI 12 indicates the Engine Starter Mode signal from the ECM is invalid or erratic, violating the defined binary states. This fault commonly appears after a forced DPF regeneration when the starter remains engaged too long, or after replacing the ECM without proper calibration. The ECM dete
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FMI 13: Out of calibration
SPN 1675 FMI 13 indicates a calibration issue within the Engine Starter Mode, affecting the starter’s engagement phases. Technicians often encounter this fault after performing ECM calibrations or software updates. This error can prevent the engine from starting or cause intermittent starting issues
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FMI 14: Special instructions
SPN 1675 FMI 14 indicates the Engine Control Module requires special instructions for starter mode operation. This commonly occurs during complex starting sequences when the ECM detects conflicting conditions like simultaneous glow plug heating and starter engagement requests. Workshop technicians f
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FMI 18: Data valid but below normal operating range (moderately severe)
SPN 1675 FMI 18 indicates the Engine Starter Mode signal is valid but below the normal operating range. This typically occurs when the ECM detects a voltage level on the starter mode circuit that falls between the defined active states, often due to a weak pull-up or marginal ground. In practice, te
View SPN 1675 FMI 18 Diagnostic Guide →
FMI 31: Condition exists
SPN 1675 FMI 31 signals that the Engine Starter Mode parameter on the Electronic Engine Controller 1 message is reporting a persistent abnormal state, such as ‘starter inhibited due to engine not ready for start’ or ‘starter active but not engaged’. In practice, this fault commonly appears after a f