The Suspect Parameter Number (SPN) 6985, labeled “Tire Configuration Information,” plays a crucial role in modern vehicular diagnostics. It is primarily utilized in systems that require precise tire configuration data to optimize vehicle performance, safety, and fuel efficiency. This parameter is often associated with heavy-duty trucks and machinery from manufacturers such as PACCAR, Volvo, and Caterpillar, where accurate tire configuration is essential for maintaining optimal load distribution and traction control. In real-world applications, SPN 6985 is critical in scenarios such as changing tire sizes or types, which can significantly affect vehicle dynamics and performance metrics.
Technical Overview
SPN 6985 is managed through the vehicle’s Electronic Control Module (ECM), which is responsible for coordinating various subsystems to ensure accurate tire configuration settings. The parameter is initiated as a command rather than a continuous sensor measurement. It is typically transmitted as a digital message over the Controller Area Network (CAN) bus, specifically conforming to the SAE J1939 protocol. The ECM interprets the command, which can result in different operational states: ‘Take No Action,’ ‘Reset,’ ‘Reserved,’ or ‘Not Applicable.’ The parameter operates without a specific unit of measurement (denoted as nan), as its role is to instruct the system to reconfigure tire settings rather than convey a measurable physical quantity.
J1939 Network Behavior
Within the J1939 network, SPN 6985 is transmitted as part of a Parameter Group (PG) designated for reset commands. The associated Parameter Group Number (PGN) provides a structured format for ensuring the data is correctly interpreted by receiving Electronic Control Units (ECUs). The transmission rate of this SPN depends on the vehicle’s specific configuration and operational conditions but is typically event-driven, meaning it is transmitted when a change in tire configuration is required. The source address identifies the originating ECU, typically the central ECM, which manages the command dissemination. Other ECUs, such as those managing the anti-lock braking system (ABS) or traction control, utilize this data to appropriately adjust their operational parameters in response to changes in tire configuration.
Diagnostic Importance
Faults in SPN 6985 can have significant implications for vehicle safety and performance. An incorrect tire configuration may lead to uneven tire wear, reduced fuel efficiency, and compromised handling. The ECM may activate engine protection strategies such as limiting vehicle speed or torque output to prevent damage or unsafe driving conditions. Ignoring active fault codes related to this parameter can result in long-term mechanical issues and increased operational costs. Therefore, addressing faults promptly ensures that the vehicle maintains its designed performance standards and safety margins.
Common Failure Patterns
Technicians frequently encounter several common failure scenarios associated with SPN 6985. Wiring issues, such as broken or corroded connections, can result in faulty command signals being sent or received. Sensor degradation, although less common for a command parameter, can affect related components that rely on accurate tire data. Contamination from environmental factors like dust or moisture may also impact the integrity of electronic components involved in executing the tire configuration command. Calibration drift, where the system’s baseline configuration shifts over time, can lead to discrepancies between intended and actual tire settings, necessitating recalibration.
Diagnostic Approach
Diagnosing faults related to SPN 6985 involves a systematic approach. Technicians should first use diagnostic tools capable of interfacing with the J1939 CAN bus to retrieve fault codes and assess the parameter’s status. Circuit checks are essential to verify the continuity and integrity of wiring associated with the ECM and involved ECUs. Reference values for tire configuration settings should be consulted from manufacturer-specific service documentation, such as those provided by Cummins or Detroit Diesel. If initial diagnostics do not resolve the issue, escalation to OEM software may be necessary for advanced troubleshooting and reprogramming of the ECM or other affected modules. Proper documentation of changes and recalibrations is crucial to maintaining a complete service history and ensuring ongoing reliability.
Fault Codes for SPN 6985
FMI 0: Data valid but above normal operational range (most severe)
This fault occurs when the ECM receives a tire configuration reset command (PG Reset) with a value of 01b, but the signal amplitude or duration exceeds the calibrated operational window. In practice, technicians often see this after a forced DPF regeneration when the ECM attempts to reconcile tire c
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FMI 1: Data valid but below normal operational range (most severe)
SPN 6985 FMI 1 indicates a severe issue with tire configuration data being valid but below normal operational range. This is often encountered when technicians attempt a tire configuration reset but encounter unexpected results. A real-world scenario includes after replacing tires with different spe
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FMI 2: Data erratic, intermittent or incorrect
SPN 6985 FMI 2 indicates erratic or intermittent data in the tire configuration reset command system. This fault commonly appears during wheel replacement procedures when technicians attempt to recalibrate tire parameters after installing different tire sizes. The ECM receives inconsistent reset com
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FMI 3: Voltage above normal or shorted high
SPN 6985 FMI 3 indicates the ECM detected a voltage above normal or a short-to-high condition on the circuit responsible for the tire configuration reset command (PG Reset). This fault commonly appears after a technician mistakenly back-probes the connector with a test light during a DPF regeneratio
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FMI 4: Voltage below normal or shorted low
SPN 6985 FMI 4 signifies a voltage below normal or shorted low condition affecting tire configuration information. This fault code typically arises during maintenance procedures involving tire pressure monitoring system recalibrations, particularly after wheel alignments or tire replacements. The co
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FMI 5: Current below normal or open circuit
This fault indicates insufficient current flow in the tire configuration reset command circuit, preventing proper wheel speed sensor calibration and vehicle system initialization. Technicians commonly encounter this code after ECM replacement or when performing tire size changes, as the system canno
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FMI 6: Current above normal or grounded circuit
This fault code triggers when the ECM detects a current above normal or a grounded circuit on the tire configuration reset signal line (PG Reset). In practice, this code often appears after a technician accidentally shorts the configuration pin during a tire pressure monitoring system retrofit or af
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FMI 7: Mechanical system not responding properly
SPN 6985 FMI 7 refers to a mechanical system not responding properly during tire configuration changes. This fault often surfaces when a vehicle’s tire setup is altered, such as upgrading to off-road tires, and the ECM fails to register the new configuration. Technicians frequently encounter this co
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FMI 9: Abnormal update rate
The SPN 6985 FMI 9 fault indicates an abnormal update rate in the tire configuration information system. This issue often arises after technicians perform a tire replacement or reset the tire configuration settings. Such conditions can lead to mismatches in expected data update frequencies, causing
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FMI 11: Root cause not known
SPN 6985 FMI 11 indicates an unidentified failure in the tire configuration reset command system. This fault commonly appears after ECM software updates or when tire pressure monitoring systems fail to acknowledge configuration changes. The root cause remains unknown, requiring systematic diagnostic
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FMI 12: Bad intelligent device or component
SPN 6985 FMI 12 indicates that the Tire Configuration Information command, specifically the Reset signal (01b), has been received by the ECM but the intelligent device or component responsible for processing the configuration change has failed or is reporting an invalid state. This fault commonly ap
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FMI 13: Out of calibration
SPN 6985 FMI 13 often appears in heavy-duty vehicles after incorrect tire size input during maintenance. This fault indicates the tire configuration reset command is out of calibration, potentially affecting vehicle stability and fuel efficiency. Commonly, technicians encounter this issue when tire
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FMI 14: Special instructions
SPN 6985 FMI 14 indicates special instructions required for tire configuration reset command processing within the vehicle’s electronic control system. This fault commonly appears after tire size changes, axle reconfiguration, or ECM replacement procedures when technicians must reinitialize the vehi
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FMI 18: Data valid but below normal operating range (moderately severe)
SPN 6985 FMI 18 indicates the Tire Configuration Information reset command (01b) is being received as a ‘Take No Action’ (00b) or below normal operating range. This fault commonly appears after a tire size change or ECM replacement when the configuration message is not properly transmitted. In pract
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FMI 31: Condition exists
SPN 6985 with FMI 31 indicates a persistent condition where the vehicle’s tire configuration information requires a reset. This fault is typically encountered when there are changes in tire size, pressure, or type, necessitating an update in the electronic control module (ECM). Technicians often see