The SAE J1939 Suspect Parameter Number (SPN) 2623, known as “Accelerator Pedal #1 Channel 2,” is a critical parameter that monitors the second sensor output of a redundant-style accelerator pedal position sensor. This parameter provides a ratio of the actual accelerator pedal position to the maximum pedal position, which is essential for powertrain demand determination. It is also used for anticipatory transmission control and Anti-Slip Regulation (ASR) algorithms. SPN 2623 is commonly generated by heavy-duty engines and machinery utilizing sophisticated electronic control systems, such as those from Cummins, Detroit Diesel, and Volvo. By monitoring this parameter, technicians can gain valuable insights into driver inputs and vehicle performance, making it a vital component in the diagnostic process.
Technical Overview
SPN 2623 is measured by the Engine Control Module (ECM) using a redundant accelerator pedal position sensor, which typically contains two separate sensing elements for increased reliability. The sensor outputs an analog voltage signal that corresponds to the pedal position. This voltage is then converted to a digital signal by the ECM and transmitted over the CAN bus as a percentage of the maximum pedal position. The normal operating range for SPN 2623 is 0% to 100%, where 0% represents no pedal depression and 100% represents full pedal depression. The use of a redundant sensor design helps ensure accuracy and reliability, providing a fail-safe mechanism in case one channel fails.
J1939 Network Behavior
On the J1939 CAN bus, SPN 2623 is transmitted as part of the Parameter Group Number (PGN) for the Electronic Engine Controller 15. The transmission rate for this PGN is typically set at a frequency that balances the need for timely updates with network bandwidth considerations. The source address for this data is usually associated with the ECM, which is responsible for collecting and broadcasting the sensor information. Other Electronic Control Units (ECUs) on the network, such as those controlling the transmission and ASR systems, use this data to make informed decisions about gear selection and traction control, respectively. The precise transmission rate and source address may vary depending on the manufacturer and vehicle architecture.
Diagnostic Importance
Faults in SPN 2623 are critical as they directly affect the vehicle’s powertrain response and safety systems. If the ECM detects a discrepancy between the two channels of the redundant sensor, it may trigger a fault code and activate engine protection strategies. These strategies can include reduced engine power or limited vehicle speed to prevent potential hazards. Ignoring active fault codes related to SPN 2623 can lead to unpredictable vehicle behavior, compromised safety, and increased wear on mechanical components due to improper powertrain control. Therefore, timely diagnosis and resolution of issues related to this parameter are essential to maintaining vehicle performance and safety.
Common Failure Patterns
Technicians frequently encounter several failure patterns associated with SPN 2623. Wiring issues, such as open circuits, short circuits, or poor connections, are common culprits that can disrupt the signal from the accelerator pedal sensor to the ECM. Sensor degradation over time due to environmental factors, such as heat and vibration, can also affect performance. Contamination from dust, moisture, or other foreign substances can lead to erratic sensor readings. Calibration drift, where the sensor output gradually deviates from the actual pedal position, may occur in some cases. Mechanical failures within the pedal assembly, such as binding or wear, can also impact sensor performance.
Diagnostic Approach
The diagnostic process for SPN 2623 involves several steps. Technicians should begin by using a diagnostic scan tool capable of reading J1939 fault codes to identify any active or stored codes related to the accelerator pedal position sensor. Visual inspection of the pedal assembly and wiring harness should be conducted to check for physical damage or loose connections. Multimeter testing can verify the integrity of the circuit by measuring voltage and continuity. Reference values from the manufacturer’s service documentation should be used to compare against observed readings. If the issue persists, OEM diagnostic software may be required for advanced troubleshooting, calibration, or sensor replacement. Escalation to OEM support may be necessary if the fault cannot be resolved using standard diagnostic procedures.
Fault Codes for SPN 2623
FMI 0: Data valid but above normal operational range (most severe)
Channel 2 of accelerator pedal position sensor #1 reports values exceeding normal operational parameters, typically above 100% position. This fault commonly appears after cab replacement or pedal assembly maintenance when sensor calibration is improper. The ECM detects this condition when the second
View SPN 2623 FMI 0 Diagnostic Guide →
FMI 1: Data valid but below normal operational range (most severe)
This fault indicates that the voltage from Accelerator Pedal #1 Channel 2 (redundant sensor) is below the normal operational range, typically less than 0.5 V. The ECM detects a rationalization error between Channel 1 and Channel 2 signals. Commonly seen after a pedal replacement if the sensor is not
View SPN 2623 FMI 1 Diagnostic Guide →
FMI 2: Data erratic, intermittent or incorrect
SPN 2623 FMI 2 indicates an erratic or intermittent signal from the second output of the accelerator pedal sensor. This fault commonly appears when a vehicle experiences inconsistent throttle response, often after a forced DPF regeneration. Technicians frequently encounter this code post-ECM replace
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FMI 3: Voltage above normal or shorted high
SPN 2623 FMI 3 occurs when the voltage from Accelerator Pedal #1’s second sensor channel exceeds normal levels, indicating a short circuit. This fault often arises in vehicles after an improper wiring repair or when moisture infiltrates electrical connectors, causing signal interference. Technicians
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FMI 4: Voltage below normal or shorted low
SPN 2623 FMI 4 indicates the ECM detects voltage below the normal operating range on Accelerator Pedal #1 Channel 2 (redundant sensor output). This fault commonly appears after a forced DPF regeneration when the pedal is not released fully, or when wiring chafes against the engine block near the ped
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FMI 5: Current below normal or open circuit
This fault indicates the redundant accelerator pedal sensor channel 2 has insufficient current or open circuit condition. Technicians commonly encounter this code after cleaning throttle bodies when water infiltrates connector pins, causing intermittent signal loss. The ECM monitors dual sensor outp
View SPN 2623 FMI 5 Diagnostic Guide →
FMI 6: Current above normal or grounded circuit
SPN 2623 FMI 6 indicates an excessive current draw or a short-to-ground on the Accelerator Pedal #1 Channel 2 sensor circuit. This redundant sensor provides a secondary voltage signal to the ECM for torque and transmission control. Technicians frequently encounter this fault after a forced DPF regen
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FMI 7: Mechanical system not responding properly
SPN 2623 FMI 7 refers to a mechanical system not responding properly, specifically the second output of a redundant accelerator pedal sensor. This issue affects powertrain demand and anticipatory data for transmission and ASR systems. A common scenario where this fault appears is after replacing the
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FMI 8: Abnormal frequency, pulse width or period
SPN 2623 with FMI 8 is associated with abnormal frequency, pulse width, or period in the second output of a redundant accelerator pedal sensor. This fault often appears after replacing the ECM without recalibrating the pedal position sensor. Such issues can lead to incorrect engine power requests an
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FMI 9: Abnormal update rate
SPN 2623 FMI 9 indicates abnormal update rate from accelerator pedal position sensor channel 2, the redundant feedback circuit used for safety validation. This fault commonly appears during cold weather operations when moisture infiltrates connector pins, causing intermittent signal dropouts. The EC
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FMI 11: Root cause not known
SPN 2623 FMI 11 indicates accelerator pedal channel 2 sensor malfunction with undetermined root cause. This fault commonly appears after engine ECM replacement when technicians encounter intermittent accelerator response issues. The redundant sensor system fails to identify whether the problem stems
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FMI 12: Bad intelligent device or component
SPN 2623 FMI 12 indicates a fault in the accelerator pedal’s second sensor output, commonly found in redundant sensor systems. This error often appears after a forced DPF regeneration or when technicians replace the ECM, leading to improper sensor calibration. The fault affects the ratio of actual t
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FMI 13: Out of calibration
SPN 2623 FMI 13 indicates accelerator pedal channel 2 redundant sensor is out of calibration, causing signal deviation from factory parameters. This fault commonly appears after ECM replacement or pedal assembly service, when technicians forget to perform mandatory calibration procedures using manuf
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FMI 14: Special instructions
SPN 2623 FMI 14 signals that the ECM has received a special instruction for Accelerator Pedal #1 Channel 2, typically during a calibration routine or after a sensor replacement. This code often appears when a technician performs a forced pedal learn procedure without completing the required validati
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FMI 18: Data valid but below normal operating range (moderately severe)
SPN 2623 FMI 18 reflects a condition where the secondary output from the accelerator pedal’s redundant sensor is below its normal operating range. This issue often arises following ECM replacement or when a vehicle undergoes significant electrical system modifications. The fault impacts powertrain d
View SPN 2623 FMI 18 Diagnostic Guide →
FMI 31: Condition exists
This fault indicates the ECM has detected a persistent condition affecting the second channel of accelerator pedal position sensor #1. Modern heavy-duty vehicles use dual-channel accelerator pedal sensors for redundancy and safety validation. Technicians commonly encounter this code after cab wiring