What is a Suspect Parameter Number? The CAN bus has proven to be transformational for vehicle functionality, and the Suspect Parameter Number (SPN) is an integral component, allowing easy identification and diagnosis of fault codes generated by the electronic control unit (ECU). Through these codes, we have faster, more efficient troubleshooting and more effective monitoring of vehicle processes. The Suspect Parameter Number if a diagnostic trouble code, each one is unique and it gives vital information about specific faults that a vehicle ECU has detected. It is a faster, easier approach to problem solving, explaining the area and type of issue that the vehicle is experiencing in a single piece of data. What do SPNs do? With the automotive industry embracing car technology so successfully, one of the challenges of modern vehicles that rely heavily on a variety of sensors, processors and other electronic systems, is identifying which one is causing a fault. The Suspect Parameter Numbers work as a universal language, each code representing a specific fault that is consistent across different makes and models of vehicle, to speed up the troubleshooting process. In most cases, SPNs are tied to faults reported by the ECU, so technicians can quickly discover what system is causing the issue, whether that is a fuel system, ignition, gearbox and so on. SPNs in Practice One of the most common ways this technology is used for fleet management is through telematics systems, such as AutoPi. If we place an AutoPi device to each vehicle in the fleet, they will constantly monitor suspect parameter numbers, checking for problems. To see the value of the SPN system, we can look at a real-world example using the AutoPi Device. Here, the AutoPi uses SPN numbers to identify faults, and through its real-time monitoring of vehicle health, provides detailed diagnostics of those faults for the vehicle owner or fleet manager. This includes real-time alerts for any problems that emerge as the vehicle is in use. Discover More About the Devices The system functions as follows: Feature Functionality Connection Benefit AutoPi TMU CM4 Provides detailed diagnostics and real-time monitoring Vehicle's CAN bus Enables precise fault identification and vehicle health monitoring SPN Code Reading Reads SPN codes directly from the ECU ECU via CAN bus Facilitates accurate diagnostics and troubleshooting Platform Interpretation Interprets SPN codes through AutoPi's platform AutoPi Cloud Platform Allows for easy monitoring and interpretation of vehicle data Remote monitoring Enables remote vehicle status monitoring AutoPi Cloud Offers convenience in managing vehicle health and maintenance Alerts and Maintenance Sends alerts for SPN-triggered faults AutoPi Cloud Supports proactive maintenance decisions and reduces downtime As we can see in the table, the AutoPi TMU CM4 uses the power of suspect parameter numbers to enable advanced vehicle diagnostics and condition monitoring in real time, allowing fleet managers and vehicle owners to make informed choices about vehicle use. SPNs give us valuable insights that can save both time and money, but to make the most of this data, you need the right tools to manage it in real time. That’s where AutoPi TMU CM4 comes in. It connects directly to your vehicle’s systems and reads SPN codes instantly, so you can spot and address any issues right away. Whether it's a small glitch or a potential problem, AutoPi makes sure you're always ahead of the game. AutoPi TMU CM4 not only monitors your vehicle’s health in real time, but it also sends instant alerts for any problems, giving you the chance to act before they escalate into costly repairs. For fleet managers and vehicle owners, AutoPi TMU CM4 is the ultimate tool for proactive vehicle management. With its easy-to-use platform, you don’t need to be a tech expert to understand your vehicle’s diagnostics. Just plug in AutoPi, and it takes care of the rest—providing real-time monitoring, clear insights, and peace of mind. Why does the SPN system matter? By distilling the complexities of a modern vehicle into a range of unique fault codes, SPNs allow technicians to quickly identify faults, allowing for rapid fixes that lower overall maintenance costs and reduce vehicle downtime. All this is achieved through: Diagnostic Precision — Because every SPN is tied to a specific function, once we read that number, we always know what the issue is, with no guesswork or further investigation needed. Fast Response — Because we know immediately what the issue is, we can then spend time fixing it, not finding it. Improved Safety — Faster fixes and earlier diagnosis means we get to issues before they become problems that impact vehicle safety. Keep Track in Real Time The AutoPi system is a solution that constantly monitors all vehicle systems for improved management of individual vehicles and the overall fleet. It works like this: Installation — Each truck in the fleet has a data logger fitted and connected directly to the CAN Bus, so it can communicate directly with the ECU. Monitoring — If you have an AutoPi device fitted to a vehicle, it monitors SPNs as they are generated from the vehicle’s ECU, such as SPN157, which relates to fuel pressure, or SPN 102, engine boost pressure. Alerts — If SPN 157 shows a fall in fuel pressure, a serious issue, then it can send you a warning via the AutoPi platform, so fleet managers are almost instantly aware of the problem. Preventative Action — In many cases, the alert can be dealt with by scheduling maintenance checkups when the vehicle returns. Maintenance Choices — However, the beauty of the system is it allows for informed choices. While something like 182, the boost pressure warning, can be looked at later, a fuel pressure problem should be dealt with immediately, because leaving it could cause further engine damage. In this example, the J1939 Parameter Group Number (PGN) 61444 relates to the Electronic Engine Controller 1. In this group there is a total of total of 8 SPNs, we can see all of these within a single CAN message, because it can use 8 distinct CAN signals as illustrated below. PGN 61444 Electronic Engine Controller 1 → CAN Message SPN 899 (Engine Torque Mode) → CAN signal #1 SPN 899 (Engine Torque Mode) → CAN signal #2 SPN 4154 (Actual Engine — Percent Torque) → CAN signal #3 SPN 512 (Driver's Demand Engine — Percent Torque) → CAN signal #4 SPN 513 (Actual Engine — Percent Torque) → CAN signal #5 SPN 190 (Engine Speed) → CAN signal #6 SPN 1483 (Source Address of Controlling Device for Engine Control) → CAN signal #7 SPN 1675 (Engine Starter Mode) → CAN signal #8 SPN 2432 (Engine Demand — Percent Torque) → CAN signal #9 We have made a guide on this, see how to decode SPN Messages with DBC File. Conclusion With modern vehicles so reliant on technology to function, we would need extensive time off the road to identify and rectify faults, or worse, not spot problems until it was too late, without the benefit of suspect parameter numbers. For anyone running a fleet of vehicles, the savings in time alone, never mind the increased safety, can be significant. By combining the benefits of SPNs with the real-time monitoring of AutoPi, fleet managers can see vehicle problems as they emerge, so we can always have fixes ready to go when a vehicle needs them. Questions? Let’s get in touch!
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