Engine speed is one of the most frequently monitored parameters in any SAE J1939 network. Whether you are developing a dashboard, testing an engine ECU, validating telematics software, or learning how J1939 communication works, engine speed is often the first parameter engineers look at.
In this post, we will explain how to simulate engine speed using our JCOM1939 Monitor software. We will begin with a brief overview of the SAE J1939 message that carries engine speed information and then demonstrate how to configure and transmit the message on a J1939 network.
PGN 61444 – Electronic Engine Controller 1 (EEC1)
In the SAE J1939 protocol, engine speed is transmitted through PGN 61444, also known as Electronic Engine Controller 1 (EEC1). This message is typically broadcast by the engine ECU at a rate of 10 messages per second (every 100 milliseconds) and contains several engine-related parameters in addition to engine speed.
The following table summarizes the contents of PGN 61444.
| Byte(s) | SPN | Parameter |
|---|---|---|
| 1 (bits 1-4) | 899 | Engine Torque Mode |
| 1 (bits 5-8) | 4154 | Actual Engine Percent Torque (Fractional) |
| 2 | 512 | Driver’s Demand Engine Percent Torque |
| 3 | 513 | Actual Engine Percent Torque |
| 4-5 | 190 | Engine Speed |
| 6 | 1483 | Source Address of Controlling Device |
| 7 (bits 1-4) | 1675 | Engine Starter Mode |
| 7 (bits 5-8) | Reserved | |
| 8 | Reserved |
SPN 899 – Engine Torque Mode
This parameter indicates how the engine torque is currently being controlled. Depending on the operating conditions, the torque may be governed by the accelerator pedal, cruise control, PTO operation, idle governor, or other control functions.
The value is transmitted as an enumeration and provides insight into the current operating mode of the engine controller.
SPN 4154 – Actual Engine Percent Torque Fractional
This parameter provides additional resolution for the actual engine torque value reported in SPN 513.
By combining SPN 513 and SPN 4154, applications can display engine torque with a finer level of precision than would be possible using the integer torque value alone.
SPN 512 – Driver’s Demand Engine Percent Torque
This parameter represents the torque requested by the driver through the accelerator pedal.
The value is encoded with an offset of -125 percent:
Driver’s Demand Torque (%) = Raw Value – 125
For example, a raw value of 175 corresponds to a requested torque of 50%.
SPN 513 – Actual Engine Percent Torque
This parameter represents the actual torque currently being delivered by the engine relative to its rated torque.
Like SPN 512, the value is encoded with an offset of -125 percent:
Actual Torque (%) = Raw Value – 125
Comparing the driver’s demand torque with the actual torque can provide valuable insight into engine load conditions and engine control behavior.
SPN 190 – Engine Speed
SPN 190 is by far the most widely used parameter in PGN 61444.
Engine speed is transmitted as a 16-bit value located in bytes 4 and 5 using Intel (little-endian) byte order.
The conversion formula is:
Engine Speed (rpm) = Raw Value × 0.125
For example:
Raw Value = 8000
Engine Speed = 8000 × 0.125 = 1000 rpm
Because engine speed is required by many vehicle subsystems, PGN 61444 is normally transmitted continuously by the engine ECU throughout vehicle operation.
SPN 1483 – Source Address of Controlling Device
This parameter identifies the J1939 source address of the controller currently exercising authority over engine operation.
In most applications, this will be the engine ECU itself. However, in systems using cruise control, PTO control, or remote throttle control, another ECU may temporarily assume control.
SPN 1675 – Engine Starter Mode
This parameter reports the status of the engine starting system.
Typical states include starter inactive, starter engaged, start request received, start completed, and various inhibit conditions.
Monitoring this parameter can be useful during diagnostics and troubleshooting of engine starting issues.
Engine Speed Simulation
As mentioned previously, we will use the JCOM1939 Monitor software, connected to the J1939 network through the JCOM.J1939.USB gateway, to configure and transmit engine speed data.
In the Transmit section, we enter PGN 61444, assign a priority of 3, and set the transmission interval to 100 milliseconds, which matches the typical transmission rate of the EEC1 message. Next, we enter the message data—arbitrary values in this example—along with a descriptive label for the message.
After clicking the Save button, the newly configured PGN will appear in the transmit data view below, where it is available for transmission and further editing.
At this point, no data is being transmitted because the gateway has not yet claimed a J1939 node address. A valid source address is mandatory before any J1939 messages can be transmitted on the network.
To claim an address, switch to the ECU Setup section, select ECU SImulation Mode and claim Address 128. While you may choose any valid J1939 source address, we will use the default value of 128 for this example.
After clicking the Claim Address button, the gateway initiates the J1939 Address Claim procedure. Once the address has been successfully claimed, the gateway immediately begins transmitting the configured EEC1 message, as shown in the image below.
Please note that a J1939 network requires at least two connected nodes to operate correctly. Therefore, in addition to the JCOM.J1939.USB gateway, you will need a second J1939-compatible device connected to the network to establish proper bus communication.
Now you may ask: How do we modify the engine speed?
One option would be to return to the Transmit section, select PGN 61444 from the list, modify the data bytes manually, and click the Save button again. While this approach works, there is a much more convenient method.
Switch to the Byte Data section and select PGN 61444 from the list box. According to the SAE J1939 standard, engine speed (SPN 190) is located in bytes 4 and 5 of the EEC1 message and occupies two bytes, as shown in the setup below.
Once the byte data configuration has been completed, the slider and data field are automatically synchronized with the current engine speed value contained in the message. You can then use the slider to increase or decrease the engine speed in real time. Alternatively, you can enter a specific value directly into the data field for precise control.
As the value changes, the software automatically updates the corresponding data bytes in PGN 61444 and continues transmitting the modified message at the configured interval. This makes it easy to simulate changing engine operating conditions without manually editing the raw message data.
Conclusion
Simulating engine speed on a J1939 network is straightforward with the JCOM1939 Monitor software and the JCOM.J1939.USB gateway. By configuring and transmitting PGN 61444 (EEC1), you can quickly create a realistic engine speed source for testing dashboards, data loggers, telematics devices, ECUs, and other J1939-compatible equipment.
The Byte Data feature further simplifies the process by allowing you to adjust engine speed interactively while the message is being transmitted. This eliminates the need to repeatedly edit raw data bytes and provides a convenient way to simulate dynamic engine behavior during development, testing, and troubleshooting.
SAE J1939 Starter Kit and Network Simulator
Our JCOM.J1939 Starter Kit and Network Simulator is designed to allow the experienced engineer and the beginner to experiment with SAE J1939 data communication without the need to connect to a real-world J1939 network, i.e., a diesel engine. It may sound obvious, but you need at least two nodes to establish a network. That fact applies especially to CAN/J1939, where the CAN controller shuts down after transmitting data without receiving a response. Therefore, our jCOM.J1939 Starter Kit and Network Simulator consists of two J1939 nodes, namely our jCOM.J1939.USB, an SAE J1939 ECU Simulator Board with USB Port.
The jCOM.J1939.USB gateway board is a high-performance, low-latency vehicle network adapter for SAE J1939 applications. The board supports the full SAE J1939 protocol according to J1939/81 Network Management (Address Claiming) and J1939/21 Transport Protocol (TP). More Information…
Comments are closed.