Connecting your laptop to your car’s Engine Control Unit (ECU) can unlock a wealth of diagnostic information, allowing you to understand your vehicle’s performance and identify potential issues. This guide focuses on connecting to older Subaru models, including those early OBD2 models that aren’t fully OBD2 compliant, often referred to as OBD1.5 or similar. We’ll walk you through the process step-by-step, focusing on using readily available tools to get you connected.
What You’ll Need to Get Started
To plug your laptop into your Subaru’s ECU, you’ll need a few key components. The most crucial piece of hardware is an FTDI TTL to USB lead. It’s important to select the 5-volt version to ensure compatibility with your Subaru’s system.
http://www.ftdichip.com/Products/EvaluationKits/TTL-232R.htm
Alt Text: Image of a FTDI TTL-232R USB to TTL Serial Cable, essential for connecting a laptop to a car ECU, highlighting its USB and TTL connector ends.
You can often find these leads from online retailers specializing in electronics components. For example, in regions like New Zealand and Australia, suppliers like Dontronics (http://www.dontronics-shop.com/ftdi-usb-to-serial-ttl-level-5v-converter-cable.html) are good sources.
http://www.dontronics-shop.com/ftdi-usb-to-serial-ttl-level-5v-converter-cable.html
For software, we’ll be using “ssm dump,” which is part of a software package available online. This tool is designed for Subaru diagnostics and will help us establish a connection and read data from your ECU. You can download this software from various Subaru enthusiast websites or forums. One example is vwrx.com, which hosts helpful resources and software for Subaru owners.
http://www.vwrx.com/index.php?pg=selectmonitor
Connecting Your Laptop to Your Subaru ECU: Step-by-Step
Once you have your FTDI cable and have downloaded the necessary software, follow these steps to connect your laptop to your car’s ECU.
Preparing the FTDI Cable
Start by preparing the FTDI cable for connection to your Subaru. You’ll need to strip the ends of three wires on the cable. These wires will correspond to specific pins in your Subaru’s diagnostic connector. Typically, the black wire is for ground, yellow is for the data transmit line, and orange is for the data receive line.
- Black Wire: Connects to ground (pin 9 on SSM connectors, or pin 4 or 5 on OBD2 connectors).
- Yellow Wire: Connects to the data transmit pin (pin 2 on SSM connectors, or pin 12 on OBD2 connectors).
- Orange Wire: Connects to the data receive pin (pin 3 on SSM connectors, or pin 13 on OBD2 connectors).
If you are working with an early OBD2 model Subaru, the pinout might be different from a fully compliant OBD2 system. Refer to resources like vwrx.com (http://www.vwrx.com/index.php?pg=selectmonitor) to confirm the correct pin locations for your specific vehicle and diagnostic plug type.
Connecting to Your Subaru’s Diagnostic Plug
Locate the diagnostic plug in your Subaru. Older models typically use the Subaru Select Monitor (SSM) connector, while slightly newer but still pre-OBD2 compliant models might have an OBD2 style connector that doesn’t fully adhere to the OBD2 standard.
For SSM connectors, you’ll be connecting the wires directly to the pins. For early OBD2 connectors, the pin assignments are as follows:
- Ground: Pin 4 or 5
- Transmit: Pin 12
- Receive: Pin 13
You can use a radio adapter plug from an auto-electrical shop for a cleaner connection to the SSM plug, but stripping the wires and stiffening the ends with solder also works effectively. The sockets in the car are designed to easily accept wire ends. Do not connect the cable to your car’s diagnostic port yet.
Installing FTDI Drivers
Before connecting the cable to your laptop, you need to install the necessary drivers for the FTDI chip. These drivers allow your computer to recognize the FTDI USB to serial adapter. Visit the FTDI website (http://www.ftdichip.com) and navigate to the driver download section. Follow the installation instructions provided on their site for your operating system.
Identifying the COM Port
Once the drivers are installed, plug the FTDI cable into your laptop. You need to determine which COM port has been assigned to the USB to serial adapter. On Windows, you can find this information in the Device Manager. Go to Control Panel -> System -> Hardware -> Device Manager, and look for “Ports (COM & LPT)”. Note down the COM port number assigned to the “USB Serial Port” or similar entry; you’ll need this for the diagnostic software.
Using SSM Dump to Test the Connection
Now, we will use the “ssm dump” software to test the connection. Extract the downloaded software package and locate the text configuration file (often named “ssm.txt” or similar). Open this file with a text editor. Find the line that specifies the COM port, usually “comport=2” by default. Change the number “2” to the COM port number you identified in the Device Manager. Save the configuration file.
Establishing Communication with the ECU
Now it’s time to connect the FTDI cable to your Subaru’s diagnostic port. Ensure the ignition is turned to the “ON” position (but do not start the engine). Run the “ssm dump” program.
- “47 48 49” Response: If you see “474849” displayed, it indicates that the request is being echoed back. This typically means there’s an issue with your COM port setting in the software configuration file. Double-check that you have entered the correct COM port number.
- “Null” Response: A “Null” response suggests no connection to the ECU. Check your wiring connections to the diagnostic plug, ensure the ignition is ON, and re-verify the COM port settings.
Identifying Your ECU and Data Logging
If the connection is successful, the “ssm dump” program will return an ECU identification number, which will look something like “7431XX”. This confirms that you have successfully plugged your laptop into your car ECU and established communication!
Once you have the ECU identification number, you can use the main “ssm” program to log data. Check the configuration files that come with the software for ECU definition files that match or are similar to your ECU number. If a matching definition file exists, you should be able to run the “ssm” program and start viewing live data from your Subaru’s ECU.
If your ECU number isn’t listed, you may need to identify a compatible definition file. The ECU number structure can provide clues:
- 1st Character: Often “7” for older models.
- 2nd Character: Year of ROM production (e.g., “0” for 1990, “4” for 1994).
- 3rd & 4th Characters: Car and engine type (e.g., “25” for SVX, “31/32/36/39” for Legacy, “3F/40” for Impreza).
- 5th Character: Market (e.g., “1” for JDM, “2” for USA, “3” for Europe).
- 6th Character: ROM revision.
You can experiment with definition files that are close to your ECU number, or try manually defining data addresses within the “ssm dump” tool to test specific parameters like battery voltage or engine RPM.
http://www.vwrx.com/index.php?pg=selectmonitor
Alt Text: Screenshot of a classic ECU diagnostic software interface, likely SSM, displaying real-time engine parameters and diagnostic data, emphasizing the visual output after connecting a laptop to a car ECU.
Conclusion: Unlock Your Subaru’s Data
Connecting your laptop to your Subaru ECU opens up a world of diagnostic and performance monitoring possibilities. By following these steps and using the right tools, you can gain valuable insights into your vehicle’s operation. While the “ssm” software is a great starting point, for more advanced features, faster data logging, and broader vehicle compatibility, consider exploring software like Evoscan (http://www.limitless.co.nz/). With a bit of patience and careful setup, you can effectively plug your laptop into your car ECU and start diagnosing like a pro.
