So, you’ve joined the growing ranks of enthusiasts enjoying the unique performance of a ’99 Subaru Legacy GT, especially those cool twin-turbo models hitting US shores after turning 25 years old. Welcome to the club! One of the first things you might need to do when owning a slightly older vehicle is to run a diagnostic check, and that starts with finding your OBD2 port. But beyond just locating the port, understanding how to use it is key to keeping your Legacy GT running smoothly, especially when dealing with the intricacies of its twin-turbo system.
Locating the OBD2 Port in Your ’99 Subaru Legacy GT
First things first, let’s pinpoint the OBD2 port location in your 1999 Subaru Legacy GT. Thankfully, it’s in a pretty standard spot for vehicles of this era, making it easy to access.
You’ll want to look under the driver’s side dashboard. Get down near the pedals and peer upwards and towards the center of the car. The OBD2 port is typically located on the lower edge of the dashboard, often near the steering column. It’s usually a black, trapezoid-shaped connector with 16 pins inside.
An example image showing a general area where OBD2 ports are typically located in cars. While not a ’99 Legacy GT specifically, it gives a good indication of where to look.
Once you’ve located the port, you’re ready to connect an OBD2 scanner. This is your first step in understanding the health of your engine and diagnosing any potential issues, including those specific to the twin-turbo system.
Diving Deeper: Using OBD2 for Twin Turbo Diagnostics
While finding the OBD2 port is simple, understanding what it can tell you about your twin-turbo Legacy GT is where things get interesting. These JDM (Japanese Domestic Market) models, especially the twin-turbo variants, have a reputation for their complex vacuum systems and unique engine management. The OBD2 port is your window into this system, allowing you to read trouble codes and get a sense of what might be going on under the hood.
Common Trouble Codes and Code 66
One code you might encounter, especially with twin-turbo Legacys, is the infamous Code 66. As mentioned in forums dedicated to these cars, Code 66 isn’t your typical OBD2 code that points to a specific sensor. Instead, it’s a general “twin turbocharger system” error, indicating that the ECU (Engine Control Unit) has detected a problem with the boost performance.
A glimpse into the engine bay, highlighting the complex vacuum lines often associated with Subaru’s twin-turbo systems. Understanding these lines is crucial for diagnosing issues related to Code 66.
Code 66 can be triggered by a variety of issues, including:
- Vacuum Leaks: A cracked or disconnected vacuum line is a prime suspect. Given the age of these cars, rubber components can degrade, leading to leaks that disrupt the delicate balance of the twin-turbo system.
- Incorrect Vacuum Line Routing: If previous maintenance was performed, there’s a chance vacuum lines were reconnected incorrectly. Different Legacy GT models and engine revisions have varying vacuum layouts, so using the wrong diagram can cause problems.
- Turbocharger Issues: While less common than vacuum leaks, a failing primary turbo can also lead to Code 66.
When you get a Code 66, you’ll likely notice a significant drop in performance, often described as a “hard cut” in power. Using your OBD2 scanner to read this code is just the first step. You’ll then need to investigate further to pinpoint the root cause.
Reading Error Codes on Your ’99 Legacy GT
To read error codes using the OBD2 port on your ’99 Legacy GT, you’ll need an OBD2 scanner. These scanners are readily available online and at auto parts stores. Once you have a scanner:
- Locate the OBD2 port as described earlier.
- Turn the ignition to the “ON” position (without starting the engine).
- Plug the OBD2 scanner into the port.
- Follow the scanner’s instructions to read trouble codes. The scanner will communicate with the car’s ECU and display any stored codes.
A visual representation of connecting an OBD2 scanner to the port. This is the first step in retrieving valuable diagnostic information from your ’99 Subaru Legacy GT.
Make note of any codes displayed. While generic OBD2 scanners can read basic engine codes, for deeper diagnostics, especially related to the twin-turbo system, you might consider a Subaru-specific scanner or software.
Beyond OBD2: Manual Code Reading (For Older Systems)
Interestingly, the original article mentions an older, OBD-I style method for reading codes on these JDM Subarus, which might still be relevant or offer additional information alongside OBD2. This involves using “Dealer Check Connectors” (green) and “Read Connectors” (black) typically found under the dash.
An example of the diagnostic connectors mentioned for older Subaru models. While OBD2 is the primary interface, understanding these legacy connectors can be helpful for comprehensive diagnostics.
While OBD2 is the standard interface, being aware of these older diagnostic connectors highlights the blend of older and newer technologies in these ’99 Legacy GTs. The OBD2 port provides modern scanner compatibility, while the legacy connectors reflect the car’s earlier engineering roots.
Troubleshooting Tips for Code 66 and Twin Turbo Issues
Once you’ve read your codes, especially if you encounter Code 66, here’s a breakdown of troubleshooting steps, drawing from expert knowledge and common issues:
-
Visual Inspection of Vacuum Lines: Carefully examine all vacuum lines in the engine bay. Look for cracks, disconnections, or signs of wear. Pay close attention to the lines connected to the “Black Box of Death” (BBoD), which is central to the twin-turbo control.
A detailed view of engine bay components and vacuum lines. Thoroughly inspecting these lines is crucial for diagnosing boost and performance issues in twin-turbo Subaru Legacy GTs.
-
Verify Vacuum Line Routing: If you suspect incorrect routing, find a reliable vacuum diagram specific to your ’99 Legacy GT model and engine revision. These diagrams can be found in online forums and service manuals (links to resources are often invaluable).
-
Check for Boost Leaks: Inspect intercooler hoses and connections for leaks. Listen for hissing sounds while the engine is running, which can indicate a boost leak.
-
Inspect Intake Pipes: Check for cracks or leaks in the intake pipes, especially around the PCV valve connection and turbo inlets.
-
Consider MAF Sensor: A faulty MAF (Mass Air Flow) sensor can sometimes trigger Code 66. While less common, it’s worth considering, especially if other checks don’t reveal the problem.
-
Spark Plugs and Coil Packs: In rare cases, misfires due to worn spark plugs or faulty coil packs can contribute to performance issues that trigger Code 66.
-
Turbocharger Health: If all else fails, consider the possibility of a failing primary turbo. Listen for unusual noises from the turbocharger and check for excessive oil smoke.
Conclusion: OBD2 Port – Your Starting Point for Legacy GT Maintenance
Finding the OBD2 port on your ’99 Subaru Legacy GT is the first step in taking control of its maintenance and understanding its unique twin-turbo system. By using an OBD2 scanner and understanding common codes like Code 66, you can begin to diagnose and address potential issues. Combined with visual inspections and expert knowledge, the OBD2 port becomes a valuable tool in keeping your JDM gem running at its best, allowing you to fully enjoy the thrill of its distinctive twin-turbo performance. Remember to consult resources and diagrams specific to your model year and engine revision for the most accurate troubleshooting.
