Navigating vehicle diagnostics can feel like deciphering a secret language, especially when dealing with older models. If you’re tackling issues with your 1995 Old Body Style (OBS) diesel truck and searching for an OBD2 port to check the codes, you’ve come to the right place. While the term “OBD2” might be slightly misleading for this classic year, understanding the diagnostic system it does have is straightforward. Let’s dive into how you can check the trouble codes on your 1995 OBS diesel.
For 1995 OBS trucks, including diesel models, the diagnostic system is OBD-I, not OBD2. This system, while less advanced than OBD2, still provides valuable information about your engine’s health through trouble codes. Instead of an OBD2 port, you’ll be looking for the Data Link Connector (DLC), also sometimes referred to as the Assembly Line Diagnostic Link (ALDL). This connector is typically located under the driver’s side dashboard.
To access the diagnostic information, you won’t need any fancy scan tools. All you need is a simple paper clip or a small piece of wire to “jump” two specific terminals within the DLC. Here’s how to do it:
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Locate the DLC: Get down to the driver’s side footwell and look under the dash. You’re searching for the DLC connector.
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Identify Terminals A and B: The DLC connector has multiple terminals. You need to locate terminals A and B. In most cases, terminal A is on the top right, and terminal B is directly next to it to the left. The image below illustrates the location of terminals A and B on a typical DLC connector.
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Jumper Terminals A and B: With the ignition switch turned off, use your paper clip or wire to create a connection between terminal A and terminal B. Insert one end of the paper clip into terminal A and the other into terminal B.
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Turn the Ignition On (Do Not Start the Engine): Turn the ignition key to the “ON” position, but do not start the engine.
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Observe the “Service Engine Soon” Light: Watch the “Service Engine Soon” light (sometimes labeled “Check Engine”) on your dashboard. It will begin to flash a sequence of codes.
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Interpreting the Codes: The codes are communicated through flashes of the “Service Engine Soon” light. A code is represented by a series of flashes, a pause, and then another series of flashes.
- Code 12 is the starting point and a system pass code. It’s indicated by one flash, a pause, and then two flashes (flash, pause, flash flash). Code 12 will typically flash three times at the beginning.
- Subsequent codes will also flash three times each before moving to the next code in numerical order.
- The sequence repeats once all stored codes have been displayed, starting again with code 12.
Example: If you see the sequence: flash, pause, flash flash (repeated three times), then flash flash, pause, flash flash flash flash (repeated three times), your codes are 12 and 24.
Understanding the Codes and Next Steps:
It’s crucial to remember that a trouble code is just a starting point for diagnosis. It indicates a potential issue within a system but doesn’t pinpoint the exact faulty component. For example, a code related to the oxygen sensor might not mean the sensor itself is bad; it could be reporting an issue elsewhere in the system affecting its readings.
Basic Gasoline Engine OBD-I Codes (Note: Diesel codes are different and more extensive):
While the original list provided was for gasoline engines, it gives you an idea of the type of codes OBD-I systems report. Diesel-specific OBD-I codes for your 1995 OBS diesel will be different and more relevant to diesel engine systems. For accurate diesel codes, you’ll need to consult a diesel-specific OBD-I code list for your truck’s year and engine.
Here are a few examples from the original gasoline list to illustrate code types:
- 13 – O2 (oxygen sensor) circuit open
- 14 – ECT/CTS (engine coolant temperature) sensor circuit low (high temperature)
- 21 – TPS (throttle position sensor) circuit high (signal voltage high)
- 33 – MAP (manifold absolute pressure) sensor circuit high (low vacuum)
Clearing Codes:
You can clear the stored codes by disconnecting the negative battery terminal for about 20 seconds. Codes will also automatically clear after approximately 50 engine starts if the fault condition is no longer present.
Moving Forward:
Once you’ve retrieved the codes from your 1995 OBS diesel, your next step is to find a diesel-specific OBD-I code list for your truck. This list will provide the descriptions relevant to your diesel engine. Remember to use the codes as a guide for further investigation and troubleshooting. If you’re unsure about interpreting the codes or diagnosing the problem, it’s always best to consult a qualified mechanic experienced with older diesel vehicles. They can accurately diagnose the root cause and perform the necessary repairs to get your OBS diesel running smoothly.
