For owners of the 1994 Volvo 850, understanding how to diagnose issues can save time and money. While the 1994 model year predates the widespread adoption of OBD2 (On-Board Diagnostics II) systems, it still incorporates a diagnostic system that can be accessed without a standard OBD2 scan tool. This guide will walk you through the process of checking diagnostic codes on your 1994 Volvo 850.
Instead of the OBD2 port you might find in newer vehicles, the 1994 Volvo 850 utilizes a system with diagnostic boxes located under the hood. These boxes, labeled ‘A’ and ‘B’, are typically found on the front of the computer box in the engine compartment. Box ‘A’ is equipped with a wire, a plug, a button, and an LED light, which are key to retrieving fault codes.
Here’s how to read the codes using the LED method:
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Locate Diagnostic Boxes: Open your Volvo 850’s hood and find the computer box. Identify diagnostic boxes ‘A’ and ‘B’. Box ‘A’ will have the attached wire, button, and LED.
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Prepare for Code Reading: Turn the ignition key to the ‘ON’ position, but do not start the engine.
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Initiate Code Retrieval: Plug the wire from box ‘A’ into the designated hole for the system you want to check. For engine codes, use hole A2.
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Read the Blink Codes: Press the button on box ‘A’ for approximately one second and release. Observe the LED light. It will blink a series of times, pause, and then blink again in two more sets. These blinks represent a three-digit fault code. For example, blink-blink-blink, pause, blink-blink, blink would be code 3-2-1. A code of 1-1-1 indicates “no faults found.”
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Record and Interpret Codes: Write down each three-digit code as it is displayed. Be aware that multiple codes may be stored. After the first code is displayed, you’ll need to press the button again to check for additional codes. Repeat this process until all stored codes have been displayed.
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Clear the Codes (Optional): If you wish to clear the stored codes after diagnosing and addressing any issues, you can do so by pressing and holding the button on box ‘A’ for 5 to 10 seconds. Wait for the LED to light up, and then press and hold the button again for another 5 to 10 seconds.
For reference, you can find a list of potential fault codes and a visual guide to the diagnostic connectors and service light clearing method at VolvoSpeed Maintenance and VolvoSpeed Service Light Clearing.
While this method allows you to access basic diagnostic information without an OBD2 scanner on your 1994 Volvo 850, remember that for in-depth troubleshooting and corrective actions, consulting the factory service manuals is highly recommended. These manuals provide comprehensive procedures and are invaluable resources for maintaining your vehicle.
