The Volvo 850, a vehicle celebrated for its durability and distinctive design, often presents a unique scenario for car owners when it comes to diagnostics. If you own an early Volvo 850 and are trying to use a standard OBD2 scanner, you might be encountering some confusion. The question of Obd2 Volvo 850 compatibility is a common one, and understanding the nuances can save you time and frustration. This article will clarify the situation, explain how to diagnose your early 850, and ensure you get the insights you need into your car’s health.
Understanding the OBD2 Port on Early Volvo 850s: It’s Complicated
You’ll find an OBD2 port in your early Volvo 850, typically located under the dashboard. This might lead you to believe that your vehicle is fully OBD2 compliant, ready to communicate with any standard OBD2 scanner. However, for many early 850 models, particularly those manufactured before 1996, this isn’t entirely the case.
While Volvo equipped these models with the physical OBD2 connector, the underlying communication protocols weren’t fully aligned with the standardized OBD2 we know today. This was a period of transition in the automotive industry, with manufacturers adopting OBD2 at different paces. Think of it as a precursor to the fully standardized systems. The presence of the OBD2 port was partly driven by emerging regulations, especially in the US market, but the implementation was, in many respects, Volvo’s proprietary system wired to an OBD2 socket.
This means that while the port looks like an OBD2 port, and in some limited ways acts like one (like resetting the service light), it won’t provide comprehensive diagnostic data when connected to a generic OBD2 scanner. Attempting to use a standard scanner might result in communication errors or a failure to retrieve fault codes.
Reading Fault Codes on Early Volvo 850s: The Flash Code Method
So, if standard OBD2 scanners aren’t fully effective, how do you diagnose an early obd2 volvo 850? The answer lies in understanding the flash code system. These early systems used a method of flashing an LED to communicate diagnostic trouble codes (DTCs). This might sound rudimentary compared to modern digital scanners, but it’s a reliable way to access information from your 850’s various control modules.
The forum discussions reveal a clever DIY approach using a simple circuit: an LED, a resistor, and a switch. Here’s a breakdown of how this works based on the information shared:
To retrieve flash codes, you need to construct a simple circuit. You will need:
- An LED (Light Emitting Diode)
- A 1.8 kΩ (1800 ohm) resistor
- A push-to-make switch
- Connecting wires
Connect the components as follows:
- Connect the LED and resistor in series (positive leg of LED to the resistor).
- Connect one end of this LED-resistor combination to pin 16 (+) of the OBD2 connector (this is the +12V power supply).
- Connect the other end of the LED-resistor combination to the pin corresponding to the module you want to read (Pin X in the forum discussion). See the pin assignments below.
- Connect one side of the push-to-make switch to the same Pin X.
- Connect the other side of the switch to pin 4 or 5 (-) of the OBD2 connector (ground).
Here’s a table summarizing the pin assignments for different modules, as discussed in the forum:
| Module | Pin (X) | ECU/System |
|---|---|---|
| Engine ECU | 3 | Motronic 4.3 or Fenix 5.2 |
| ECC (Electronic Climate Control) | 6 | 850 ECC |
| Timer Type 4 | 9 | Additional Heater (less common) |
| Cruise Control | 13 | All models |
| ABS (Anti-lock Braking System) | 12 | 900 & S/V 90 ABS (Potentially for some 850 ABS, verify) |
Important Note: The ABS pin (12) mentioned is noted for 900 & S/V 90 ABS, and it’s suggested to verify its applicability for your specific 850 ABS system. Further investigation might be needed to confirm if pin 12 is indeed the correct pin for ABS on all early 850s. The later discussion in the forum suggests pin 12 might not be for ABS on all 850 variants.
How to Read Flash Codes:
- Connect your DIY tool to the OBD2 port.
- Turn the ignition to the “ON” position (do not start the engine).
- Press and hold the push-to-make switch for 1-3 seconds, then release.
- Observe the LED flashes. The codes are typically two-digit or three-digit codes, indicated by a series of flashes. For example, code 1-2-2 would be one flash, a short pause, two flashes, another short pause, and then two flashes again. Longer pauses separate different codes if multiple codes are stored.
- Consult a Volvo 850 repair manual or online resources to decode these flash codes. The forum mentions Haynes manuals as a potential source for code look-up.
The forum users noted that the LED flashes can be “painfully slow,” so be patient when reading the codes.
OBD2 Compliance: The Later 20V Model and Beyond
It’s crucial to highlight that not all Volvo 850s are created equal when it comes to OBD2. The forum clearly states that the only 850 engine that’s truly OBD2 compliant in Europe is the late 20V model equipped with Motronic 4.4 engine management. If you own this specific variant of the 850, you might have better luck with standard OBD2 scanners for engine diagnostics.
Furthermore, the discussion extends to later models, noting that:
- Volvo S/V70 models with Motronic 4.4 or the later ME7 engine management systems are OBD2 compliant.
- Volvo S/V70 10V cars with Fenix 5.2 are not fully OBD2 compliant and may require the flash code method, similar to early 850s, or specialized tools.
This distinction is vital for anyone working on Volvo diagnostics. Knowing your engine type and model year is key to choosing the right diagnostic approach.
Using OBD2 Scanners and Specialized Tools
Given the complexities, what are your options for diagnosing a obd2 volvo 850?
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For Early 850s (Pre-OBD2 Compliant Models):
- DIY Flash Code Tool: As described above, this is a low-cost and effective method for reading basic fault codes from various modules.
- Volvo Specific Scan Tools: Professional-grade or Volvo-specific scan tools designed for older models can communicate with these systems. The forum mentions “Alex Peper interface cable” and software that can access ABS, SRS, and other modules on these earlier cars. These tools often go beyond basic OBD2 functionalities and can offer more in-depth diagnostics and module communication.
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For Later 850 20V (Motronic 4.4) and OBD2 Compliant Models:
- Standard OBD2 Scanners: For engine-related codes on these models, a standard OBD2 scanner should work. However, for deeper diagnostics and access to other modules (ABS, SRS, etc.), a more advanced scan tool might still be beneficial.
- Volvo Specific Scan Tools: Even for OBD2 compliant Volvo 850s and subsequent models, Volvo-specific tools offer the most comprehensive diagnostic capabilities, including access to all modules, advanced functions, and manufacturer-specific codes that generic OBD2 scanners might miss.
Troubleshooting and Common Issues
The forum thread also touches on a common issue in Volvo 850 ABS systems: ABS cable problems due to crimped wires under the fuse box. This is a valuable insight for 850 owners experiencing ABS faults. The discussion suggests that these crimps can degrade, leading to signal issues, particularly at low speeds, causing the ABS to engage prematurely.
Solutions mentioned include:
- Re-crimping the Wires: Locating and re-crimping the faulty connections under the fuse box. This is a more involved DIY repair.
- Volvo Extended Cable Kit: Volvo offered a repair kit with extended cables to bypass the problematic crimped sections.
Another point raised is the importance of sensor cleaning for ABS. Sensors caked in debris can cause inaccurate readings. Also, incorrect tire pressure is mentioned as a potential factor, although this is less directly related to OBD2 diagnostics.
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Example of ABS fault codes retrieved using diagnostic software on a Volvo 850.
Conclusion: Navigating OBD2 on Your Volvo 850
Diagnosing a obd2 volvo 850 requires understanding the specific model year and engine management system. Early Volvo 850s, while equipped with an OBD2 style port, are not fully OBD2 compliant and often require the flash code method or Volvo-specific diagnostic tools. Later 850 20V models with Motronic 4.4 are OBD2 compliant for engine codes, but comprehensive diagnostics may still benefit from specialized tools.
For owners of early 850s, the DIY LED flash code tool is a valuable and accessible method for retrieving fault information. For more in-depth diagnostics, especially on ABS, SRS, and other systems, consider seeking out Volvo-specific scan tools or professional diagnostic services. By understanding these nuances, you can effectively troubleshoot your Volvo 850 and keep this classic car running smoothly.
