The Volvo 940, a classic known for its robustness and reliability, often presents a unique challenge to modern car enthusiasts and DIY mechanics, especially when it comes to diagnostics. If you’re the proud owner of a 1997 or similar vintage 940 HPT and have encountered an OBDII port in your center console, you might have been misled into thinking that generic OBDII code readers would seamlessly plug in and reveal your car’s secrets. However, as many Volvo owners have discovered, the relationship with your 940’s OBDII port is a bit more nuanced – think of it as the automotive equivalent of the Kama Sutra, requiring a specific approach to unlock its hidden knowledge.
This guide, inspired by the resourceful discussions in the Volvo Owners Club Forum, delves into the intricacies of reading fault codes on your 1997 Volvo 940 HPT. We’ll explore why standard OBDII readers often fail and, more importantly, how to take matters into your own hands with a DIY LED code reader, ensuring you can effectively diagnose and maintain your beloved Volvo.
The OBDII Illusion: Why Generic Readers Fall Short
The presence of a 16-pin OBDII socket in your 1997 Volvo 940 HPT can be deceiving. While it physically resembles the standardized OBDII ports found in modern vehicles, the 940’s system is not fully OBDII compliant. This crucial detail is often the source of frustration for owners who find their off-the-shelf OBDII readers unable to communicate with the car’s Engine Control Unit (ECU).
As forum user p.j. initially discovered, plugging in a Gendan p.c. based reader resulted in a communication failure. This experience is common, highlighting a critical point: generic OBDII scanners are not designed to interpret the specific communication protocols used by Volvo in this era. The 940’s system, while incorporating the OBDII port, operates on a Volvo-specific diagnostic language.
Understanding the OBDII Port: While physically present in the Volvo 940, this port does not adhere to the fully standardized OBDII protocols, necessitating alternative diagnostic approaches.
This isn’t to say the OBDII port is entirely useless. It’s the gateway to your car’s diagnostic system, but it requires a translator – a tool capable of speaking Volvo’s language. This is where the ingenuity of the Volvo community shines, offering a cost-effective and empowering solution: the DIY LED code reader.
Embracing the DIY Diagnostic Path: The LED Code Reader
Faced with the limitations of generic OBDII tools and the prohibitive cost of Volvo’s proprietary VT2000 diagnostic box (mentioned to be around £1000 by forum user CTCNetwork), the DIY approach emerges as the most practical and accessible route for most Volvo 940 owners. Inspired by the resourcefulness shared on the Volvo forums, building your own LED code reader is not only feasible but also a rewarding endeavor for any car enthusiast.
The concept is elegantly simple: create a circuit with an LED that flashes in patterns to represent fault codes. This method taps directly into the diagnostic pins of the OBDII port, bypassing the need for complex communication protocols that generic readers struggle with. Forum user CTCNetwork pointed to a helpful thread detailing the construction of a “Diagnostic Test Box,” and gpl1968 further expanded on this by building a reader capable of accessing ABS (pin 12) and Cruise Control (pin 13) codes in addition to the standard engine codes.
Schematic Diagram of DIY Code Reader: This diagram, shared by forum user gpl1968, illustrates the simplicity of building a custom LED code reader for Volvo 940 diagnostics, utilizing readily available electronic components.
Building Your Own Volvo Code Reader: A Practical Guide
Based on the shared experiences and diagrams within the Volvo forum, constructing your own code reader is a straightforward project. You’ll need basic electronic components and some minimal soldering skills. Here’s a simplified approach based on the information provided:
Components You’ll Need:
- LED (Light Emitting Diode)
- Resistor (appropriate value for the LED and 12V circuit – check online calculators for LED resistor values)
- Push Button Switch (momentary)
- Wiring
- OBDII connector or pins (to connect to your car’s OBDII port – you can salvage these or buy them online)
- Project Box (optional, to house the components neatly)
Basic Circuit:
- Power: The reader is powered by the car’s 12V system, drawing power from the OBDII port itself (pin 16 is typically +12V, pin 4 or 5 is ground).
- Selection Pins: A selector switch (or individual connections) is used to choose which system to read codes from. Common pins for Volvo 940 diagnostics include:
- Pin 1: Ignition System (EZK)
- Pin 3: Fuel Injection System (ECU/LH-Jetronic)
- Pin 12: ABS (Anti-lock Braking System)
- Pin 13: Cruise Control
- (Note: Pin 7 for SRS mentioned in the forum may require Volvo specific tools and might not be accessible with this DIY reader, as noted by gpl1968)
- LED and Resistor: Connect the LED and resistor in series. This combination is connected between the selected diagnostic pin and ground.
- Push Button: The push button is used to initiate the code reading process. It typically connects to the diagnostic pin, momentarily grounding it to trigger the code output.
Assembly:
- Solder the components together according to the schematic. The diagram from gpl1968 provides a clear visual guide.
- If using a project box, mount the LED and button on the box for easy access.
- Connect wires to the OBDII connector pins, ensuring correct pin assignments based on OBDII port diagrams (easily found online).
Using Your DIY Code Reader:
- Ignition ON: Turn the ignition key to the “ON” position (position 2) but do not start the engine.
- Select System: Choose the system you want to diagnose (e.g., ECU, EZK, ABS) using your selector switch or by connecting to the appropriate pin.
- Initiate Code Reading: Press and hold the push button for a few seconds (forum users suggest around 2 seconds, but consult Volvo documentation if available for precise timing). Release the button.
- Count the Flashes: The LED will now blink a series of pulses. Volvo fault codes are typically two or three-digit numbers, represented by flashes.
- Example: Flashes might be in a pattern like: “Flash, Flash, Flash — Flash, Flash — Flash, Flash, Flash” This would be interpreted as code 323. Longer pauses separate digits, shorter pauses separate codes.
- Consult Code List: Refer to a Volvo 940 fault code list (readily available online – the Volvo Club UK FAQ mentioned by forum users is a good resource). Match the LED flash patterns to the corresponding fault codes to understand the issue.
Example of a Homemade Code Reader: As showcased by gpl1968, a DIY code reader for Volvo 940s can be compact and functional, providing a practical solution for accessing diagnostic information.
Decoding the Diagnostic Kama Sutra: Patience and Practice
Like mastering any intricate art, effectively using your DIY code reader requires a bit of patience and practice. The flash patterns can sometimes be a little tricky to interpret initially. It’s recommended to practice reading codes even when you don’t suspect any faults to become familiar with the process and the expected “no fault” code (often 1-1-1 or similar, depending on the system).
Forum user rogerthechorister, in a moment of diagnostic frustration, humorously described the insertion of the code reader pins as reaching “Kama Sutra standard,” highlighting the sometimes delicate and precise nature of ensuring good connections. Wiggling the connections slightly, as suggested by barkster1971, can sometimes be necessary to establish proper contact and get reliable readings.
Beyond Basic Codes: ABS, SRS, and the Limits of DIY
While the DIY LED reader is excellent for accessing engine and related system codes, the forum discussion touches upon the complexities of other systems like ABS and SRS. gpl1968 successfully incorporated ABS and Cruise Control code reading into their DIY reader, demonstrating its expanded capabilities. However, accessing SRS (Airbag) codes might be more challenging.
As Tiziano958 discovered, pin 7, often associated with SRS, might not respond to the DIY reader. gpl1968 suggested that SRS diagnostics might require Volvo’s proprietary VCT2000 tool or a visit to a Volvo dealer. However, forum user kamyk1313 mentioned “Vol-FCR” software and a “VAG cable” as a potential method for reading SRS data, suggesting that there might be software-based solutions beyond the simple LED reader, although potentially requiring more technical expertise.
For ABS issues, barkster1971 mentioned success with a generic OBDII tool specifically for ABS, indicating that while full OBDII compliance is lacking, some systems might be partially accessible through more specialized generic scanners.
Community Wisdom: The Strength of Shared Knowledge
The Volvo Owners Club Forum thread is a testament to the power of community-driven problem-solving. From the initial question about OBDII reader compatibility to the detailed diagrams and troubleshooting advice, the forum provides invaluable support for Volvo 940 owners. The willingness of users like gpl1968, CTCNetwork, oakey, and many others to share their experiences and solutions embodies the spirit of DIY car maintenance and the strength of online communities.
The journey of diagnosing your Volvo 940’s fault codes might not be as straightforward as plugging in a generic OBDII scanner. But with the knowledge and resourcefulness shared within the Volvo community, and by embracing the “diagnostic Kama Sutra” – the art of intricate and hands-on problem-solving – you can effectively communicate with your car, understand its needs, and keep it running smoothly for years to come. Building your own LED code reader is not just a practical solution; it’s a rewarding step in deepening your understanding of your classic Volvo and joining a community of passionate owners.
