Retro Diagnostics on a Classic BMW 8-Series
- Ryan Brown
- Jan 16, 2025
- 3 min read
Updated: Feb 1, 2025
Diagnostics has come a long way since the '90s, providing Topology Scans, Remote Assistance, Activation Tests and other valuable tools for repairing modern cars. However, for some jobs, older is just better.
Today at Rewired, we investigate an ABS light displayed on a 1990s 8-Series BMW using period-correct diagnostics equipment.
A Bit of History
CAN Bus is a communication medium designed by Bosch in the 1980s, aimed at reducing the vast amount of wire used within a road vehicle and to aid the various electronic modules to intercommunicate effectively. To say that it became a game changer, laying down the foundations of the electronic ecosystems we find in cars today, would be an understatement.
First introduced in the 1990s in the Mercedez-Benz W140 and the BMW 8 Series, the Controller Area Network protocol has since become an industry standard. With the addition of the On-Board Diagnostics interface, OBDII, mandated on all passenger vehicles since 1996, communicating with a vehicle to undertake repairs is a necessity growing more commonplace than ever.
However, there was a time before the common OBDII socket, that all new diagnostics tools use as standard, and today, we get to relive this era by diagnosing an ABS issue on this classic BMW.
The Tool Used
Being auto electrical specialists with a focus on classic cars, having the equipment to support older network interfaces is crucial. This is precisely why we still retain a working Launch GX3, a now considered "retro" or "vintage" diagnostic computer, amongst the others we have that are original to the period of the cars we repair.
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Plugging In
Along with old standards come old interfaces. Before the universally adopted OBDII, car manufacturers prided themselves on tools and sockets bespoke to proprietary interfaces. These sockets even changed on year ranges, requiring aftermarket diagnostic systems to supply a varied range of adapters to enable a user to plug in. For example, there are about 20 alternative adaptors included in this kit alone.
This year, BMW used a rounded socket placed by the battery jumping point at the bulkhead. Though there might be some chance of getting a newer tool to communicate if using a compatible adapter, a tool like this, at the cutting edge of this period, has decided features that a modern tool would overlook, especially when it comes to reading faults outside of the scope of general engine errors.
Removing this cover exposes a circular set of pins, for which our launch has an adapter we can use to plug in.
After selecting the manufacturer, year, and model of the vehicle on the tools screen, we can begin to read the codes stored in the vehicle's Detected Trouble Code memory.
Reading Codes
The code stored within the ABS control module was that of detected fault internal to the pump unit itself - a common issue with this age of car.
Solving the Issue
After playing a little game of hide and seek, we found the module sneakily tucked away under the headlight.
Fortunately, a good-condition second-hand pump was sourced. Before removing the old pump, we plugged in the new unit electrically and found that the code was now able to be cleared. Along with other checks (testing fuses, looking for damage on connectors and wires), this test allowed us to further verify that the issue was internal to the pump before committing to the mechanical overhead of removing the old unit and disconnecting and bleeding brake lines. Now the issue has gone, the new part can be properly fitted and further tested.
Once the unit was fitted, the brake system was bled and further tested with a test drive. The issue did not return, whereas before, the light would come back straight away after clearing the code from memory.
Once again, an old tool comes to rescue another classic car.
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