Upgrading your classic E30 BMW with a more modern M52 or S52 engine brings a significant boost in performance. However, integrating the OBD2 system from these engines into the older E30 chassis requires some wiring know-how, particularly when it comes to Obd2 Wiring. This guide provides a clear walkthrough on how to wire a glovebox OBD2 port for your E30 with an M52/S52 harness, making diagnostics and ECU flashing more accessible.
Wiring Your OBD2 Port: Step-by-Step
This guide references specific BMW Electrical Troubleshooting Manual (ETM) page numbers and connector designations for clarity. For reference, X19527 is the E36 OBD2 port connector, X6000 is the DME (Digital Motor Electronics) connector, X6002 is the underhood 20-pin ADS connector, and X6031 is the smaller connector found on a stock OBD2 M52/S52 harness, near connectors X20 and X69.
Understanding the OBD2 Pinout
Let’s break down the essential OBD2 wiring connections based on the X19527 pinout:
- Pin 4 – Ground (Brown Wire – BR): This is a chassis ground.
- Pin 5 – Signal Ground (Brown/Orange Wire – BR/OR): This is another ground, often for sensor circuits.
- Pin 7 – K-Line (Violet/Yellow/Gray Wire – SW/VI/GE): This is the diagnostic communication line that connects to the DME.
- Pin 16 – +12V Power (Red/White Wire – RT/WS): This provides power to the OBD2 port. It should be “Hot at all times,” meaning it’s always powered, even when the ignition is off.
Alt text: OBD2 port pinout diagram X19527 showing pin numbers and descriptions for ground, signal ground, K-line, and +12V power, crucial for obd2 wiring.
Ground Connections (Pins 4 & 5)
For pins 4 and 5 (ground connections), the simplest approach is to connect them both to a single grounding point. You can use a ring terminal to join the brown and brown/orange wires together and secure them to a convenient chassis ground bolt, such as one of the bolts located above the ECU in the glovebox area.
Alt text: Close-up of ground wires, brown and brown/orange, connected to a ring terminal for secure chassis ground connection in obd2 wiring.
K-Line Connection (Pin 7)
Pin 7, the K-Line, is responsible for diagnostic communication. Locate the wire connected to pin 4 of connector X6031 on your M52/S52 harness. This wire (Violet/Yellow/Gray) originally runs to the underhood diagnostic connector. To route it to your glovebox OBD2 port, carefully pull this wire out of the harness bundle that crosses the firewall. Then, run this wire through the firewall, along with the DME harness bundle, and connect it to pin 7 of your X19527 OBD2 port connector.
Alt text: Illustration of K-line wire, violet/yellow/gray, being routed through the firewall alongside the DME harness for obd2 wiring to the glovebox.
+12V Power Connection (Pin 16)
For pin 16, which requires a constant +12V power supply, you’ll need to run a new wire. A good practice is to use a 5A fuse for protection. Connect a new wire to a 5A fuse in your E30’s auxiliary fuse box. Then, run this fused wire across to the glovebox area and through the firewall, again, ideally with the DME harness bundle for a clean installation. Connect the other end of this wire to pin 16 of your OBD2 port connector. This +12V source can be “hot at all times” or switched with the ignition, depending on your preference. While power could potentially be sourced from the X6002 connector, it’s often simpler and cleaner to run a dedicated fused line.
Alt text: Power wire, red/white, being connected to a 5A fuse in the auxiliary fuse box for providing constant +12V to the OBD2 port in obd2 wiring.
Important Note on ECU Flashing
Keep in mind that while this OBD2 wiring setup allows for diagnostics, flashing (reprogramming) the ECU requires an additional step. According to the ETM and resources like the OpenMS41 wiki, you must bridge pins 14 and 18 at the X6002 connector in addition to any bridging present in the diagnostic adapter cap itself. Refer to the OpenMS41 wiki for detailed information on enabling ECU writing capabilities.
Conclusion
By following these steps, you can successfully wire an OBD2 port into the glovebox of your E30 BMW with an M52/S52 engine swap. This modification provides convenient access for diagnostic scanning and, with the additional bridging mentioned, ECU flashing, enhancing the serviceability and tunability of your swapped E30. Always double-check your wiring and consult the relevant ETM pages for your specific model year for any variations. Remember to prioritize safety and disconnect the battery during any wiring work.
