Performing an engine swap, especially when integrating a modern OBDII engine into a classic chassis, requires meticulous attention to wiring, particularly for the check engine light. This guide provides a detailed wiring diagram and pinout information to ensure your check engine light functions correctly after an engine swap. Proper wiring is crucial not only for the check engine light but also for overall engine management system functionality.
Understanding the connections between your OBDII engine harness and your vehicle’s existing wiring is essential. This document focuses on integrating an OBDII engine, often found in BMW E36 models and later, into an older chassis, such as the BMW E30. We will outline the necessary wire connections, focusing on key connectors like C101, X20, and X6031 to properly hook up your check engine light and related systems.
Below are the pinouts and wiring details to help you successfully complete your engine swap and ensure your check engine light is properly wired.
Connector C101 Pinout
This connector is a key interface in integrating the engine harness with the chassis.
| Pin | Wire Color | Description |
|---|---|---|
| 1 | Blue | Alternator + |
| 2 | Green/Yellow | Oil level sensor full |
| 3 | Empty | Empty |
| 4 | Brown/Purple | Cluster temperature gauge |
| 5 | Brown/Green | Oil pressure switch |
| 6 | Green/White | o2 sensor relay (not needed) |
| 7 | Green | Ignition switch power constant |
| 8 | Black/White | Economy gauge |
| 9 | Black | RPM signal |
| 10 | Blue | Oil level sensor low |
| 11 | White/Green | Service indicator reset |
| 12 | Gray | Check engine Light |
| 13 | Green/Purple | Fuel pump relay |
| 14 | Black/White | Vehicle speed sensor from cluster |
| 15 | Black/Green | Unloader relay |
| 16 | Black/White | srs diagnostic wiring |
| 17 | Empty | Abs communication for ix |
| 18 | Black/Yellow | Ignition switch starter |
| 19 | Empty | m3 oil temp (unused) |
| 20 | Red/Yellow | abs relay power for 1990+ cars |
Connector X20 Pinout
The X20 connector is another critical point for integrating various engine and chassis systems.
| Pin | Wire Color | Description |
|---|---|---|
| 1 | abs/asc? | |
| 2 | abs/asc? | |
| 3 | Green / violet | Exhaust flap solenoid (unused for e30) |
| 4 | Black/ blue | a/c compressor cntrl relay (unused) |
| 5 | Black/gray | a/c pressure switch (unused for e30) |
| 6 | purple/gray | Climate control module (unused for e30) |
| 7 | Green | EWS (Unused for e30) |
| 8 | red/white | pws for carbon canister/exhaust flap (unused) |
| 9 | Brown/red | Vss input (normally from ASC module) |
| 10 | Reserve light switch | |
| 11 | Brown/yellow | Engine temp sender to gauge cluster |
| 12 | Brown/purple | Engine temp sender to gauge cluster |
| 13 | Green/purple | Fuel pump relay |
| 14 | Empty | empty |
| 15 | Black/green | Starter motor side? |
| 16 | White/yellow | to pin 15/20 diagnostic connector |
| 17 | White/purple | to pin 20/20 diagnostic connector |
| 18 | Black/yellow | Starter engage |
| 19 | White/green | Service indicator reset |
| 20 | Black | Engine speed |
| 21 | Green | constant power with ignition on |
| 22 | to pin 16/20 diagnostic connector | |
| 23 | Brown/green | Oil pressure switch |
| 24 | black/white | Fuel economy gauge |
| 25 | blue | alternator signal |
Connector X6031 Pinout (OBDII Diagnostic Connector)
This is the OBDII diagnostic connector, crucial for check engine light functionality and diagnostics.
| Pin | Wire Color | Description |
|---|---|---|
| 1 | Gray | Check engine light |
| 2 | Green/blue | Carbon canister (unused for e30) |
| 3 | Green/red | Fuel consumption signal (unused for e30) |
| 4 | white/purple/yellow dots | OBD to Diagnostic connector(unused for e30) |
| 5 | yellow/red | Fuel tank pressure sensor (unused for e30) |
| 6 | red/green-gray/white | Fuel tank pressure sensor (unused for e30) |
| 7 | Brown/black | Fuel tank pressure sensor (unused for e30) |
| 8 | Pupple/black | Power for DLC |
| 9 | empty | empty |
| 10 | empty | empty |
| 11 | empty | empty |
| 12 | empty | empty |
C101 to X20 Wiring Connections for Engine Swap
Here’s how to connect wires from the C101 connector to the X20 connector during your engine swap.
| C101 Pin | X20 Pin | Description |
|---|---|---|
| 1 | 25 | Alternator signal |
| 2 | N/A | Oil level sensor (No direct X20 pin. Requires custom wiring or repurposing an unused wire on the engine harness side) |
| 4 | 12 | Cluster temperature gauge (Rewire brown/purple to new E30 temp sensor) |
| 5 | 23 | Oil pressure switch |
| 7 | 21 | Ignition switch power constant |
| 8 | 24 | Fuel economy gauge |
| 9 | 20 | Engine rpm speed |
| 11 | 19 | Service indicator reset |
| 12 | 1 (X6031) | Check engine light (Connect C101 Pin 12 Gray wire to X6031 Pin 1 Gray wire on the OBDII diagnostic connector to enable the check engine light function) |
| 13 | 13 | Fuel pump relay |
| 14 | 9 | VSS input from cluster |
| 16 | 8 (X6031) | Power for DLC (Connect C101 Pin 16 Black/white wire to X6031 Pin 8 Purple/black wire to provide power to the OBDII diagnostic connector) |
| 18 | 18 | Starter engage |
| 20 | N/A | Power from DME relay for 90+ cars (For 88-89, leave empty. For 90+, wire to a red/white wire in the harness. Verify wire color on chassis side. If brown DO NOT wire to power. Verify with wiring diagrams.) |
Ensuring Check Engine Light Functionality
The check engine light wiring is critical for diagnosing engine issues after your swap. As highlighted in the tables, connect the Gray wire from C101 Pin 12 to the Gray wire on X6031 Pin 1 of your OBDII diagnostic connector. This connection is what enables the check engine light to function with your swapped engine’s ECU.
By carefully following this wiring diagram and pinout guide, you can confidently wire your OBDII engine into your older vehicle, ensuring proper functionality of essential systems, including the all-important check engine light. Always double-check your wiring against your specific vehicle and engine wiring diagrams to guarantee accuracy and avoid potential electrical issues.
