I’ve seen a lot of wiring issues with engine swaps, things not working, and things not working correctly, etc.. A lot of that comes down to not knowing or understanding the wire functions that are coming out of c101 and what the e30 is really looking for and what it is giving to the engine harness. So below is a the e30 pin out for c101 and a description of what each pin does and what it should connect to on the engine side. Of course you should always check the ETM for your year and model as well as verifying what you have in your own car before you use any of this information.
Pin No. – Wire color (for the body side of the connector) – Signal - Description
Pin#1-Blue - D+ - Wire is connected to the D+ terminal of the alternator then goes through c101 to the cluster. The dash light gets its power from the ignition switch in run or start then to c101 and then to the alt. This pin must be connected at all times or the alternator will not charge the battery after engine start. BMW seems to have standardized the color coding for this signal to always be blue (at least it is in the e30, e36, e46, e39, etc.) In most cases this wire goes straight from the alternator to c101, but in newer models ~2000+ it goes to the DME first and is then passed on to the car.
Pin#2 – Blue/Violet or Blue/Black – Oil Level (STATIC) – This connection is almost exclusive to the e30. The sole purpose of this is to provide one half of the signal necessary for the Check Control Panel to determine whether or not to illuminate the “Low Oil Level” light. Signal comes from Pin 2 of the 3 pin oil level sensor in the oil pan directly to c101 then on to the Check control panel.. Pin 1 of the oil level sensor is for a ground.
Pin#3 – No connection
Pin#4 – Br/Vi – Water temp – This is the signal wire for the e30 clusters water temp gauge. The e30 sensor should be grounded to the engine. The terminal on the sensor should be connected to a wire that connects directly to c101. From there it goes straight to the cluster temp gauge. This sensor is not used by the DME at all. For an accurate temp gauge the correct e30 temp sensor must be used.
Pin#5 – Black/Brown – Oil Pressure Switch - Wire is connected to the oil pressure switch on the engine where it is grounded. The other end is attached directly to the clusters red oil pressure light. 12v is supplied to the light in the cluster, when the oil pressure dips below 0.4 bar the sensor grounds out, completing the circuit and turning on the light. .) In most cases this wire goes straight from the oil pressure switch to c101, but in newer models ~2000+ it goes to the DME first and is then passed on to the car.
Pin#6 – Green/Yellow – Fused B+ - This connection is 12V when the ignition switch is in Run or Start position. Power from the battery goes through the ignition switch, is passed through Fuse 9 and then to c101. In the e30 engine harness it is used to power the o2 heater relay, the idle control module, cold start valve, etc.. By the time the m20b25 came in most of these functions were taken up by the DME or not needed and this pin was only used for the o2 relay heater. In a swap this pin should be used anytime a switch 12v, fused supply is needed. For example ECU turn on signal.
Pin No. – Wire color (for the body side of the connector) – Signal - Description
Pin#1-Blue - D+ - Wire is connected to the D+ terminal of the alternator then goes through c101 to the cluster. The dash light gets its power from the ignition switch in run or start then to c101 and then to the alt. This pin must be connected at all times or the alternator will not charge the battery after engine start. BMW seems to have standardized the color coding for this signal to always be blue (at least it is in the e30, e36, e46, e39, etc.) In most cases this wire goes straight from the alternator to c101, but in newer models ~2000+ it goes to the DME first and is then passed on to the car.
Pin#2 – Blue/Violet or Blue/Black – Oil Level (STATIC) – This connection is almost exclusive to the e30. The sole purpose of this is to provide one half of the signal necessary for the Check Control Panel to determine whether or not to illuminate the “Low Oil Level” light. Signal comes from Pin 2 of the 3 pin oil level sensor in the oil pan directly to c101 then on to the Check control panel.. Pin 1 of the oil level sensor is for a ground.
Pin#3 – No connection
Pin#4 – Br/Vi – Water temp – This is the signal wire for the e30 clusters water temp gauge. The e30 sensor should be grounded to the engine. The terminal on the sensor should be connected to a wire that connects directly to c101. From there it goes straight to the cluster temp gauge. This sensor is not used by the DME at all. For an accurate temp gauge the correct e30 temp sensor must be used.
Pin#5 – Black/Brown – Oil Pressure Switch - Wire is connected to the oil pressure switch on the engine where it is grounded. The other end is attached directly to the clusters red oil pressure light. 12v is supplied to the light in the cluster, when the oil pressure dips below 0.4 bar the sensor grounds out, completing the circuit and turning on the light. .) In most cases this wire goes straight from the oil pressure switch to c101, but in newer models ~2000+ it goes to the DME first and is then passed on to the car.
Pin#6 – Green/Yellow – Fused B+ - This connection is 12V when the ignition switch is in Run or Start position. Power from the battery goes through the ignition switch, is passed through Fuse 9 and then to c101. In the e30 engine harness it is used to power the o2 heater relay, the idle control module, cold start valve, etc.. By the time the m20b25 came in most of these functions were taken up by the DME or not needed and this pin was only used for the o2 relay heater. In a swap this pin should be used anytime a switch 12v, fused supply is needed. For example ECU turn on signal.
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