[greenberet123]

Not sure what is going on with my secondary air pump on my N51. I took it off and connected to a 12V battery and its running fine. Then I measured voltage across the connector after cold start - gives 12V for 20 seconds after cold start and then drops to 0, which is the correct behaviour I believe.

Now, when I plug the air pump back in, nothing. It freaking doesn't start. I'm out of ideas and perplexed. Help me fellow DIYers!

[gbalthrop]

I presume you mean the PUMP doesn't start, and NOT that the Engine doesn't start?
Two things are required for the pump to run:
1) 12V+ at Pin #2 (Black/Red/Yellow wire);
2) Continuity to Chassis Ground at Pin #1 (Brown wire to X166 Ground Point).
George

[greenberet123]

Originally Posted by gbalthrop

I presume you mean the PUMP doesn't start, and NOT that the Engine doesn't start?
Two things are required for the pump to run:
1) 12V+ at Pin #2 (Black/Red/Yellow wire);
2) Continuity to Chassis Ground at Pin #1 (Brown wire to X166 Ground Point).
George

I checked both of these with a multimeter and it checks out. I get +12 at pin2 and pin2 is connected to ground. This is so weird.

[gbalthrop]

If your Connector has BOTH 12V+ at Socket #2, and Continuity to Chassis Ground at Socket #1, AND your pump runs when you "Hot-wire" it, either the Connector sockets are NOT making contact with the Pump Pins, or there is an intermittent "open circuit" in the harness or pump.

Have you tried "Jumper connections" between Connector Sockets and Pump Pins, where you can confirm contact and "Jiggle-Test" the wiring harness? If you can rig such a "Jumper" setup, you can measure voltage between the two jumper wires (B+ & Ground).

Also, I assume you are aware the DME operates a Relay in the E-box for that short interval after cold start. There COULD be issue with the Relay, or with the wiring from the DME which Activates the Relay. If you need an ISTA Wiring Diagram, let me know the Last-7 Characters of your VIN.
George

[greenberet123]

So, super weird. I removed the relay and tested it separately and it was fine. Then I tested the pump outside again and it was fine. Then later I plugged it back in and suddenly it turned on when I started the car. This is bizarre. I just removed everything and put it back in the same way and now it works!

Originally Posted by gbalthrop

If your Connector has BOTH 12V+ at Socket #2, and Continuity to Chassis Ground at Socket #1, AND your pump runs when you "Hot-wire" it, either the Connector sockets are NOT making contact with the Pump Pins, or there is an intermittent "open circuit" in the harness or pump.

Have you tried "Jumper connections" between Connector Sockets and Pump Pins, where you can confirm contact and "Jiggle-Test" the wiring harness? If you can rig such a "Jumper" setup, you can measure voltage between the two jumper wires (B+ & Ground).

Also, I assume you are aware the DME operates a Relay in the E-box for that short interval after cold start. There COULD be issue with the Relay, or with the wiring from the DME which Activates the Relay. If you need an ISTA Wiring Diagram, let me know the Last-7 Characters of your VIN.
George

[gbalthrop]

Most likely an issue with relay activation. The pin for voltage supply to the coil electromagnet, OR the pin for switched ground to that electromagnet don't carry that much current, and if corroded, or loose connection, "Electrickity" happens.
George