What is this wire for?

[vpilarrt]

Sorry to thread jack, how do you tell which plug goes to which sensor? Trial and error?

One of the coolant temp plugs has 2 contacts, the other has 1 - so that's easy to fugure out. If you plug the oil pressure connector onto the coolant sensor and visa-versa you will get obviously incorrect engine temp readings and the oil pressure warning light will be on.

[vpilarrt]

Yes, since the sensor is pre-catalyst you should leave the wire plugged in if you do have a sensor installed.

No. If you have an O2 sensor you want this wire disconnected.

[bluevanilla]

Who are you? Did you have the same problem or did you log in under another name?

I could have same problem because I have an e30 with m42 engine.

[roguetoaster]

Just checked last night, it was not connected. :up:

Who are you? Did you have the same problem or did you log in under another name?

[bluevanilla]

Just checked last night, it was not connected. :up:

[roguetoaster]

Sorry to thread jack, how do you tell which plug goes to which sensor? Trial and error?

Look at the lengths of wire/the bends in the wire, that will generally tell you which one goes to the oil pressure sensor and which two go to the head. Then the coolant plugs will be differentiated by the number of "sockets" for pins on the plug itself, as one has two and the other has one. Further, on my cars the forward coolant plug is grey, the aft is black.

Thus, of the two black plugs, the two pin one goes to oil pressure, the one pin goes to the orange/red/brown sensor on the head, and the grey plug goes to the blue two pin sensor forward on the head.

Got it? Good.

If you are working from a wiring harness out of the car I would say to start with a pin out of the DME and then continuity test the plugs.

TLDR (if your car is the same as mine):

black two pin connector = oil pressure
black one pin connector = rear sensor on head, one pin, redish/browinsh in color
grey two pin connector = front sensor on head, two pin, blue sensor

[chodedub]

I knew this topic would be about this wire / plug...
Everything has been said, I will just add this picture, check bottom left

Sorry to thread jack, how do you tell which plug goes to which sensor? Trial and error?

[roguetoaster]

Yes, since the sensor is pre-catalyst you should leave the wire plugged in if you do have a sensor installed.

Either look under the car or follow the wire under the battery tray in the engine compartment to the sensor.

[DER E30]

Hmmm, I'm catless but presumably have an o2 so leave it alone?

[roguetoaster]

So with no cat I should have it plugged in?

As long as you have no O2 sensor.

AFAIK there is no difference in the DME, as both a "euro" and US version have the same P/N.

[ck_taft325is]

So with no cat I should have it plugged in?

Presumably.

[DER E30]

So with no cat I should have it plugged in?

[JNSmith1717]

Amazingly my car runs better now

[george graves]

Wouldn't it be best (if you had it plugged in) to unplug it, and reset the ecu and let it re-learn?

[JNSmith1717]

Hhmm had a weird feeling to look into this thread, sure enough mines plug in too