ground wire

[Markus]

I removed the upper and lower intakes along with the valve covers to degrease them and repaint the covers along with other cleaning and wire loom repair. After I got everything back together weeks later due to a lot of reading and YT videos on various automotive stuff I noticed this brown ground terminal wire unattached and I don't recall removing that as it's halfway down the loom that carries the 02 sensor wires, basically coming out near where the ignition module harness wires come out of a different larger trunk.

The other brown in that 02 sensor loom that goes to the sensor is a ground which I checked for continuity and since this one has a ground terminal on it I can only assume it was connected to a ground bolt somewhere. The wire in question only has about six inches of wire showing from where it exits the loom. Was that connected to the rear left lower intake bolt because that seems to be the only location it could comfortably reach?

I just don't recall removing it and wouldn't think it would be attached there but I don't see anywhere else it would go. Also, what is that a ground for, it seems to be running back to the ECA because I found continuity when back probing one of the two round connectors near the passenger side valve covers that has a brown wire going to it. These seem to lead back along that trunk on the passenger side that probably goes to the ECA.

 

[adsm08]

It gets bolted to the back of the head. It is very important. It's an O2 sensor ground and without it the computer can't see the signal from that sensor.

 

[Markus]

Roger that

Thanks for the reply. I already found that the brown in the connector is going to ground so is this second brown wire with the terminal acting as a second ground for some reason I don't understand? Monday I'll double check some connections and take a pic of the four wires without the loom if it helps to clarify any other questions.

Also it should be noted that my original wiring colors are completely different from the electrical book colors for this circuit. The book states GY/Y (ignition switch), DG/P (pin 29) and BK/LG (ground) whereas my truck is BK/R, R/W and the ground is BR.

 

[adsm08]

Your O2 sensor has two grounds that need to be seperate from each other.

The one that you found in the connector is for the heater element. Oxygen sensors don't read all that accurately below about 400*F, so to get them up to temp and working ASAP they put a heater element in them. That obviously needs a power and a ground.

The other wire in your connector sends the voltage that sensor makes back to the computer, but without that circuit grounded the computer can't see is going on.

In newer vehicles both sides of the circuit run directly from the sensor to the computer because it gives a cleaner signal which helps dial in the fuel mix a little better, so better MPG and cleaner emissions.

 

[Markus]

Thanks again for an even more detailed answer, I'm finally getting to know this truck in a more intelligent way due to people like you and having the electrical book.I did trace that wire to pin 49 on the ECU. The wire I said that was R/W is actually BL/W for those who read this and have a similar setup.