I've been searching for an answer for an hour now with no luck. The car is a 90 4runner 3.0 manual 4wd. There is a factory wire running to the ECU labled 4wd. What does that do? Does the ECU have a 4wd mode that sacrifices mpg for power or something? Shifting to 4wd in the 2nd gen is all mechanical so why would the ECU need to know?

Also how does it change state? Ground on/off, + voltage on/off?

I'm trying to eliminate the last of the gremlins in my rig. Someone in an ABS delete thread mentioned deleting ABS may cause the ECU to go into "4wd mode". That got me started down this path. Don't know what that is or if I even want my ECU to ever go into "4wd mode".

 

I think it stops the fuel cut off from cutting off?

 

I tested the wire at the ECU. I'm getting +12v in 2wd and 0v in 4wd. But I'm not sure if that is the way it's supposed to be. I've been fixing some electrical mistakes caused by previous owners.

 

If you look at the diagram you will see it simply has the 4wd switch between the ECU and a ground connection. So yes it seems to be wired correctly.

As to its functionality inside the ECM, I don't see any reference to it in the TCCS book other than it exists as a groundable switch input.