Shift Pointers
- Subject: Preventing ground-related problems
- Unit: Subaru 4AT phase 2
- Essential Reading: Rebuilder, Diagnostician
- Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor
We all know how important grounds are in an electrical system, and when it comes to our trade we can tell incident after incident of weird, unexplainable transmission malfunctions that are taking on “fish story” proportions. And, in fact, we have caught quite a few large ones over the years.
How about catching a small fish before it gets too big? You need to be aware of a ground used in Subaru vehicles with the newer 4AT phase 2 transmission.
In the typical wiring diagram below, notice that the ground wire for the transmission control module is inside the transmission, where it also is used for the solenoids.
Figures 1 and 2 show you the location of this ground. As you can see, it is a typical wire with an eyelet attachment.
This is one vulnerable area, and the other is in the harness connector (see Figure 3). The No. 16 terminal in the connector is where this ground wire passes through to the TCM. It is imperative to pay close attention to this ground wire, making sure that it has not been compromised in any way.
No doubt this could turn into a big fish story of TCM crazies causing erratic behavior and a host of codes. Get it hooked before it gets away!
