DTC P0872: Short in 4th Clutch Transmission Fluid Pressure Switch Circuit, or 4th Clutch Transmission Fluid Pressure Switch Stuck ON
The easiest-proper diagnostic is to use a capable scan tool.....Key-on Engine-off
*Monitor the 4th clutch pressure switch On/Off PID.
*If it reads "Yes", Unplug the the pressure switch.
*If it now reads "No"......Replace pressure switch.
*If it reads "Yes" with the pressure switch unplugged. The pressure switch circuit is most likely shorted to ground.
Alternate procedure......
*Locate the 4th pressure switch connector & disconnect it from the switch
*Key-on Engine-off.......Probe the connector terminal (Blue/Yellow wire) with a DVOM hooked to ground.
*It should read @ 5 volts if the circuit is not shorted to ground.
The pressure switch isn't the easiest to access with the battery & battery tray in the way, For diagnostic purposes.....I use 2 10 gauge jumper wires hooked & taped (Tape them well to prevent shorting while working!!) to the battery cable terminals & connect the jumpers to the battery on the floor out of the way.