Safety Switch Repair Procedure
Because mis-alignment, corrosion, and dust or water entering
the Shift Position Sensing Unit (AKA Neutral Safety) switch can cause a
multitude of malfunctions of the AW4 automatic transmission, it is a good
idea to check it out before assuming you have a bad transmission or Transmission
Control Unit. These problems may be intermittent so can be very hard to pin down
at times. The switch is quite expensive to purchase a new one, but is
easily adjusted or taken apart and cleaned.
You can check out the switch before removing it from the
transmission by using a ohmmeter at the plug where it connects to the wiring
harness. The plug is located on the passenger side of the engine compartment
next to the firewall. You should read continuity according to the instructions below.
If you read any resistance and not total continuity in any of the pins on the
plug when moving the shift lever then remove the switch and clean it. Be
sure you are on level ground with the parking brake set, the wheels blocked, and
engine off prior to
testing or removal of the switch. The instructions from the Cherokee Repair
manual for removal, replacement and adjustment are found below.
Note: Part of the switch housing is a plastic
material. When removing the switch it may be hard to slide off of the
shaft because of a build up of dirt and corrosion. You may want to spray
it with a penetrating oil and let it set for a while before trying to remove
it. Be careful when prying it off of the shaft or the plastic housing may
The pictures of the disassembled switch are courtesy of
Frank Barnes, who had installed the CompuShift Plus but still had shift
problems. I suggested to him that it might be the 1-2 position switch on
the transmission that was causing him problems so he said he would check
it. What he found is that the switch was, as he put it, "full of
crap" and was causing intermittent transmission and backup light
Because of the fact that the switch has eight separate contacts
and two sets of wipers you can have problems in only one area of the switch and
circuit while everything else functions fine. So you cannot just assume
that if it starts ok in park or neutral that all of the rest of the contacts are
The switch is held together by Phillips screws and is not sealed
so it can be taken apart quite easily. After removing the screws it is a
simple matter of removing the wiper arm and its two springs and contacts.
You can then use a contact cleaner to spray both halves of the switch assembly
taking care to make sure that all the contact surfaces on it and the wiper arm
are clean and bare. Replace the springs and contacts into the wiper arm and
reassemble it to the case with the contacts on the wiper arm facing the contacts
on the wired side of the assembly then apply a light lube or grease to the arm
where it goes through the hole in the other half of the assembly and also to the
back side of it (opposite the contacts) where it rides on the assembly case.
Take care not to get any on the contacts themselves. If you wish use a light
silicone or other sealant on the edges of the case before tightening the screws.
This will help to keep out any new contamination. Re-install and adjust
the switch according to the directions below.
Disassembled Neutral Safety/Back Up and 1-2 Switch
Transmission Position Sensing Unit Connector.