Mitsubishi Repair & Maintenance Questions? Ask a Mechanic Online
Hi,The twin solenoids are nearly always the issue here. They are fired in parallel (one signal causes both to operate at the same time). Because of this, they are reverse in operation. One solenoid normally allows vacuum to pass, one solenoid normally blocks vacuum from passing. When the solenoid pack is fired, the conditions reverse.
For this reason, to properly test them you need to remove them from the car and check with a hand vacuum pump that one passes vacuum and the other holds 30inHg vacuum indefinitely. Then, apply voltage (battery voltage from the vehicle, or a 9V toy battery is sufficient) and verify that when energized the opposite results occur, the one that held vacuum releases entirely, and the one that passed vacuum holds 30inHg indefinitely.If either does not operate exactly like that (noting that even pulling 30inHg and then slowly slipping down is a fail), the 4WD will not work properly.There should always be vacuum to the solenoid pack. That is normal. If there is not, then trace your hoses looking for damage, or rust to the hard pipes/tank/etc.The switches can not be accessed through the tunnel. You need to lift the vehicle and remove the rear transmission support crossmember and slowly lower the tail end of the transmission to gain comfortable access. Being a 2006 it is highly unlikely that you have a switch issue though. While that used to be a thing, they updated the switches around 2003 or so and they rarely fail now... typically if they do it is a vehicle that is submerged very frequently etc.Your most likely culprit is typically the solenoid pack, followed by vacuum loss somewhere, then actuator failure. In my experience with these anyway. In the past 10-15 years I've probably changed 50+ solenoid packs, had a few dozen vacuum issues, and maybe 5 or so random switch problems (that weren't like 2000-era ones that had the sealing issues).