Diagnostic Procedures

Mitsubishi, Colt and Hyundai trans-axles with vacuum control.

The KM162, KM163 and KM182 transmissions use a vacuum actuator to shift the input shaft gear set. When the driver shifts into 1st, 2nd 3rd, 4th or reverse the vacuum is drawn at the front of the select actuator. When the driver shifts into 5th the vacuum changes to the rear. The transaxle is still in 4th, but is overdriven by the input gear set.

The components used to control the actuator are external of the transaxle. They are the select switch, backup light switch, select control solenoid and select control unit (SCU).

If you have problems, such as no movement, no 5th, 4-5-4 shuttle shifts, or lack of power from stops, be sure to check the external controls!

First, check the input gear by removing the two bolts that attach the select actuator and giving it a good firm tug. This will manually shift the transaxle into high range. Drive the car. You should have four high range gears (the highest is actually high range 5th). If these gears are OK remove the actuator entirely and shove the selector into the low range. Drive the car again, if you have four properly working normal range gears the transaxle is fine, your problem is external!

The select solenoid is controlled by the SCU, it moves the vacuum from the front to rear hose. Be sure the hoses are not reversed, causing 4th gear to drive like 5th & vice versa. A bad select solenoid can cause no movement.

The select switch sends a +12 volt signal to the SCU when the driver shifts into 5th or reverse. Be sure the mark on the switch is aligned to the mark on the case! A bad or misaligned select switch can cause a shuttle shift or a no 5th condition.

The backup light switch sends a +12 volt signal to the SCU when the driver shifts into reverse. If the backup light switch is bad or if the steel ball that goes into the case before you install the switch is missing, you may have no 5th or overdrive in reverse.

The SCU will energize the select solenoid only when the select switch is closed and the backup light switch is open. Some SCUs get additional signals from the alternator and/or speed sensor. If you suspect a SCU problem first check all external leads, then follow recommended factory test procedures.

TRANSMISSION EXCHANGE CO is located at 1803 NE MLKing Blvd., Portland, OR 97212. Ph. 503-284-0768, 800-776-1191 Fax 503-280-1655 E-mail