Keep Those Trannys Rolling - June - 2019

Diagnosing Subaru’s Shift Lock System

In this issue of “Keep Those Trannys Rolling”, we are going to take a look at a “Key Stuck in Ignition” problem on a 2015 Subaru Outback. This 2015 Subaru Outback was at a shop and is equipped with a 2.5l engine, a TR580 CVT transmission, a floor shifter assembly and does not have the “Push to Start/ Stop” option. The customer may also state that the problem is intermittent.

The story goes like this; the customer arrived at the shop and said he had been unable to remove the key from the ignition cylinder for the last couple of days. The customer indicated that he had already been to a couple of other shops for a diagnosis. Both shops thought that the concern was related to the transmission and referred him to a local transmission shop for repair.

DUPLICATE THE CONCERN:

On the initial inspection, we found the ignition key was indeed, stuck in the ignition cylinder and the key cylinder could not be rotated back to the lock position (figure 1). We visually inspected the shift cable and verified that it was working properly. We disconnected the shift cable from the transmission to see if we could rotate the lock cylinder back to its park position, and we could not. This was an indication that we were experiencing a shift lock system concern and not an internal transmission concern.

SUBARU’S SHIFT LOCK SYSTEM:

The purpose of Subaru’s shift lock system is to prevent the shifter lever from coming out of the “Park” position and the ignition key from being removed from the ignition cylinder without specific inputs from the driver, such as, the ignition key is on, the stop lamp switch depressed and shifter lever in park.

Subaru’s shift lock system consists of:

  • the ignition switch
  • relays
  • stop lamp switch
  • key warning switch
  • a key lock solenoid
  • a shift lock solenoid
  • a “P”(park) range switch
  • a VDC CM (vss sensor)
  • wiring
  • connections
  • the TCM
  • a Body Integrated Unit (BIU) to control the shift lock system

SUBARU’S SHIFT LOCK SUB-SYSTEMS:

Subaru’s shift lock system consists of two different sub-systems within the shift lock system. They are:

  • Ignition Cylinder Lock System: The ignition cylinder lock subsystem consists of the “P” (park) range switch, key warning switch and the key lock cylinder.
  • Shift Lever Lock System: The Shift Lever Lock system consists of the shifter lever assembly (referred to as “Select Lever Complete”), the stop lamp switch, and the shift lock solenoid.

Both sub-systems are controlled by the Body Integrated Unit (BIU).

HOW DOES THE IGNITION CYLINDER LOCK SYSTEM WORK?

When the ignition switch is on, and the shifter lever is in the park position, the Body Integrated Unit monitors the “P” (park) range switch (located in the shifter lever assembly) operation by sending a 12vdc low amp current to the “P” range switch. When the shifter lever is placed in the park position, the “P” range switch circuit will go to ground. If the Body Integrated Unit does not see the “P” range switch circuit go to ground, the Body Integrated Unit will disable the shift lock system. If this happens, the Body Integrated Unit will not energize the key lock cylinder and allow the key cylinder to be rotated back to the lock position, which allows the ignition key to be removed from the lock cylinder.

HOW DOES THE SHIFT LEVER LOCK SYSTEM WORK?

When the ignition switch is on and the shifter lever is in the park position, the Body Integrated Unit monitors the stop lamp switch operation by sending a 12vdc low amp current to the stop lamp switch. When the stop lamp switch is depressed, the stop lamp switch circuit will go to ground. When the Body Integrated Unit sees the stop lamp switch go to ground, it energizes the shift lock solenoid (located in shifter lever assy), allowing the shifter lever to be removed from the park position. If the Body Integrated Unit does not see the stop lamp switch circuit go to ground, it will not energize the shift lock solenoid, thereby locking the shifter lever in the park position.

DIAGNOSING SUBARU’S SHIFT LEVER LOCK SYSTEM:

After a visual inspection of wiring and connections, check the stop lamps (brake lights) operation. If the brake lights are not working, check fuse #37 (7.5amp) located in left kick panel fuse & relay box. If fuse #37 is okay, check for power at the stop lamp switch pin #1. If pin #1 has 12vdc, check for a good ground circuit on pin #3. If the stop lamp switch has good power and grounds, check the stop lamp switch continuity during stop lamp switch application. If stop lamp switch is okay or if brake lights system is working properly, check for 12vdc at pin #3 and ground at pin #4 of the shifter lever assembly (figure 3).

If shifter lever assembly power and grounds are okay, energize shift lock solenoid & listen for click. If shift lock solenoid clicks, check Body Integrated Unit power and grounds. If power and grounds are okay, suspect a possible faulty Body Integrated unit. If shift lock solenoid does not click, replace shifter lever assembly (select lever complete).

DIAGNOSING SUBARU’S IGNITION CYLINDER LOCK SYSTEM:

After a visual inspection of wiring and connections, check the “P” range switch circuit for 12vdc at the shifter lever assembly pin #1 (with key on) and the ground circuit on pin #2 (figure 2). If the shifter lever assy has power on pin #1 and has a good ground circuit on pin #2, check for “P” range switch continuity in Park. If the “P” range switch has continuity in park only, the “P” range switch circuit is working properly.