Keep Those Trannys Rolling - April - 2019

Ford’s Park Detect System

In this issue of Keep Those Trannys Rolling, we’re going to take a look at a 2015 Ford Explorer with a “Transmission Not in Park” message displayed in the Message Center of the Instrument Panel Center (IPC), and the Shift to Park light is on.

Our 2015 Ford Explorer is equipped with a 3.5 L engine, a 6F55 transmission, a floor shifter, and has the Push to Start/Stop option. Our Explorer was towed into the shop because it had a dead battery. The customer indicated that he’d been experiencing starting problems (slow cranking) over the past couple of weeks, until the vehicle wouldn’t start.

INITIAL INSPECTION

On initial inspection, the battery voltage was low (less than 10VDC). The technician cleaned and serviced the battery, cleaning battery cable connections and checking battery electrolyte levels. He charged the battery back to specification (13.5 VDC) and started the vehicle.

The charging system was working properly with a charging voltage of 14.5 VDC. He checked the battery for a draw or drain on the system. There were none. After a thorough inspection of the battery and charging system with no problems found, the shop returned the vehicle to the customer.

RETURN VISIT

About a week later, the customer called the shop, indicating that he was still having problems starting the engine after being parked for a long time (overnight or over the weekend). The customer said he was able to start the engine this morning and that he was going to stop by the shop to have the battery and charging system rechecked.

The customer showed up a couple hours later and indicated that the engine had no problems starting after this morning’s initial start-up. The customer then indicated there was a light on the dash that has been coming on from time to time and a message “transmission not in park” displayed in the message center.

The customer moved the shifter lever around (in/out of park) a couple times to get the light to go out. He agreed to leave the vehicle so the shop technician could try to duplicate the conditions.

DUPLICATE TO DIAGNOSE

After several test drives with the vehicle, the technician was able to get the light to come on and to have the “Transmission Not in Park” message displayed in the message center.

Turn out the light on the dash is a Shift to Park warning light and the message center indicated that the transmission was not in park. So they decided to look at the transmission control system, shift linkage or cable, shifter lever, and transmission range switch operation.

After further inspection, they found that the “Shift to Park” warning light would stay on after the vehicle had been shut off, causing a draw or drain on the battery system, which caused the battery to go dead after the vehicle had been parked for extended periods of time.

They connected a scan tool to the DLC to check for any codes in the computer system. There were no codes in any of the on-board systems. Then they monitored the transmission range switch input to the PCM. The transmission range switch PIDs in the PCM was correct and the PRNDL display in the Instrument panel cluster was correct, even though the “Shift to Park” light was lit and the message center was indicating that the transmission wasn’t in park (figure 1).

With the PCM transmission range switch PID and the PRNDL display correct, it was time to look into the Park Detect system to try to locate the problem.

HOW THE PARK DETECT SYSTEM WORKS

The Park Detect system consists of the Instrument Panel Cluster (IPC), the Powertrain Control Module (PCM), the Body Control Module (BCM), the transmission range switch, the shifter lever assembly, the HS CAN data lines, and related wiring and connections.

The Park Detect system uses the transmission range switch input to the Powertrain Control Module. The Powertrain Control Module uses the HS CAN data line system to share the transmission range switch data with the Body Control Module. The Body Control Module then shares that information with the Instrument Panel Cluster (also using HS Can data lines) to control the PRNDL display within the Instrument Panel Cluster.

The Instrument Panel Cluster compares the data from the Powertrain Control Module, the Body Control Module, and the Park Detect switch (located in the shifter lever assembly) to verify that the transmission is indeed in park.

If the Instrument Panel Cluster detects a discrepancy between the PRNDL display and the Park Detect switch position, the Instrument Panel Cluster message center will alert the driver that the transmission isn’t in park and the Body Control Module will light the Shift to Park warning light.

HOW THE PARK DETECT SWITCH WORKS

The Park Detect switch is an integrated part of the floor shifter lever assembly. The Instrument Panel Cluster provides a battery reference voltage to the Park Detect switch circuit.

When the shifter lever is in park, the Park Detect switch sends the reference voltage to ground. When you move the shifter lever out of park, the Park Detect switch interrupts the ground circuit, indicating the shifter lever is no longer in park.

DIAGNOSING THE PARK DETECT SYSTEM

Diagnosing the Park Detect system is pretty straightforward. (Refer to your specific vehicle information for connector terminal information and system wiring schematics).

  • Check the battery condition and connections.
  • Connect your scan tool to the DLC and check all on-board computer systems for codes.
  • Repair any codes related to the transmission range switch, HS CAN data lines, or communication system before diagnosing the Park Detect system.
  • Visually inspect the PRNDL display to verify proper operation.
  • If the PRNDL display is erratic or doesn’t display park, check the transmission range switch PIDs in the Powertrain Control Module. If the transmission range switch PIDS are erratic, check and repair the transmission range switch circuit.
  • If transmission range switch PIDs are correct in the Powertrain Control Module, check transmission range switch PIDs in the Body Control Module. If the transmission range switch PIDs are correct in the Body Control Module and the PRNDL display is still erratic, perform Instrument Panel Cluster self-test to determine if PRNDL display is faulty.
  • If PRNDL display is faulty, replace the Instrument Panel Cluster.
  • If PRNDL display is correct, check the Park Detect switch circuit, wiring, and connections. Repair as needed (figure 2).
  • Check the Park Detect PID in Instrument Panel Cluster. If there’s no change while moving the shifter in and out of park position, check battery reference voltage at the Instrument Panel Cluster terminal 7 (green wire; figure 3). If no or low voltage:
    • Check the Instrument Panel Cluster power and grounds. Check for a possible faulty Instrument Panel Cluster assembly. Replace or repair as needed.
    • If the Instrument Panel Cluster is supplying battery reference voltage to the Park Detect switch circuit, check the Park Detect switch operation (located in shifter lever assembly).
  • If the Park Detect switch is working properly, check the Park Detect switch ground circuit, and repair as needed (figure 4).
  • If the Park Detect switch isn’t working properly, replace the shifter lever assembly (figure 5) and recheck the Park Detect system operation.

Well, there you have it. We’ve taken a quick look at Ford’s Park Detect system. With a better understanding of how the system works, you should have no problem keeping those trannys rolling down the road.