The Transmission Range Sensor (TRS) has 3 primary functions:
- Provide a PARK/NEUTRAL start signal to the engine controller and the starter relay.
- Turn the Back-up lamps on when the transmission is in REVERSE and the engine (ignition) is on.
- Provide a transmission range signal to the instrument cluster.
This relatively simple sensor has caused us problems over the years.
In one case, right after a fresh install at our Lincoln store, they had an alarming problem. With the vehicle running and in the park position, if you took your foot off of the brake, or opened the door to get out, the horn would start honking and the headlights would start flashing.
They also noticed that the indicator lights weren?t functioning correctly. When they put the vehicle into park position the ?P? on the indicator would not light up. This condition was not there with the original unit.
They pulled the pan and found that the Neutral Switch pin that rides on the rooster comb was not contacting the comb when in the park position. This was a late model unit and used the range sensor style switch.
The issue was that the bracket between the case and the adapter had two washers installed between the adapter and the case. This moved the sensor too far from the rooster comb.
The computer could not sense that the vehicle was in park and triggered the out of park alarm.
Proper installation is: one washer on both sides of the bracket (see figure 1). This unit had three washer with two installed between the bracket and case. Removing one of the washers next to the case corrected the problem. You also should be careful when replacing the TRS mounting (see figure 2) bracket.
Any damage or miss assembly of the bracket can also cause the TRS to give a faulty reading.
The linear motion of the TRS is so short that a few thousands of an inch is enough to cause the TRS to not read properly.
When installing the TRS mounting bracket, torque the bracket to 25 feet lbs. using the Chrysler adapter # 8581 or equivalent.
The two screws that hold the TRS to the bracket torque is 30 inch lbs.
Another complaint we?ve seen with this set-up is no Park or you are unable to move the shifter linkage all the way into the Park position.
If you have this complaint, first check to determine if you have the late style TRS.
If it is correct, try removing the switch. If you?re now able to get Park, there?s a good chance the Neutral Safety Back-Up Insulator (see figure 3) is worn.
The new style TRS applies more pressure to the plastic insulator then the previous Neutral Safety Back-Up switch and can wear to the point that the linkage can?t get past one of the contacts.
To repair the problem the valve body will need to be removed and the insulator replaced.