Ok well then the PNP switch has failed, and need to be replaced.
Here is a bulletin on this condition, you described exactly.
Some customers may comment on one or more of the following conditions.
|• ||The PRNDL display is flashing.|
|• ||The engine will not start.|
|• ||The "Service Engine Soon" Indicator lamp is illuminated.|
|• ||The transmission does not shift properly.|
|• ||The vehicle will not move, transmission will not engage.|
Moisture contamination within the Park Neutral Position (PNP) Switch may cause this condition. This is sometimes referred to as the Neutral Start Back-up (NSBU) Switch. On a left turn, water spray from the left front tire is directed directly at this switch. Proper installation of the "Front Shield" and "Rear Shield" are essential for proper repairs.
Blank PRNDL Display
A blank PRNDL display may indicate a condition with the PNP switch and/or one or more of the four signal circuits from the PNP to the TCM.
- Pin A, Circuit 771 (BLK/WHT)
- Pin B, Circuit 773 (GRA)
- Pin C, Circuit 776 (WHT)
- Pin D, Circuit 772 (YEL)
Or, a blank PRNDL display may also occur if an out of line condition exists with the Serial Data Circuit (CKT 2470, yellow wire) from the TCM to Splice Pack 205.
- Connect the Tech 2® to the vehicle.
- Power up the Tech 2®.
- Does the Tech 2® communicate with the TCM? If not, inspect the serial data circuit, CKT 2470 (Yellow wire), between the TCM and Splice Pack 205. Specifically inspect connector C106, a five terminal connector located below the left side underhood bussed electrical center, directly beneath the red battery cable terminal connection. Perform a mating terminal pull test on all of the terminals in this connector. Repair as required.
- Observe the Gear Selected screen on the scan tool. The following values should be shown on the Tech 2® display and the vehicle's instrument panel cluster (if equipped with the I/P display).
|• ||"8" (shifter should be in the Park position)|
|• ||"7" (shifter should be in the Reverse position)|
|• ||"5" (shifter should be in the Drive position)|
|• ||"3" (shifter should be in the Third gear position)|
|• ||"2" (shifter should be in the Second gear position)|
|• ||"1" (shifter should be in the First gear position)|
|• ||"0" (shifter should be in the Neutral Position)|
If the Gear Selected display does not match the shifter position in the vehicle, diagnose using one of the following methods.
|• ||Obtain a new PNP switch kit, P/N 29540479, from the Parts Department.|
|1. ||Disconnect the wiring connector from the original transmission mounted PNP switch.|
|2. ||Connect the new switch to the wiring connector.|
|3. ||Return to Step #4 above and observe the display as you rotate the switch. If all positions indicate properly, refer to the Correction section below.|
|• ||Use the DTC P0708 diagnostic chart in Service Information (SI) under Transmission/Transaxle/Automatic Transmission - Allison. Reference SI Document ID #769549 for the wiring schematic for this symptom.|
The PNP switch, as referenced in SI, is known as the NSBU switch in the Parts information. It is now serviced with a Park Neutral Position Switch Kit, P/N 29540479.
Disconnect the wiring harness from the PNP switch. Disconnect the shift linkage/cable from the shift lever at the transmission. With a wrench keeping the shift lever from rotating, remove the nut from the end of the selector shaft. Use a file to remove any burrs or raised metal where the selector lever was seated against the shoulder of the selector shaft.
Important: If the old PNP switch will not slide from the selector shaft without the effort, the selector shaft may need to be filed to remove flaring on the end of the selector shaft. This is important, installing the new switch onto a selector shaft that has damage will cause damage to the new PNP switch. Remove the two bolts that attach the PNP switch and remove the switch by sliding it outward over the selector shaft. Make sure the selector shaft is in the N (neutral) position (using a wrench on the selector shaft flats, rotate the shaft to its furthest clockwise position and then rotate counterclockwise two detents).
Important: If the new PNP switch will not slide onto the selector shaft easily, the selector shaft may need to be filed to remove flaring on the end of the selector shaft. This is important, installing the new switch onto a selector shaft that has damage will cause damage to the new PNP switch. Slide the new PNP switch over the selector shaft with the neutral assurance bracket 920 facing outward and maintaining the correct PNP switch orientation to the selector shaft. Install and hand tighten the two PNP switch attaching bolts so that the PNP switch and bracket may be rotated within the adjusting slots with some effort. While holding the neutral assurance bracket in engagement with the PNP switch, tighten the two bolts that attach the PNP switch to the transmission case.
Tighten the bolts to 27 N·m (20 lb ft).
Important: Installation of the front shield and rear shields are important. Without proper installation of the shield, a return repair is probable. Follow all directions as listed on the installation instructions sheet included in the Switch kit, P/N 29540479. Fit the new shield onto the PNP switch so that it fits securely against the switch. Make sure this is done before reinstalling the shift lever.
Reinstall the shift lever. With a wrench keeping the shift lever from rotating, install the nut on the end of the selector shaft.
Tighten. Connect the wiring harness connectors to the PNP switch. Attach the selector cable to the lever. Check and adjust if needed.
Tighten the nut to 24 N·m (18 lb ft).
Switch kit, Park Neutral Position