• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

The internal fault detection is handled inside the device. No external circuit diagnosis is involved.

The device runs the program to detect an internal fault when power up is commanded. The only requirements are voltage and ground. This program runs even if the voltage is out of the valid operating range.

The device has detected an internal malfunction.

The device refuses all additional inputs.

• A current DTC clears when the malfunction is no longer present.
• A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.
• P1787 — Shift vehicle into each range (P, R, N, and D) for 5 seconds.

• This DTC may be stored as a history DTC without affecting the operation of the device.
• If stored only as a history DTC and not retrieved as a current DTC, do not replace the device.
• Resolve any current DTC’s that are present relating to the Electronic Transmission Range Selector system prior to replacement of components or programming/setup of module. Faults in any component or module that work together in this system may cause the programming/setup failure.
• Replacement or inspection of Transmission Range Control Module requires rod linkage (if equipped) to be adjusted. If rod linkage is not properly adjusted, programming and setup procedure may fail and DTCs may set. Check Transmission Range Control Module rod linkage adjustment prior to replacing the Transmission Range Control Module. Something as simple as loosening the Transmission Range Control Module mounting bolts can cause the module to be out of adjustment.

Electronic Transmission Range Selector Schematics

Master Electrical Component List

Electronic Transmission Range Selector Description

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Control Module References for scan tool information

1. Verify all other Transmission related faults are not present.
• If Transmission related faults are present

  Refer to Diagnostic Trouble Code (DTC) List - Vehicle

• If Transmission related faults are not present
2. Verify K173 Transmission Range Control Module is mounted securely and if it has a linkage ensure the linkage from Transmission Range Control Module to Transmission is adjusted properly with no excessive play.
• If play is found in the mounting of the K173 Transmission Range Control Module or linkage

  Resolve issue and perform K173 Transmission Range Control Module learn procedure.

• If no play is found in the mounting of the K173 Transmission Range Control Module or linkage
3. Verify data parameter Internal Mode Switch changes appropriately when shifting through all gears.
• If not changing appropriately

  Replace the Internal Mode Switch

• If changing appropriately
4. Check for updated software in K173 Transmission Range Control Module.
• If software is not current

  Perform the programming and learn procedure for the K173 Transmission Range Control Module.

• If software is up to date
5. Check for updated software in K20 Engine Control Module.
• If software is not current

  Perform the programming for the K20 Engine Control Module.

• If software is up to date
6. Replace the K20 Engine Control Module
7. Verify above mentioned DTC’s are not set.
• If above mentioned DTC’s are set

  Replace the K173 Transmission Range Control Module

• If above mentioned DTC’s are not set
8. All OK.

• Perform the Diagnostic Repair Verification after completing the repair.
• Control Module References for device replacement, programming and setup