Transmission Control Systems: Testing and Inspection

NAG1 PRE-DIAGNOSTIC TROUBLESHOOTING PROCEDURE

For a complete wiring diagram Consult Diagrams/Electrical

Perform the following pre-diagnostic troubleshooting procedures prior to performing any diagnostic test.

NOTE: Due to different power control configurations, the Transmission Control Relay (if equipped) may be referred to as a PCM relay.

NOTE: Incorrect fluid level, and/or poor fluid condition can be the cause of many transmission problems. Visually inspect the transmission and cooler lines for leakage and repair as necessary and adjust the fluid level.

Always perform diagnostics with a fully charged battery to avoid false symptoms.

1. With the scan tool, read the engine DTCs. Check and repair all engine DTCs prior to performing transmission symptom diagnostic procedures.
2. With the scan tool, read and record all Transmission DTCs. Record the controller software version and variant ID (configuration or level).

NOTE: Check for any Service Information Tune-ups or Technical Service Bulletins (TSB) that may apply.

NOTE: If the TCM detects and stores a DTC, the TCM also stores the vehicles operating conditions under which the DTC originally set. This information is located using a scan tool under Environmental Data. Before erasing any stored DTCs, it is recommended to record all available data to assist in troubleshooting and duplicating the conditions and in which the DTC originally set.

3. Verify the current software level of transmission controller. Various problems are corrected by software upgrades (flash) to the transmission controller.

NOTE: If a TCM software update is performed, all DTC information (Environmental Data) will be lost.

4. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors to all components related to the transmission and shift lever assembly. Clean and repair as necessary.
5. Most DTCs set on start up but some may only set by driving the vehicle. Note the when monitored and set conditions of the reported DTC. If variant DTCs are present, perform their respective test first.
6. Verify the axle ratio and transfer case ratio.

NOTE: The Transfer case ratio must be programmed using the scan tool under the appropriate gateway module (FCM, FDCM, and/or TIPM) even if equipped with AWD or NO transfer case. Validate that the left to right tire sizes on each axle are the same. Do not perform diagnostics using a space-saver spare tire. Invalid tire sizes (right to left) may cause erroneous DTCs to set.

Did any of the above procedures repair the vehicle?

Yes

- Testing is complete.
- Perform NAG1 TRANSMISSION VERIFICATION TEST.Transmission Verification Test

No

- Refer to the identified category and perform the appropriate procedure(s).