P2638

P2638-TORQUE MANAGEMENT FEEDBACK SIGNAL PERFORMANCE

For a complete wiring diagram Refer to Diagrams/Electrical Electrical Diagrams


Theory of Operation


The Transmission Control Module (TCM) requests torque reductions over the CAN bus during a transmission shift to improve shift quality. The TCM verifies that the PCM / ECM has performed the requested torque reduction by monitoring the response to the request. If the response is not within a specified tolerance, the TCM increments a counter, and if this counter reaches a threshold, the DTC sets.


- When Monitored:

Engine intervention active for at least 20 ms, no engine torque errors, engine torque demand is greater than 0.

- Set Condition:

Torque Reduction acknowledge bit - not set, no shift aborts, the error flag Torque Reduction Acknowledge is not set, Powertrain controller not supporting torque requests.







Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Initial Inspection and Diagnostic Overview



Diagnostic Test


1. CHECK FOR ENGINE DTC PRESENT

With the scan tool, check engine DTCs.

Are there any engine DTCs present?

Yes

- Perform NAG1 TRANSMISSION VERIFICATION TEST. Verification Tests

No

- Go to 2



2. CHECK FOR CAN BUS DTCS

With the scan tool, check for any CAN bus DTCs or a sign of a CAN bus failure.

Are there any CAN bus DTCs present in any module other than the TCM or an overall indication of a CAN bus communication problem?

Yes

- This is an indication of a CAN bus communication problem. Depending on the DTC, either refer to the module reporting the DTC and perform diagnostics for the appropriate symptom.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Verification Tests

No

- Go to 3



3. CHECK IF DTC RESETS

Turn the ignition off to the lock position.

Replace and program the Powertrain Control Module.

With the scan tool, record the Environmental Data and erase Transmission DTCs.


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

Using the Environmental Data recorded earlier, test drive the vehicle while trying to duplicate the conditions in which the DTC originally set.

With the scan tool, read Transmission DTCs.

Did the DTC P2638-TORQUE MANAGEMENT FEEDBACK SIGNAL PERFORMANCE reset?

Yes

- Using the schematics as a guide, check the Transmission Control Module (TCM) pins, terminals, and connectors for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace and program the TCM.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Verification Tests

No

- Test Complete.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Verification Tests