P2638-TORQUE MANAGEMENT FEEDBACK SIGNAL PERFORMANCE

For a complete wiring diagram Refer to Section 8W

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.

Possible Causes

CAN BUS CIRCUIT DTC PRESENT

TRANSMISSION CONTROL MODULE

POWERTRAIN / ENGINE CONTROL MODULE

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)

Diagnostic Test

1. CHECK FOR ENGINE DTC PRESENT

With the scan tool, check engine DTCs.

Are there any engine DTCs present?

Yes

Refer to the 9 - Engine and diagnose the appropriate symptom(s).

Perform NAG1 TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)

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 or (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES - DIAGNOSIS AND TESTING) or refer to 8 - ELECTRICAL - ELECTRONIC CONTROL MODULES and perform the appropriate symptom.
Perform NAG1 TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)

Go To 3

3. CHECK IF DTC RESETS

Turn the ignition off to the lock position.
Replace and program the Powertrain Control Module per the Service Information. Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/POWERTRAIN CONTROL MODULE for the appropriate service procedure.
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 the TCM per the Service Information. (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/TRANSMISSION CONTROL MODULE - REMOVAL)
Perform NAG1 TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)

Test Complete.
Perform NAG1 TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)