P2638 Torque management feedback signal performance

P2638 code - The transmission control modul (TCM) request reductions over the CAN bus during a transmission shift to improve shift quality. The TCM verifies that the powertrain control module (PCM) has performed the request 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 this dtc the Engine intervention active for at least 20 ms, no engine torque errors, engine torque demand is greater than 0. Set condition this DTC the Torque reduction acknowledge bit not set, no shift aborts, the error flag torque reduction acknowledge is not set, powertrain controller not supporting torque request.

Possible causes P2638 code:

- CAN BUS circuit dtc present 

- Transmission control module (TCM) 

- Powertrain control module (PCM)

Diagnostic test P2638 code

Step 1. Check for engine DTC present

With the scan tool, check engine DTCs.

Are there any engine DTCs present ?

Yes, refer to  Transmission control Module (TCM) Diagnosis and testing and perform the appropriate diagnostic procedure. Perform NAG1 Transmission Verification Test.

No, go to step 2.

Step 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 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 commnication problem. Depending on the DTC, refer to DTC based diagnostics and non DTC based diagnostic procedures and other possible causes. Perform NAG1 Transmission Verification Test.

No, go to step 3.

Step 3. Check if DTC resets

Turn the ignition off to the lock position. Replace and program the powertrain control module in accordance with the service information. 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) terminals for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace the TCM in accordance with the service information. Perform NAG1 Transmission Verification Test.

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