P2640 Possible Causes
- Faulty Engine Control Module (ECM)
- Faulty Transmission Control Module (TCM)
- Engine Control Module (ECM) software update
- Transmission Control Module (TCM) software update
- Engine Control Module (ECM) harness is open or shorted
- Poor electrical connection in Engine Control Module (ECM) circuit
How to Fix Code P2640
Check the “Possible Causes” listed above. Visually inspect the related wiring harness and connectors. Look for damaged components and check for broken, bent, pushed out, or corroded connector pins.
Possible Symptoms
Engine Light On (or Service Engine Soon Warning Light)
P2640 Meaning
To improve shift feel, the Transmission Control Module (TCM) may request that the Engine Control Module (ECM) reduce engine torque during shift events. When such a request is received, the ECM responds by retarding base ignition timing and notifying the TCM that the request was successful. If the ECM is unable to comply with the request, the ECM sends the TCM a message indicating the request failed.
The torque reduction request is sent to the ECM via a communication network called CAN (Controller Area Network). Two circuits are used to communicate CAN data between the ECM and TCM.
A fault in the CAN will not cause the ECM to set Diagnostic Trouble Codes (DTCs). If a CAN fault occurs, other DTCs will be set before this code.
The ECM sets the OBDII code when the TCM receives a torque reduction failure message from the ECM.