CIRCUIT DESCRIPTION:
SEM allows the TCM to request torque reduction from the engine controller. By reducing torque, shifts can be made quicker, at a more consistent output torque which reduces clutch temperature and increases clutch life. DTC P2637 sets when the TCM detects one of the following conditions for a minimum of four upshifts (consecutive or nonconsecutive) during one drive cycle:
1. Engine Control Module (ECM) is not responding to SEM torque reduction signal request from the TCM.
2. A non-approved J1939 device is interfering with the SEM torque reduction signal request.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2637 is active, the following conditions occur:
1. The CHECK TRANS light illuminates (non-OBD II strategy).
2. The TCM forces Variable Modulated Main off.
3. The TCM will not allow full throttle 3rd to 4th, 4th to 5th range or 5th to 5th range upshifts.
4. The DTC is stored in the TCM history.

CONDITIONS FOR CLEARING THE DTC:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without the DTC recurring.

DIAGNOSTIC AIDS:
1. Poor engine performance can allow this code to set. Have the OEM inspect for possible exhaust manifold pressure sensor concern or other engine related subsystems.
2. It will be necessary to drive the vehicle with heavy to moderate throttle settings for at least four upshift cycles in order to set DTC P2637.
3. If DTC P0614 is set in combination with DTCs P2637 and/or DTC P2641, engine control software is not correct. Verify the proper software is installed.