DIAGNOSTIC RESPONSE:
Inhibit LRTP
CIRCUIT DESCRIPTION:
Lower Range Torque Protection (LRTP) is an Engine Management function that reduces engine torque when transmission input power, input torque, converter torque output, or converter speed ratio exceeds defined limits. These limits typically occur during torque converter mode or operation in lower gears, where stall or drivetrain torque may reach levels above gearbox capacity. The Transmission Control Module (TCM) only activates LRTP when connected with a compatible electronic engine and control system.
This test detects:
If the engine Electronic Control Module (ECM) responds to SAE J1939 transmission torque reduction commands.
For high torque applications, the engine must support the required messages to allow LRTP. For low torque applications, LRTP may or may not be active.
CONDITIONS FOR RUNNING THE DTC:
1. Net engine torque is greater than 500 N·m (369 lb ft).
2. Shift is not in process.
3. This DTC and DTC U0115 not active.
CONDITIONS FOR SETTING THE DTC:
LRTP enabled engines has net engine torque values exceeding LRTP torque limit for more than 5 seconds.
ACTION TAKEN WHEN THE DTC SETS:
1. The CHECK TRANS light illuminates.
2. DTC is stored in the TCM history.
3. Transmission sends default torque limit and/or stop transmission broadcast of SAE J1939/71 ETC1.
4. The TCM freezes shift adapts (DNA).
5. The TCM inhibits TCC engagement.
6. DTCs P0614 and/or P2637 may also be active.
CONDITIONS FOR CLEARING THE DTC:
The TCM will continue attempting to use LRTP, and will self-clear the active DTC if engine response returns to within acceptable criteria.
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:
DTC P2641 may be caused by:
1. Incorrect engine calibration.
2. Incorrect transmission calibration.
3. Engine calibration that does not support all required SAE J1939 LRTP messages.
4. Communication link problem.
5. Vehicle controller (such as a headway controller) preventing transmission control of the engine during the shift process.
6. Defective TCM.
Review applicable information in the OEM Technician’s Library, General Troubleshooting Of Performance Complaints Shift Selector Issues, Control System and Transmission Specifications, and other related information.
