P1740

Schematic:

Circuit Description with 4L30-E Automatic Transmission
The Transmission Control Module (TCM) sends a signal to the Engine Control Module (ECM) requesting reduced engine torque during shift events in order to improve shift feel. The ECM reduces engine torque by retarding the spark timing in response to the TCM request.

This TCM request (signal) is sent to the ECM through a communication network called the controller area network (CAN). Circuits XR888 and XY888 are used to communicate CAN data between the ECM and TCM. When the TCM detects the request for torque reduction has failed, then DTC P1740 will set. DTC P1740 is a type C DTC.

CONDITION FOR RUNNING THE DTC
The ignition switch is in the RUN position.

CONDITION FOR SETTING THE DTC
Request for engine torque reduction has failed.

ACTION TAKEN WHEN THE DTC SETS
^ The TCM flashes the sport mode lamp.
^ The ECM records the operating conditions in the failure records at the time of the request from the TCM.
^ The TCM memory stores the DTC at the time of the first failure.
^ The TCM will command maximum line pressure.
^ The TCM will freeze shift adapts.
^ The TCM will inhibit torque control.

CONDITIONS FOR CLEARING THE STL/DTC
^ A history DTC clears after forty consecutive warm-up cycles, it no failures are present by this diagnostic or any other emission related diagnostic.
^ The scan tool clears the DTC.
^ The TCM cancels the DTC default mode actions when the ignition switch is OFF long enough in order to power down the TCM.

DIAGNOSTIC AIDS
Drive the vehicle and watch the request for torque reduction to be present when shift events occur.

TEST DESCRIPTION

Diagnostic Chart:

The numbers below refer to the step numbers on the diagnostic table.
2. This step verifies the request for torque reduction in present.
5. This step checks for engine DTCs that would normally set if engine torque conditions were detected.