GM Service Manual Online
For 1990-2009 cars only

Object Number: 715913  Size: MF
Master Electrical Component List
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

Circuit Description

During shift events, the transmission control module (TCM) sends requests to the engine control module (ECM) to reduce the engine torque in order to improve shift feel. The ECM reduces engine torque by retarding the spark timing in response to the TCM request.

The TCM request is sent to the ECM through a communication network called the controller area network (CAN). Two circuits are used to communicate CAN data between the ECM and TCM. A fault in the CAN will not cause DTC P1740 to set by itself. If a CAN fault occurs, other DTCs will set before DTC P1740.

When the ECM detects that the request for torque reduction has failed, the ECM sends a message to the TCM. When the TCM receives a torque reduction failure message from the ECM, then DTC P1740 will set. DTC P1740 is a type C DTC.

Condition for Running the DTC

The ignition is ON.

Condition for Setting the DTC

The request for engine torque reduction has failed.

Action Taken When the DTC Sets

    • The TCM flashes the sport mode lamp.
    • The TCM memory stores DTC P1740 at the time of the first failure.
    • The ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM records this information as Failure Records.
    • The TCM commands maximum line pressure.
    • The TCM freezes shift adapts from being updated.
    • The TCM inhibits torque control.

Conditions for Clearing the STL/DTC

    • A scan tool can clear the DTC.
    • The TCM clears the DTC from TCM history if the vehicle completes 40  warm-up cycles without a non-emission-related diagnostic fault occurring.
    • The TCM cancels the DTC default 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

The numbers below refer to the step numbers on the diagnostic table.

  1. This step verifies the request for torque reduction is present.

Step

Action

Value(s)

Yes

No

1

Did you perform Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission ?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission

2

  1. Install the Scan Tool .
  2. Turn ON the ignition with the engine OFF.
  3. Important:  Record all Failure Records before clearing the DTC. Using Clear Info erases the Failure Records from the ECM and TCM.

  4. Record the DTC Failure Records.

Did you record any ECM Failure Records?

--

Go to the applicable ECM DTC

Go to Step 3

3

Did you record Failure Records for any of the following DTCs?

    • DTC U2100
    • DTC U2104
    • DTC U2105
    • DTC U2108

--

Go to the applicable CAN Bus DTC

Go to Step 4

4

  1. Clear the DTC.
  2. Turn the ignition OFF for at least 30 seconds.
  3. Road test the vehicle, ensuring that the 1-2,2-3, and 3-4 are completed.
  4. Observe the TCM Torque Red. Req. value on theScan Tool during shifts.

Did DTC P1740 reset?

--

Go to Step 5

Go to Intermittent Conditions in Engine Controls

5

Did any other DTCs set?

--

Go to the applicable DTC

Go to Step 6

6

Replace the ECM. Refer to Engine Control Module Replacement .

Is the action complete?

--

Go to Step 7

--

7

Perform the following operation to verify the repair:

  1. Select DTC on the scan tool.
  2. Select Clear Info.
  3. Road test the vehicle, ensuring that the 1-2,2-3, and 3-4 are completed.
  4. Observe the TCM Torque Red. Req. value on theScan Tool during shifts.

Did DTC P1740 reset?

--

Go to Step 1

System OK