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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2000 🢒 Catera 🢒 DTC 🢒 DTC P1740 Torque Reduction Signal Circuit

Object Number: 647013 Size: MF
Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

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, if 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

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

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

    2.

  2. This step checks for engine DTCs that would normally set if engine torque conditions were detected.

DTC P1740 Torque Reduction Signal Circuit

Step

Action

Value(s)

Yes

No

1

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

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Go to Step 2

Go to Transmission On Board Diagnostic (OBD) System Check

2

  1. Install the Scan Tool .
  2. With the engine OFF, turn the ignition switch to the RUN position.

    3. Important:  Before clearing the DTC, use the Scan Tool in order to record the Failure Records. Using the Clear Info function erases the Failure Records from the ECM/TCM.

  3. Record the DTC Failure Records.
  4. Clear the DTC.
  5. Start the engine.
  6. Observe TCM torque reduction required on the Scan Tool .

Does the TCM torque reduction required display NO?

--

Go to Diagnostic Aids

Go to Step 3

3

Does the TCM torque reduction required display YES?

--

Go to Step 4

--

4

Does the engine torque display a high torque value with transmission in D4 and the engine idling?

--

Go to Step 5

--

5

Check for any ECM DTCs.

Are there ECM DTCs present?

--

Go to Step 6

--

6

Go to the appropriate ECM DTC.

Make the necessary repairs. Refer to Engine Controls.

Are the DTC repairs complete?

--

Go to Step 7

--

7

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Start the engine.
  4. Place the transmission in D4 and idle the engine.
  5. Observe TCM torque reduction required on the Scan Tool .

Does the Scan Tool TCM torque reduction required display NO and is DTC P1740 not present?

--

System OK

Go to Step 1