For 1990-2009 cars
Automatic Transmission Controls Schematics
Automatic Transmission Components
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The TCM sends a signal to the ECM requesting reduced engine torque during transmission shift events in order to improve shift feel. The ECM reduces engine torque by retarding the spark timing in response to this signal. The Transmission Torque Reduction Request Circuit is pulled up to B+ within the ECM. The TCM induces a signal on the circuit by Pulse Width Modulating the circuit to ground. The signal frequency is constant at approximately 100 Hz. The requested amount of timing retard is sent by varying the duty cycle of this signal.

### Conditions for Running the DTC

Command the Transmission Torque Reduction Request Circuit output on high.

### Conditions for Setting the DTC

The Transmission Torque Reduction Request Circuit output state remains low

### Action Taken When the DTC Sets

• | The TCM illuminates the Service Transmission Lamp (STL) and sends a MIL Request to the ECM on the second consecutive drive trip that the diagnostic runs and fails. The ECM then illuminates the MIL.

• | The ECM records the operating conditions in the Freeze Frame at the time of the MIL Request from the TCM.

• | The transmission operates in the Default Mode.

### Conditions for Clearing the MIL/DTC

• | The TCM turns off the STL as soon as the fault is no longer present.

• | The ECM turns off the MIL after three consecutive drive trips during which the TCM sends no MIL Request.

• | 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 MIL/DTC.

### Diagnostic Aids

Use the Connector Test Adapter Kit J 35616-A for any test that requires probing the TCM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.

Check for the following conditions:

• | Poor connections at the TCM or at the component. Inspect the harness connectors for any backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Engine Electrical, Troubleshooting Procedures, Checking Terminal Contact for proper procedure.

• | Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving any related connectors and any wiring harnesses. A change in the display may help to locate the fault.

### Test Description

The number(s) below refer to the step number(s) on the Diagnostic Table.

1. Check the circuit for the following conditions which may cause an intermittent problem:

• | Poor connections at the ECM or TCM. Inspect the harness connectors for any backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Engine Electrical, Troubleshooting Procedures, Checking Terminal Contact for proper procedure.

• | Misrouted harness. Inspect the harness in order to ensure that the harness is not routed too close to high voltage wires such as spark plug leads, or too close to high current devices such as the alternator, motors, solenoids etc.

• | Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving any related connectors and any wiring harnesses. A change in the display may help in order to locate the fault.

#### DTC P1740 - Transmission Torque Reduction Request Circuit

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Turn off the ignition.
2. Disconnect the TCM.
3. Turn on the ignition with the engine off.
4. Use a DVM J 39200 in order to measure the voltage on the Transmission Torque Reduction Request Circuit at the TCM harness connector.

Does the DVM indicate the specified voltage?

B+

Go to Step 5

Go to Step 3

3 |

1. Turn off the ignition.
2. Disconnect the ECM.
3. Use a DVM J 39200 in order to check the harness for continuity on the Transmission Torque Reduction Request Circuit from the ECM to the TCM.

Is the continuity present?

--

Go to Step 4

Go to Step 6

4 | Use a DVM J 39200 in order to check the continuity between the Transmission Torque Reduction Request Circuit and ground. Is the continuity indicated? | -- | Go to Step 7 | Go to Step 9
5 | With a test light J 34142-B connected to ground, probe the Transmission Torque Reduction Request Circuit at the TCM harness connector. Does the test light illuminate? | -- | Go to Step 8 | Go to Step 11
6 | Repair the open/high resistance request circuit. Is the action complete? | -- | Go to Step 12 | --
7 | Repair the request circuit shorted to ground. Is the action complete? | -- | Go to Step 12 | --
8 | Repair the request circuit shorted to B+. Is the action complete? | -- | Go to Step 12 | --
9 | Check the ECM harness connector for a poor connection or poor terminal tension. Refer to Engine Electrical, Troubleshooting Procedures, Checking Terminal Contact for proper procedure. Was a problem found and corrected? | -- | Go to Step 12 | Go to Step 10
10 | Important: This vehicle is equipped with a Theft Deterrent System which interfaces with the Engine Control Module (ECM). Program the new ECM with the frequency code of the theft deterrent module currently on the vehicle. Replace the ECM. Refer to Engine Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 12

--

11 | Check the TCM harness connector for a poor connection or poor terminal tension. Refer to Engine Electrical, Troubleshooting Procedures, Checking Terminal Contact for proper procedure. Was a problem found and corrected? | -- | Go to Step 12 | Go to Test Description
12 |

1. Clear the DTCs with the scan tool.
2. Turn off the ignition for 15 seconds.
3. Start the engine.
4. Operate the vehicle within the conditions for this diagnostic to run. Refer to Conditions for Running the DTC.
5. Check for any DTCs.

Is DTC P1740 set?

--

Go to Step 2

Go to Step 13

13 | Were there any additional DTCs noted during the Powertrain or Transmission OBD System Check that have not been diagnosed? | -- | Go to the applicable DTC table | Go to Step 14
14 | Does the Transmission now function properly? | -- | System OK | Go to Functional Test