For 1990-2009 cars

### Circuit Description

The transmission control module (TCM) is an electronic device which monitors inputs to control various transaxle functions, including shift quality and transaxle sensors, switches, and components to process for use within the control program. Based on this input information, the TCM controls various transaxle output functions and devices.

Information is transmitted between the TCM and engine control module (ECM) through the CAN. Information is as follows:

• | Engine malfunction signal

• | Engine speed

• | Engine output torque reduction signal

• | Engine coolant temperature

### Conditions for Setting the DTC

• | System voltage is too high or too low.

• | CAN transmitting wiring harness shortage or open

• | The TCM or ECM is defective.

• | Immediately after the above condition occurs

### Action Taken When the DTC Sets

• | The malfunction indicator lamp (MIL) will illuminate.

• | The TCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Failure Records buffer.

• | Adopt Emergency/Substitute mode and constant 4th gear by hydraulic control.

• | After ignition OFF/ON : 3rd gear by hydraulic control. P, R and N also possible.

### Conditions for Clearing the MIL/DTC

• | The MIL will turn OFF when the malfunction has not occurred after 3 ignition cycles.

• | A history DTC will clear after 40 consecutive warm-up cycles without a fault.

• | Using a scan tool can clear history DTCs.

#### DTC 1671

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Turn the ignition OFF.
2. Disconnect the transmission control module (TCM) wiring connector and the engine control module (ECM) wiring connector.
3. Measure the resistance between terminal A8 of the TCM wiring connector and terminal K14 of the ECM wiring connector.
4. Measure the resistance between terminal A16 of the TCM wiring connector and terminal K15 of the ECM wiring connector.

Is the resistance approximately equal to the specified value?

0 ohms

Go to Step 4

Go to Step 3

3 | Repair the malfunctioning terminals, as necessary. Is the action complete? | -- | System OK | --
4 |

1. Turn the ignition ON, with the engine OFF.
2. Measure the voltage of terminal A8.
3. Measure the voltage of terminal A16.

Is the voltage within the specified value?

11-14 V

Go to Step 5

Go to Step 6

5 | Repair the short to power on the terminals, as necessary. Is the action complete? | -- | System OK | --
6 |

1. Replace the TCM. Refer to Transmission Control Module Replacement .
2. Turn the ignition ON, with the engine OFF.
3. Verify if DTC P1671 is set.

Is The DTC set?

--

Go to Step 7

Go to Step 8

7 | Replace the ECM. Refer to Engine Control Module Replacement for the 1.8L (L79) engine or Engine Control Module Replacement for the 2.0L (L34 GMDAT) engine. Is the action complete? | -- | Go to Step 8 | --
8 |

1. After the repair, use a scan tool "clear info" function.
2. Road test the vehicle.
3. Review the DTC info.

Has the last test failed or is the current DTC displayed?

--

Go to Step 2

System OK