DTC P1791 Non-European or N. American Emissions
Circuit Description
The transmission control module (TCM) is an electronic device that monitors inputs to control various transaxle function, including shift quality and transaxle sensors, switches, and components to process for use within its control program. Based on this input information, the TCM controls various transaxle output functions and devices.
The following information transmits between the TCM and the engine control module (ECM) through the DISCREET line:
| • | The engine speed |
| • | The engine output torque reduction signal |
Conditions for Setting the DTC
| • | The system voltage is too high or too low. |
| • | The DISCREET transmitting wiring harness is shorted or open. |
| • | The TCM or ECM is defective. |
Action Taken When the DTC Sets
| • | No lamp control is required, but diagnostic information should be stored immediately when the malfunction is detected. |
| • | Adjustable value, calculated over the substitute map throttle position, such as engine speed or engine torque |
Conditions for Clearing the DTC
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | Using a scan tool can clear history DTCs. |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Automatic Transmission? | -- | Go to Step 2 | |
2 |
Is the speed within the specified range? | 0-100% | Go to Diagnostic Aids | Go to Step 3 |
3 |
Is the resistance within the specified value? | 0 ohms | Go to Step 5 | Go to Step 4 |
4 | Repair the malfunctioning terminals, as necessary. Did you complete the repair? | -- | System OK | -- |
5 |
Is the voltage within the specified range? | 11-14 V | Go to Step 6 | Go to Step 7 |
6 | Repair the malfunctioning terminals, as necessary. Did you complete the repair? | -- | System OK | -- |
7 | Inspect the throttle position. Refer to Diagnostic System Check - Engine Controls in Engine Controls - 1.8L. Was a condition found? | -- | Go to Throttle Position Sensor Replacement in Engine Controls - 1.8L | Go to Step 8 |
8 |
Is DTC P1791 set? | -- | Go to Step 9 | Go to Step 10 |
9 | Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls - 1.8L. Did you complete the replacement? | -- | Go to Step 10 | -- |
10 |
Are there any DTCs that have not been diagnosed? | -- | Go to Step 2 | System OK |
DTC P1791 North American Emissions
Circuit Description
The transmission control module (TCM) is an electronic device that monitors inputs to control various transaxle functions, including shift quality and transaxle sensors, switches, and components to process for use within its control program. Based on this input information, the TCM controls various transaxle output functions and devices.
The following information transmits between the TCM and the engine control module (ECM) through the controller area network (CAN). The information is as follows:
| • | The engine malfunction signal |
| • | The engine speed |
| • | The engine output torque reduction signal |
| • | The engine coolant temperature |
Conditions for Setting the DTC
| • | The system voltage is too high or too low. |
| • | The TCM or ECM is defective. |
Action Taken When the DTC Sets
| • | No lamp control is required, but diagnostic information should be stored immediately when the malfunction is detected. |
| • | Adjustable value, calculated over the substitute map throttle position, such as engine speed or engine torque |
Conditions for Clearing the DTC
Using a scan tool can clear history DTCs.
Diagnostic Aids
| • | Inspect the poor wiring harness connection for TCM connectors and transaxle wiring connectors. |
| • | Inspect the improperly formed or damaged terminals. |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Automatic Transmission? | -- | Go to Step 2 | |
2 |
Is the speed within the specified range? | 0-100% | Go to Diagnostic Aids | Go to Step 3 |
3 |
Is the resistance within the specified value? | 0 ohms | Go to Step 5 | Go to Step 4 |
4 | Repair the malfunctioning terminals, as necessary. Did you complete the repair? | -- | System OK | -- |
5 |
Is the voltage within the specified range? | 11-14 V | Go to Step 6 | Go to Step 7 |
6 | Repair the malfunctioning terminals, as necessary. Did you complete the repair? | -- | System OK | -- |
7 |
Is DTC P1791 set? | -- | Go to Step 8 | Go to Step 9 |
8 | Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls - 2.0L. Did you complete the replacement? | -- | Go to Step 9 | -- |
9 |
Are there any DTCs that have not been diagnosed? | -- | Go to Step 2 | System OK |
