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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2009 🢒 Aveo 🢒 DTC 🢒 DTC P1791

DTC P1791 European and North American Emissions

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1791 Malfunction of Throttle Position Signal

Conditions for Setting the DTC
    • The transmission control module (TCM) detects that malfunction of throttle position signal for 2 seconds continuously.
    • No DTCs U2105, P1705

Action Taken When the DTC Sets
    • The TCM will request the illumination of the MIL lamp and store the DTC when the TCM detects a failure on the 1st ignition cycle.
    • The TCM judges the throttle opening is 0 percent for shift point control.
    • The TCM judges the throttle opening is 100 percent for line pressure control.
    • No lock-up
    • No 4th gear
    • No self-learning control
    • No timing solenoid control for N-D

Conditions for Clearing the DTC
    • The TCM turns off the MIL lamp when no further failures are detected on the next ignition cycles.
    • The scan tool can clear the DTC from the TCM history.
    • The TCM clears the DTC from the TCM history memory after 40 consecutive ignition cycles without fault.

Cause for Failure
    • Wiring harness or connector between engine control module (ECM) and TCM
    • The ECM
    • The TCM

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Automatic Transmission?

--

Go to Step 2

Go to Diagnostic System Check - Automatic Transmission

2
  1. Turn OFF the ignition.
  2. Install the scan tool.
  3. With the engine OFF, turn the ignition switch to the ON position.
  4. Select Store Freeze Frame/Failure Records from the Diagnostic Trouble Codes Information menu.
  5. Store Freeze Frame/Failure Records.
  6. Select Clear DTC Information from the Diagnostic Trouble Codes Information menu.
  7. Clear DTC Information.
  8. Perform 1 vehicle drive cycle.

Is the MIL lamp ON?

--

Go to Step 3

Go to Step 7

3
  1. Select Request DTC by Status from the Diagnostic Trouble Codes Information menu.
  2. Request DTC by Status.

Is DTC P1791 displayed?

--

Go to Step 4

Go to Step 7

4
  1. Turn OFF the ignition.
  2. Disconnect the transmission control module (TCM) wiring connector and engine control module (ECM) wiring connector.
  3. Measure the resistance between terminal A17 of the TCM wiring connector and terminal K14, or B14, or 88 of the ECM wiring connector.
  4. Measure the resistance between terminal A7 of the TCM wiring connector and terminal K15, or B30, or 57 of the ECM wiring connector.

Is the resistance within the specified values?

0 Ω

Go to Step 5

Go to Step 6

5
  1. Turn ON the ignition.
  2. Measure the voltage of terminal A17.
  3. Measure the voltage of terminal A7.

Is the voltage within the specified range?

11-14 V

Go to Step 6

Go to Step 8

6

Repair the malfunctioning terminals as necessary.

Did you complete the repair?

--

System OK

--

7

Repair the temporary connection failure of the connector.

Did you complete the repair?

--

System OK

--

8
  1. Replace the TCM. Refer to Transmission Control Module Replacement.
  2. Turn OFF the ignition.
  3. Turn ON the ignition.
  4. Verify if DTC P1791 is set.

Is the DTC set?

--

Go to Step 8

Go to Step 9

9

Replace the ECM. Refer to Control Module References.

Did you complete the replacement?

--

Go to Step 9

--

10
  1. After the repair, use a scan tool clear info function and road test the vehicle.
  2. Review the DTC info.

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

--

Go to Step 1

System OK

DTC P1791 Non European and N. American Emission

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1791 Malfunction of Throttle Position Signal

Conditions for Setting the DTC
    • The transmission control module (TCM) detects that malfunction of throttle position signal for 2 seconds continuously.
    • No DTCs U2105, P1705

Action Taken When the DTC Sets
    • The TCM will request the illumination of the hold lamp and store the DTC when the TCM detects a failure on the 1st ignition cycle.
    • The TCM judges the throttle opening is 0 percent for shift point control.
    • The TCM judges the throttle opening is 100 percent for line pressure control.
    • No lock-up
    • No 4th gear
    • No self-learning control
    • No timing solenoid control for N-D

Conditions for Clearing the DTC
    • The TCM turns off the hold lamp when no further failures are detected on the next ignition cycles.
    • The scan tool can clear the DTC from the TCM history.
    • The TCM clears the DTC from the TCM history memory after 40 consecutive ignition cycles without fault.

Cause for Failure
    • Wiring harness or connector between engine control module (ECM) and TCM
    • The ECM
    • The TCM

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Automatic Transmission?

--

Go to Step 2

Go to Diagnostic System Check - Automatic Transmission

2
  1. Turn OFF the ignition.
  2. Install the scan tool.
  3. With the engine OFF, turn the ignition switch to the ON position.
  4. Select Store Freeze Frame/Failure Records from the Diagnostic Trouble Codes Information menu.
  5. Store Freeze Frame/Failure Records.
  6. Select Clear DTC Information from the Diagnostic Trouble Codes Information menu.
  7. Clear DTC Information.
  8. Perform 1 vehicle drive cycle.

Is the hold lamp ON?

--

Go to Step 3

Go to Step 7

3
  1. Select Request DTC by Status from the Diagnostic Trouble Codes Information menu.
  2. Request DTC by Status.

Is DTC P1791 displayed?

--

Go to Step 4

Go to Step 7

4
  1. Turn OFF the ignition.
  2. Disconnect the transmission control module (TCM) wiring connector and engine control module (ECM) wiring connector.
  3. Measure the resistance between terminal A17 of the TCM wiring connector and terminal K14, or B14, or 88 of the ECM wiring connector.
  4. Measure the resistance between terminal A7 of the TCM wiring connector and terminal K15, or B30, or 57 of the ECM wiring connector.

Is the resistance within the specified range?

0 Ω

Go to Step 5

Go to Step 6

5
  1. Turn ON the ignition.
  2. Measure the voltage of terminal A17.
  3. Measure the voltage of terminal A7.

Is the voltage within the specified values?

11-14 V

Go to Step 6

Go to Step 8

6

Repair the malfunctioning terminals as necessary.

Did you complete the repair?

--

System OK

--

7

Repair the temporary connection failure of the connector.

Did you complete the repair?

--

System OK

--

8
  1. Replace the TCM. Refer to Transmission Control Module Replacement .
  2. Turn OFF the ignition.
  3. Turn ON the ignition.
  4. Verify if DTC P1791 is set.

Is the DTC set?

--

Go to Step 9

Go to Step 10

9

Replace the ECM. Refer to Control Module References .

Did you complete the replacement?

--

Go to Step 10

--

10
  1. After the repair, use a scan tool clear info function and road test the vehicle.
  2. Review the DTC info.

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

--

Go to Step 1

System OK