GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2006 🢒 Optra - Mexico 🢒 Restraints 🢒 SIR 🢒 DTC P1791

DTC P1791 Non European Emissions

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1791 Throttle/Pedal Position Signal

Conditions for Setting the DTC
    • Transmission control module (TCM) detects that malfunction of throttle position signal for 2 seconds continuously
    • No DTC U2105

Action Taken When the DTC Sets
    • TCM will request the illumination of the hold lamp and store the DTC when the TCM detects a failure on the 1st ignition cycle
    • TCM judges the throttle opening is 0 percent for shift point control
    • 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
    • ECM
    • TCM

Step

Action

Values

Yes

No

1
  1. Turn OFF the ignition.
  2. Install the scan tool.
  3. Turn ON the ignition, with the engine OFF.
  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 one vehicle drive cycle.

Is the hold lamp ON?

--

Go to Step 2

Go to Step 6

2
  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 3

Go to Step 6

3
  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 88 of the ECM wiring connector.
  4. Measure the resistance between terminal A7 of the TCM wiring connector and terminal 57 of the ECM wiring connector.

Is the resistance equal to the specified value?

0 ohms

Go to Step 4

Go to Step 5

4
  1. Turn ON the ignition, with the engine OFF.
  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 5

Go to Step 7

5

Repair the malfunctioning terminals as necessary.

Did you complete the repair?

--

System OK

--

6

Repair the temporary connection failure of the connector. Refer to Wiring Harness and Connector Inspection Diagnosis .

Did you complete the repair?

--

System OK

--

7
  1. Replace the TCM. Refer to Transmission Control Module Replacement .
  2. Turn OFF the ignition.
  3. Turn ON the ignition.
  4. Inspect for DTC P1791.

Is the DTC set?

--

Go to Step 8

Go to Step 9

8

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.

Did you complete the replacement?

--

Go to Step 9

--

9
  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 European Emissions

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1791 Throttle/Pedal Position Signal

Conditions for Setting the DTC
    • Transmission control module (TCM) detects that malfunction of throttle position signal for 2 seconds continuously
    • No DTC U2105

Action Taken When the DTC Sets
    • TCM will request the illumination of the malfunction indicator lamp (MIL) and store the DTC when the TCM detects a failure on the 1st ignition cycle
    • TCM judges the throttle opening is 0 percent for shift point control
    • 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 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
    • ECM
    • TCM

Step

Action

Values

Yes

No

1
  1. Turn OFF the ignition.
  2. Install the scan tool.
  3. Turn ON the ignition, with the engine OFF.
  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 one vehicle drive cycle.

Is the malfunction indicator lamp (MIL) ON?

--

Go to Step 2

Go to Step 6

2
  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 3

Go to Step 6

3
  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  88 of the ECM wiring connector.
  4. Measure the resistance between terminal A7 of the TCM wiring connector and terminal 57 of the ECM wiring connector.

Is the resistance equal to the specified value?

0 ohms

Go to Step 4

Go to Step 5

4
  1. Turn ON the ignition, with the engine OFF.
  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 5

Go to Step 7

5

Repair the malfunctioning terminals as necessary.

Did you complete the repair?

--

System OK

--

6

Repair the temporary connection failure of the connector. Refer to Wiring Harness and Connector Inspection Diagnosis .

Did you complete the repair?

--

System OK

--

7
  1. Replace the TCM. Refer to Transmission Control Module Replacement .
  2. Turn OFF the ignition.
  3. Turn ON the ignition.
  4. Inspect for DTC P1791.

Is the DTC set?

--

Go to Step 8

Go to Step 9

8

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.

Did you complete the replacement?

--

Go to Step 9

--

9
  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