DTC P1791. Chevrolet Epica 2005

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2005 🢒 Epica 🢒 Transmission/Transaxle 🢒 Automatic Transmission - ZF 4HP 16 🢒 DTC P1791

DTC P1791 Non Europe or N American Emissions

Circuit Description

The transaxle control module (TCM) is an electronic device which monitors inputs to control various transaxle functions, including shift quality and transaxle senors, 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 theDiagnostic System Check - Automatic Transmission?	--	Go to Step 2	Go to Diagnostic System Check - Automatic Transmission
2	Install the scan tool. Turn ON the ignition, with the engine OFF. Observe the throttle position value on the scan tool. Is the speed within the specified values?	0-100%	Go to Diagnostic Aids	Go to Step 3
3	Turn the ignition LOCK. Disconnect the transaxle control module (TCM) wiring connector and the engine control module (ECM) wiring connector. Measure the resistance between terminal C10 of the TCM wiring connector, and terminal A9 of the ECM wiring connector. Is the resistance within the specified values?	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	Turn ON the ignition, with the engine OFF. Measure the voltage of terminal C10. Is the voltage within the specified values?	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-2.0L. Was a condition found?	--	Verify Repair	Go to Step 8
8	Replace the TCM. Refer to Transmission Control Module Replacement . Turn the ignition to LOCK. Turn ON the ignition, with the engine OFF. Ensure that DTC P1791 is set. 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-2.0L. Did you complete the replacement?	--	Go to Step 10	--
10	Clear the DTCs with a scan tool. Road test the vehicle. Observe the DTC information with a scan tool. Are there any DTCs that have not been diagnosed?	--	Go to Step 2	System OK

DTC P1791 North American Emissions

Circuit Description

The following information transmits between the TCM and the engine control module (ECM) through the CAN. 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	Go to Diagnostic System Check - Automatic Transmission
2	Install the scan tool. Turn ON the ignition, with the engine OFF. Observe the throttle position value on the scan tool. Is the speed within the specified values?	0-100%	Go to Diagnostic Aids	Go to Step 3
3	Turn the ignition OFF. Disconnect the transaxle control module (TCM) wiring connector and the engine control module (ECM) wiring connector. Measure the resistance between terminal A8 of the TCM wiring connector, and terminal 41 of the ECM wiring connector. Measure the resistance between terminal A16 of the TCM wiring connector and terminal 22 of the ECM wiring connector. Is the resistance within the specified values?	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	Turn ON the ignition, with the engine OFF. Measure the voltage of terminal A8. Measure the voltage of terminal A16. Is the voltage within the specified values?	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	Replace the TCM. Refer to Transmission Control Module Replacement . Turn the ignition OFF. Turn ON the ignition, with the engine OFF. Ensure that DTC P1791 is set. 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-2.5L. Did you complete the replacement?	--	Go to Step 9	--
9	After the repair, use a scan tool clear info function and road test the vehicle. Review the DTC info. Are there any DTCs that have not been diagnosed?	--	Go to Step 1	System OK