DTC P0726. Chevrolet Optra

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2006 🢒 Optra - Mexico 🢒 Restraints 🢒 SIR 🢒 DTC P0726

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.

DTCs P0725, P0726 and P0727 are related to the same circuit. These DTCs will not illuminate the HOLD or malfunction indicator lamp (MIL), however, the DTC will be stored in memory.

Information transmits between the TCM and engine control module (ECM) through the controller area network (CAN) line. Information is as follows :

•	Engine malfunction signal

•	Engine speed

•	Engine output torque reduction signal

•	Engine coolant temperature

Conditions for Setting the DTC

•	Gear position is D.

•	The engine speed is greater than 7,000 RPM.

•	System voltage is greater than 8.5 volts.

•	The engine is running

•	CAN transmitting wiring harness shorted or open

•	The TCM or ECM is defective.

•	When turbine speed is more than 1,500 RPM, engine speed is less than 400 RPM.

•	Immediately after the above condition occurs

Action Taken When the DTC Sets

•	No lamp control

•	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.

•	Open lock up clutch

Conditions for Clearing the MIL/DTC

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

•	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.

DTC P0726

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	Install the scan tool. Turn the ignition ON, with the engine OFF. Record then clear the DTCs. Turn the ignition OFF. Observe the engine speed on the scan tool. Is the speed within the specified value?	0-7,000 RPM	Go to Diagnostic Aids	Go to Step 3
3	Turn the ignition OFF. Disconnect the transmission 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 B14 or K14 of the ECM wiring connector. Measure the resistance between terminal A16 of the TCM wiring connector and terminal B30 or K15 of the ECM wiring connector. Is the resistance approximately equal to the specified value?	0 ohms	Go to Step 5	Go to Step 4
4	Repair the malfunctioning terminals, as necessary. Is the action complete?	--	System OK	--
5	Turn the ignition ON, with the engine OFF. Measure the voltage of terminal A8. Measure the voltage of terminal A16. Is the voltage within the specified value?	11-14 V	Go to Step 6	Go to Step 7
6	Repair the short to power. Is the action complete?	--	System OK	--
7	Inspect the Engine Speed on the scan tool. Was the engine speed erratic?	--	Go to Diagnostic Starting Point - Engine Controls for the 1.8L (L79) engine or Diagnostic Starting Point - Engine Controls for the 2.0L (L34 GMDAT) engine.	Go to Step 8
8	Replace the TCM. Refer to Transmission Control Module Replacement . Turn the ignition OFF. Turn the ignition ON, with the engine OFF. Verify if DTC P0726 is set. Is The DTC set?	--	Go to Step 9	Go to Step 10
9	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 10	--
10	After the repair, use a scan tool "clear info" function. Road test the vehicle. Review the DTC info. Has the last test failed or is the current DTC displayed?	--	Go to Step 2	System OK