GM Service Manual Online
For 1990-2009 cars only

DTC P0726 Non Eurpoean or N Amer 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 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.

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

The following information transmits between the TCM and the engine control module (ECM) through the controller area network (CAN) line:

    • The engine malfunction signal
    • The engine speed
    • The engine output torque reduction signal
    • The engine coolant temperature

Conditions for Setting the DTC

    • The 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.
    • The TCM or ECM is defective.
    • When turbine speed is more than 1,500 RPM, engine speed is less than 400 RPM.

Action Taken When the DTC Sets

    • The hold lamp will blink.
    • 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 Hold Lamp/DTC

    • The hold lamp will turn OFF when the malfunction has not occurred after 3 ignition cycles.
    • A history DTC will clear after 40 consecutive warm-up cycles without a fault.
    • Using a scan tool can clear history DTCs.

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check - Automatic Transmission?

--

Go to Step 2  2

Go to Diagnostic System Check - Automatic Transmission

2

  1. Install the scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Record, then clear the DTCs.
  4. Turn the ignition OFF.
  5. Observe the engine speed on the scan tool.

Is the speed within the specified values?

0-7,000 RPM

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn the ignition OFF.
  2. Disconnect the transmission control module (TCM) wiring connector and electronic control module (ECM) wiring connector.
  3. Measure the resistance between terminal C2 of the TCM wiring connector and terminal B13 of the ECM wiring connector.

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

  1. Turn ON the ignition, with the engine OFF.
  2. Measure the voltage of terminal C2.

Is the voltage within the specified values?

11-14 V

Go to Step 6

Go to Step 7

6

Repair the short to power.

Did you complete the repair?

--

System OK

--

7

Inspect the engine speed. Refer to Diagnostic System Check - Engine Controls in Engine Controls - 2.0L.

Was a condition found?

--

--

Go to Step 8

8

  1. Replace the TCM. Refer to Transmission Control Module Replacement .
  2. Turn the ignition OFF.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe if DTC P0726 is set.

Is the DTC set?

--

Go to Step 9

Go to Step 10

9

Replace the ECM.

Did you complete the replacement?

--

Go to Step 10

--

10

  1. Clear the DTCs with a scan tool.
  2. Road test the vehicle.
  3. Observe the DTC information with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Step 2

System OK

DTC P0726 Eurpoean and North 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 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.

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

Information transmit between TCM and ECM through the CAN line. 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 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.
    • No engine speed error DTCs P0727, P0725
    • CAN transmitting wiring harness shorted or open.
    • The TCM or ECM is defective.
    • Immediately after the above condition occurs.

Action Taken When the DTC Sets

    • The hold lamp will blink.
    • 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 Hold Lamp/DTC

    • The hold lamp will turn OFF when the malfunction has not occurred after 3 ignition cycles.
    • A history DTC will clear after 40 consecutive warm-up cycles without a fault.
    • Using a scan tool can clear history DTCs.

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check - Automatic Transmission?

--

Go to Step 2  2

Go to Diagnostic System Check - Automatic Transmission

2

  1. Install the scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Record, then clear the DTCs.
  4. Turn the ignition OFF.
  5. Observe the engine speed on the scan tool.

Is the speed within the specified range?

0-7,000 RPM

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn the ignition OFF.
  2. Disconnect the transmission control module (TCM) wiring connector and electronic control module (ECM) wiring connector.
  3. Measure the resistance between terminal A8 of the TCM wiring connector and terminal K14 in 2.0L or terminal 41 in 2.5L of the ECM wiring connector.
  4. Measure the resistance between terminal A16 of the TCM wiring connector and terminal K15 in 2.0L or terminal 22 for 2.5L of the ECM wiring connector.

Is the resistance equal to 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

  1. Turn ON the ignition, with the engine OFF.
  2. Measure the voltage of terminal A8.
  3. Measure the voltage of terminal A16.

Is the voltage within the specified range?

11-14 V

Go to Step 6

Go to Step 7

6

Repair the short to power.

Did you complete the repair?

--

System OK

--

7

Inspect the engine speed. Refer to Diagnostic System Check - Engine Controls in Engine Controls - 2.0L.

Was a condition found?

--

Go to Diagnostic System Check - Engine Controls in Engine Controls-2.0L or Diagnostic System Check - Engine Controls in Engine Controls-2.5L

Go to Step 8

8

  1. Replace the TCM. Refer to Transmission Control Module Replacement .
  2. Turn the ignition OFF.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe 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 in Engine Controls-2.0L or Engine Control Module Replacement in Engine Controls-2.5L.

Did you complete the replacement?

--

Go to Step 10

--

10

  1. Clear the DTCs with a scan tool.
  2. Road test the vehicle.
  3. Observe the DTC information with a scan tool.

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

--

Go to Step 1

System OK