GM Service Manual Online
For 1990-2009 cars only

Object Number: 1492406  Size: SF
Master Electrical Component List
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice
Control Module References

Circuit Description

The pressure control (PC) solenoid valve regulates actuator feed fluid passing through the solenoid into torque signal pressure. The powertrain control module (PCM) uses a pulse width modulated signal in order to control the torque signal pressure. The PCM compares various inputs in order to determine the appropriate pressure for a given load. The PCM varies the current to the PC solenoid valve from 0.1 amps, for maximum line pressure to 1.1 amps, for minimum line pressure. An internal current monitor within the PCM provides feedback in order to determine actual PC solenoid valve current draw.

If the PCM detects a continuous open, short to ground or short to voltage in the PC solenoid valve circuit, then DTC P0748 sets. DTC P0748 is a type C DTC.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0748 Pressure Control (PC) Solenoid Control Circuit

Conditions for Running the DTC

    • The system voltage is at least 10.7 volts.
    • The engine speed is 400 RPM or greater.

Conditions for Setting the DTC

The PC solenoid valve feedback circuit detects one of the following conditions for greater than 0.1 second:

    • Continuous open
    • Short to ground
    • Short to voltage

Action Taken When the DTC Sets

    • The PCM does not illuminate the malfunction indicator lamp (MIL).
    • The PCM commands maximum line pressure.
    • The PCM freezes transmission adaptive functions.
    • The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Failure Records.
    • The PCM stores DTC P0748 in PCM history.

Conditions for Clearing the DIC/DTC

    • The PCM clears the DIC when the condition no longer exists.
    • A scan tool can clear the DTC.
    • The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without a non-emission-related diagnostic fault occurring.
    • The PCM cancels the DTC default actions when the fault no longer exists and the DTC passes.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step verifies the ability of the PCM to command the PC solenoid valve.

  2. This step verifies that the automatic transmission wiring harness and the PC solenoid valve have correct resistance.

DTC P0748

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Important: Before clearing the DTC, use the scan tool in order to record the Failure Records. Using the Clear Info function erases the Failure Records from the PCM.

  4. Record the DTC Failure Records.
  5. Clear the DTC.
  6. Start the engine.
  7. Using the scan tool, increase and decrease the PC solenoid valve amperage.
  8. Observe the scan tool display.

Does the PC Sol. Actual Current vary from the PC Sol. Ref. Current by more than the specified amount?

0.05 amps

Go to Step 3

Go to Intermittent Conditions in Engine Controls

3

  1. Turn OFF the ignition.
  2. Disconnect the AT inline 20-way connector. Additional DTCs may set.
  3. Install the J 44152 Jumper Harness (20 pins) on the transmission side of the AT inline 20-way connector.
  4. Using the DMM and the J 35616 GM Terminal Test Kit, measure the resistance between terminals C and D of the J 44152 .
  5. Refer to Automatic Transmission Inline 20-Way Connector End View .

Does the resistance measure within the specified range?

3-7 ohms

Go to Step 7

Go to Step 4

4

Does the resistance measure greater than the specified value?

7 ohms

Go to Step 5

Go to Step 6

5

  1. Test the high control circuit of the PC solenoid valve for an open between the AT inline 20-way connector and the PC solenoid valve.
  2. Test the low control circuit of the PC solenoid valve for an open between the AT inline 20-way connector and the PC solenoid valve.

Refer to Testing for Continuity in Wiring Systems.

Did you find a condition?

--

Go to Step 19

Go to Step 20

6

Test the high control circuit and the low control circuit of the PC solenoid valve for being shorted together between the AT inline 20-way connector and the PC solenoid valve.

Refer to Circuit Testing in Wiring Systems.

Did you find the condition?

--

Go to Step 19

Go to Step 20

7

Measure the resistance from terminal C of the J 44152 to ground.

Refer to Automatic Transmission Inline 20-Way Connector End View .

Does the resistance measure less than the specified value?

250 K ohms

Go to Step 8

Go to Step 9

8

  1. Test the high control circuit of the PC solenoid valve for a short to ground between the AT inline 20-way connector and the PC solenoid valve.
  2. Test the low control circuit of the PC solenoid valve for a short to ground between the AT inline 20-way connector and the PC solenoid valve.

Refer to Testing for Short to Ground in Wiring Systems.

Did you find a condition?

--

Go to Step 19

Go to Step 20

9

Measure the resistance between terminal C and all other terminals, except terminal D, of the J 44152 .

Refer to Automatic Transmission Inline 20-Way Connector End View .

Does the resistance measure less than the specified value?

100 ohms

Go to Step 19

Go to Step 10

10

  1. Disconnect the J 44152 from the transmission side of the AT inline 20-way connector.
  2. Install the J 44152 on the engine side of the AT inline 20-way connector.
  3. Disconnect PCM connector C3. Additional DTCs may set.
  4. Using the DMM and the J 35616 , measure the resistance from terminal D of the J 44152 to ground.

Refer to Automatic Transmission Inline 20-Way Connector End View .

Does the resistance measure less than the specified value?

250 K ohms

Go to Step 11

Go to Step 12

11

Test the low control circuit of the PC solenoid valve for a short to ground between the PCM connector C3 and the AT inline 20-way connector.

Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 22

--

12

Using the DMM and the J 35616 , measure the resistance between terminal D of the J 44152 and terminal 3 of the PCM connector C3.

Refer to Automatic Transmission Inline 20-Way Connector End View .

Does the resistance measure less than the specified value?

10 ohms

Go to Step 14

Go to Step 13

13

Test the low control circuit of the PC solenoid valve for an open between the PCM connector C3 and the AT inline 20-way connector.

Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 22

--

14

Using the DMM and the J 35616 measure the resistance from terminal C of the J 44152 to ground.

Refer to Automatic Transmission Inline 20-Way Connector End View .

Does the resistance measure less than the specified value?

250 K ohms

Go to Step 15

Go to Step 16

15

Test the high control circuit of the PC solenoid valve for a short to ground between the PCM connector C3 and the AT inline 20-way connector.

Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 22

--

16

Using the DMM and the J 35616 measure the resistance between terminal C of the J 44152 and terminal 45 of the PCM connector C3.

Refer to Automatic Transmission Inline 20-Way Connector End View .

Does the resistance measure less than the specified value?

10 ohms

Go to Step 21

Go to Step 17

17

Test the high control circuit of the PC solenoid valve for an open between the PCM connector C3 and the AT inline 20-way connector.

Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 18

18

Test the high control circuit and the low control circuit of the PC solenoid for a short to voltage.

Refer to Testing for a Short to Voltage and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 21

19

Important: The automatic transmission wiring harness consists of 2 separate harnesses, the Automatic Transmission Wiring Harness Assembly and the Automatic Transmission Wiring Extension Harness Assembly. In order to avoid the unnecessary replacement of parts, only replace the Automatic Transmission Wiring Harness Assembly.

Replace the automatic transmission wiring harness.

Refer to Input Speed Sensor and Wiring Harness Removal in the 4T80-E section of the Transmission Unit Repair Manual.

Did you complete the replacement?

--

Go to Step 22

--

20

Replace the PC solenoid valve.

Refer to Control Valve Upper Body Disassemble in the 4T80-E section of the Transmission Unit Repair Manual.

Did you complete the replacement?

--

Go to Step 22

--

21

Replace the PCM.

Refer to Control Module References in Computer/Integrating Systems.

Did you complete the replacement?

--

Go to Step 22

--

22

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle under the following conditions:
  4. • Start and idle the engine.
    • System voltage must be at least 10.7 volts.
  5. Select Specific DTC.
  6. Enter DTC P0748.

Has the test run and passed?

--

Go to Step 23

Go to Step 2

23

With the scan tool, observe the stored information, capture info. and DTC info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK