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For 1990-2009 cars only

DTC P0748 4.8L and 6.0L


Object Number: 1587887  Size: MF
Master Electrical Component List
Automatic Transmission Controls Schematics (4.8L and 6.0L)
OBD II Symbol Description Notice
Control Module References

Circuit Description

The pressure control (PC) solenoid valve is a powertrain control module (PCM) controlled device that regulates the transmission line pressure. The PCM compares throttle position (TP) sensor voltage, engine RPM, and other inputs in order to determine the appropriate line pressure for a given load. The PCM regulates line pressure by applying a varying duty cycle to the PC solenoid valve based on the resistance of the solenoid, and the amperage needed to obtain optimum line pressure. The applied amperage varies from 0.1 amps for maximum line pressure to 1.1 amps for minimum line pressure.

If the PCM detects a PC duty cycle that exceeds 95 percent or less than 0.5 percent, 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 greater than 11 volts at -40°C (40°F) TFT or 12 volts at 150°C (302°F) TFT.
    • The engine must be running more than 300 RPM for at least 7 seconds, and not in fuel cut-off.
    • The pressure control solenoid is enabled.

Conditions for Setting the DTC

    • The PC duty cycle exceeds 95 percent or is less than 0.5 percent.
    • All conditions are met for 700 milliseconds (0.7 seconds).

Action Taken When the DTC Sets

    • The PCM does not illuminate the malfunction indicator lamp (MIL).
    • The PCM disables the PC solenoid valve, defaulting the transmission to 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 DTC

    • A scan tool clears the DTC from PCM history.
    • 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 ignition switch is OFF long enough in order to power down the PCM.

Diagnostic Aids

    • Inspect for improperly wired aftermarket equipment.
    • DTC P0748 defaults to an elevated line pressure condition which may result in partial torque converter clutch (TCC) apply. This may produce an idle surge that could stall the engine.

Test Description

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

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

  2. This step tests the PC solenoid valve and the automatic transmission (AT) wiring harness assembly for incorrect resistance.

Step

Action

Value

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

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. With the transmission in PARK, start the engine.
  7. Use the scan tool in order to command 0.1-1.0 amps while observing the PC Sol. Ref. Current and the PC Sol. Actual Current. Refer to Line Pressure .

Does the PC Sol. Actual Current differ from the PC Sol. Ref. Current by more than the specified value?

0.16 amp

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections

3

  1. Turn OFF the ignition.
  2. Disconnect the transmission 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 the PC solenoid valve high control circuit signal and the PC solenoid valve low control circuit signal of the J 44152 . Refer to Automatic Transmission Inline 20-Way Connector End View .

Does the resistance measure within the specified range?

3-7 ohms

Go to Step 5

Go to Step 4

4

Does the resistance measure greater than the specified value?

7 ohms

Go to Step 9

Go to Step 10

5

Measure the resistance from the PC solenoid valve high control circuit signal of the J 44152 to the transmission case. Refer to Automatic Transmission Inline 20-Way Connector End View .

Does the resistance measure greater than the specified value?

250 K ohms

Go to Step 6

Go to Step 11

6

  1. Disconnect the J 44152 from the transmission side of the AT inline 20-way connector.
  2. Connect the transmission AT inline 20-way connector.
  3. Disconnect the PCM connector C2.
  4. Measure the resistance between the PC solenoid valve high control circuit signal and the PC solenoid valve low control circuit signal of the PCM connector.

Does the resistance measure within the specified range?

3-7 ohms

Go to Step 8

Go to Step 7

7

Does the resistance measure greater than the specified value?

7 ohms

Go to Step 12

Go to Step 13

8

Using the DMM and the J 35616 , measure the resistance from the PC solenoid valve high control circuit signal of the PCM connector to ground.

Does the resistance measure greater than the specified value?

250 K ohms

Go to Step 17

Go to Step 14

9

Test the high control circuit and 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 .

Did you find an open condition?

--

Go to Step 16

Go to Step 15

10

Test the high control circuit and the low control circuit of the PC solenoid valve for a shorted together condition between the AT inline 20-way connector and the PC solenoid valve. Refer to Circuit Testing .

Did you find a shorted together condition?

--

Go to Step 16

Go to Step 15

11

Test the high control circuit and 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 .

Did you find a short to ground condition?

--

Go to Step 16

Go to Step 15

12

Test the high control circuit and the low control circuit of the PC solenoid valve for an open between the PCM connector C2 and the AT inline 20-way connector. Refer to Testing for Continuity and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 19

--

13

Test the high control circuit and the low control circuit of the PC solenoid valve for a shorted together condition between the PCM connector C2 and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 19

--

14

Test the high control circuit and the low control circuit of the PC solenoid valve for a short to ground between the PCM connector C2 and the AT inline 20-way connector. Refer to Testing for Short to Ground and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 19

--

15

Replace the PC solenoid valve. Refer to Valve Body and Pressure Switch Replacement .

Did you complete the replacement?

--

Go to Step 19

--

16

Replace the AT wiring harness assembly. Refer to Valve Body and Pressure Switch Replacement .

Did you complete the replacement?

--

Go to Step 19

--

17

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 .

Did you find and correct the condition?

--

Go to Step 19

Go to Step 18

18

Replace the PCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 19

--

19

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Start the engine and ensure that the following condition is met:
  4. The difference between the scan tool PC Sol. Actual Current and the PC Sol. Ref. Current is less than 0.16 amp.

  5. Select Specific DTC.
  6. Enter DTC P0748.

Has the test run and passed?

--

Go to Step 20

Go to Step 2

20

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

System OK