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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2006 🢒 STS 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 DTC P0748

Circuit Description

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

If the TCM detects a continuous open or short to ground in the PC solenoid 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 ignition is ON.

Conditions for Setting the DTC

The PC solenoid valve feedback circuit indicates a continuous open or short to ground for 1.2 seconds or greater.

Action Taken When the DTC Sets
    • The TCM does not request the ECM to illuminate the malfunction indicator lamp (MIL).
    • SERVICE VEHICLE SOON displays on the driver information center (DIC).
    • The TCM commands maximum line pressure.
    • The TCM freezes transmission adaptive functions.
    • The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as a Failure Record.
    • The TCM stores DTC P0748 in TCM history.

Conditions for Clearing the DIC/DTC
    • The TCM clears the DIC when the condition no longer exists.
    • A scan tool can clear the DTC.
    • The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without a non emission related diagnostic fault occurring.
    • The TCM cancels the DTC default actions when the ignition is OFF long enough in order to power down the TCM.

Test Description

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

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

    2.

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

Step

Action

Value(s)

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 ECM and the TCM Failure Records. Using the Clear Info function erases the Failure Records from the ECM and TCM.
       • Using the Clear Info function erases stored DTCs in both the ECM and TCM.

  3. Record the DTC Failure Records.
  4. Clear the DTC.
  5. Start the engine.
  6. Using the scan tool, increase and decrease the PC solenoid amperage.
  7. 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 Testing for Intermittent Conditions and Poor Connections

3

  1. Turn OFF the ignition.
  2. Disconnect the AT inline 20-way connector. Additional DTCs may set.
  3. Install the J 45681 jumper harness 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 and the PC solenoid valve low control circuit of the J 45681 .

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

Is the resistance within the specified range?

3.5-5.5 Ω

Go to Step 7

Go to Step 4

4

Is the resistance greater than the specified value?

5.5 Ω

Go to Step 5

Go to Step 6

5
  1. Test the high control circuit of the PC solenoid 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 for an open between the AT inline 20-way connector and the PC solenoid valve.

Refer to Testing for Continuity .

Did you find a condition?

--

Go to Step 18

Go to Step 19

6

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

Refer to Circuit Testing .

Did you find the condition?

--

Go to Step 18

Go to Step 19

7

Measure the resistance from PC solenoid valve high control circuit of the jumper harness to ground.

Is the resistance less than the specified value?

10 Ω

Go to Step 8

Go to Step 9

8
  1. Test the high control circuit of the PC solenoid for a short to ground between the AT inline 20-way connector and the PC solenoid.
  2. Test the low control circuit of the PC solenoid for a short to ground between the AT inline 20-way connector and the PC solenoid.

Refer to Testing for Short to Ground .

Did you find a condition?

--

Go to Step 18

Go to Step 19

9

Measure the resistance between the PC solenoid valve high control circuit and all other terminals, except the low control circuit, of the J 45681 . Refer to Automatic Transmission Inline 20-Way Connector End View .

Is the resistance between the PC solenoid valve high control circuit and any other terminal, except the low control circuit, less than the specified value?

100 Ω

Go to Step 18

Go to Step 10

10
  1. Disconnect the J 45681 from the transmission side of the AT inline 20-way connector.
  2. Install the J 45681 on the TCM side of the AT inline 20-way connector.
  3. Disconnect the TCM. Additional DTCs may set.
  4. Using the DMM and the J 35616 , measure the resistance from the PC solenoid valve low control circuit of the J 45681 to ground.

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

Is the resistance less than the specified value?

10 Ω

Go to Step 11

Go to Step 12

11

Test the low control circuit of the PC solenoid for a short to ground between the TCM connector 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 21

--

12

Using the DMM and the J 35616 , measure the resistance of the PC solenoid valve low control circuit between the J 45681 and the TCM connector. Refer to Automatic Transmission Inline 20-Way Connector End View .

Is the resistance less than the specified value?

10 Ω

Go to Step 14

Go to Step 13

13

Test the low control circuit of the PC solenoid for an open between the TCM connector 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 21

--

14

Using the DMM and the J 35616 , measure the resistance from the PC solenoid valve high control circuit of the J 45681 to ground.

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

Is the resistance less than the specified value?

10 Ω

Go to Step 15

Go to Step 16

15

Test the high control circuit of the PC solenoid for a short to ground between the TCM connector 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 21

--

16

Using the DMM and the J 35616 , measure the resistance of the PC solenoid valve high control circuit between the J 45681 and the TCM connector. Refer to Automatic Transmission Inline 20-Way Connector End View .

Is the resistance less than the specified value?

10 Ω

Go to Step 20

Go to Step 17

17

Test the high control circuit of the PC solenoid for an open between the TCM connector 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 21

--

18

Replace the automatic transmission wiring harness. Refer to Transmission Internal Electrical Harness Replacement .

Is the action complete?

--

Go to Step 21

--

19

Replace the PC solenoid. Refer to Pressure Control Solenoid Valve Replacement .

Is the action complete?

--

Go to Step 21

--

20

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

Is the action complete?

--

Go to Step 21

--

21

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 11 volts.
  4. Select Specific DTC.
  5. Enter DTC P0748.

Has the test run and passed?

--

Go to Step 22

Go to Step 2

22

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