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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC MD Steel Tilt (W Model) 🢒 DTC 🢒 DTC P0748 Pressure Control Solenoid Circuit Electrical

Object Number: 362788 Size: MF
Automatic Transmission Components
Automatic Transmission Controls Schematics Gas
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

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 1.9 percent, then DTC P0748 sets. DTC P0748 is a type D DTC.

Conditions for Running the DTC
    • The system voltage is greater than 10.0 volts at -40°C TFT or 12.5 volts at 150°C TFT.
    • The engine must be running more than 475 RPM for at least 7 seconds, and not in fuel cut-off.

Conditions for Setting the DTC
    • The PC duty cycle exceeds 95 percent or is less than 1.9 percent.
    • All conditions are met for 200 milliseconds (0.2 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 shift adapts.
    • 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 consecutive 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 the wiring at the PCM, the transmission connector and all other circuit connecting points for the following conditions:
       - A backed out terminal
       - A damaged terminal
       - Reduced terminal tension
       - A chafed wire
       - A broken wire inside the insulation
       - Moisture intrusion
       - Corrosion
    • When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
    • First diagnose and clear any engine DTCs or TP sensor codes that are present. Then inspect for any transmission DTCs that may have reset.
    • Inspect for improperly wired after-market equipment.

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.

  2. This step tests the PC solenoid valve and the A/T wiring harness assembly for incorrect resistance.

    3.

  3. This step tests the PC solenoid valve and the internal wiring harness for a short to ground.

    4.

  4. When performing this step refer to Product Service Bulletin #9474L80E-07 for PC Solenoid Valve Application.

    5.

  5. This step tests the entire PC solenoid valve circuit up to the PCM for continuity.

    6.

  6. This step tests for a short to ground in CKT 1228 and CKT 1229, of the engine harness.

DTC P0748

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Install the Scan Tool .
  2. With the engine OFF, turn the ignition switch to the RUN position.

    3. Important: Before clearing the DTCs, use the scan tool in order to record the Failure Records. Using the Clear Info function erases the Failure Records from the PCM.

  3. Record the Failure Records.
  4. Clear the DTCs.
  5. With the transmission in PARK, start the engine.
  6. Using the transmission output control function on the scan tool, apply 0.1-1.0 amps while observing the PC Ref. current and the PC Act. current.

Is the PC Act. current reading always within the specified value of the PC Ref. current? (Refer to the Line Pressure specification table.)

0.16 amp

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn the ignition OFF.
  2. Disconnect the transmission 20-way connector (additional DTCs will set).
  3. Install the J 39775 jumper harness on the transmission side of the 20-way connector (Automatic Transmission Connector End View).
  4. Using the J 39200 digital multimeter (DMM) and the J 35616 connector test adapter kit, measure the resistance between terminals C and D.

Is the resistance within the specified range?

3-7Ω

Go to Step 6

Go to Step 4

4
  1. Disconnect the automatic transmission wiring harness assembly at the PC solenoid valve.
  2. Measure the resistance of the PC solenoid valve.

Is the resistance within the specified range?

3-7Ω

Go to Step 5

Go to Step 8

5

Replace the automatic transmission wiring harness assembly.

Refer to Wiring Harness Replacement.

Is the replacement complete?

--

Go to Step 16

--

6

Measure the resistance from terminal C on the jumper harness, to the transmission case.

Is the resistance less than the specified value?

7Ω

Go to Step 7

Go to Step 9

7
  1. Inspect the automatic transmission wiring harness assembly (CKT 1228 RED/BLK and CKT 1229 LT BLU/WHT) for a short to ground condition.

    2. Refer to General Electrical Diagnosis in Wiring Systems.

  2. Replace the harness if necessary.

    3. Refer to Wiring Harness Replacement.

Was a shorted condition found?

--

Go to Step 16

Go to Step 8

8

Replace the PC solenoid valve.

Refer to Pressure Regulator Replacement.

Important: Refer to the Test Description for information on component replacement.

Is the replacement complete?

--

Go to Step 16

--

9

  1. Disconnect the J 39775 from the transmission side of the 20-way connector (Automatic Transmission Connector End View).
  2. Reconnect the transmission 20-way connector.
  3. Disconnect the PCM connector C3.
  4. Measure the resistance between terminals C3-6 and C3-16.

Is the resistance within the specified range?

3-7Ω

Go to Step 10

Go to Step 11

10

  1. Connect the J 39200 DMM to terminal C3-6 and to a good ground.
  2. Measure the resistance.

Is the resistance greater than the specified value?

7Ω

Go to Step 15

Go to Step 14

11

Is the resistance in step 9 greater than the specified value?

7Ω

Go to Step 12

Go to Step 13

12
  1. Inspect CKT 1228 (RED/BLK) for an open.

    2. Refer to General Electrical Diagnosis in Wiring Systems.

  2. Inspect CKT 1229 (LT BLU/WHT) for an open.

    3. Refer to General Electrical Diagnosis in Wiring Systems.

  3. Repair the circuits if necessary.

    4. Refer to Wiring Repairs in Wiring Systems.

Was the condition corrected?

--

Go to Step 16

--

13

Inspect CKT 1228 (RED/BLK) and CKT 1229 (LT BLU/WHT) for a shorted together condition.

Refer to General Electrical Diagnosis in Wiring Systems.

Was the condition corrected?

--

Go to Step 16

--

14
  1. Inspect CKT 1228 (RED/BLK) for a short to ground.

    2. Refer to General Electrical Diagnosis in Wiring Systems.

  2. Inspect CKT 1229 (LT BLU/WHT) for a short to ground.

    3. Refer to General Electrical Diagnosis in Wiring Systems.

  3. Repair the circuits if necessary. Refer to Wiring Repairs in Wiring Systems.

Was the shorted to ground condition corrected?

--

Go to Step 16

--

15

Replace the PCM.

Refer to Powertrain Control Module Replacement/Programming in Engine Controls.

Is the replacement complete?

--

Go to Step 13

--

16

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Ensure the following conditions are met:
    4. • The engine is running.
    • The PC duty cycle is 2-95%.
  4. Select Specific DTC.
  5. Enter DTC P0748.

Has the test run and passed?

--

System OK

Go to Step 1