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Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC K Pickup - 4WD 🢒 DTC 🢒 DTC P0748 Pressure Control Solenoid Circuit Electrical

DTC P0748 Pressure Control Solenoid Circuit Electrical Gas


Object Number: 40805 Size: MF
Automatic Transmission Components
Automatic Transmission Controls Schematics Diesel
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Pressure Control Solenoid Valve (PC Sol. Valve) is a Vehicle Control Module (VCM) controlled device that regulates the transmission line pressure. The VCM compares Throttle Position (TP) Sensor voltage, engine RPM, and other inputs in order to determine the appropriate line pressure for a given load. The VCM regulates the pressure by applying a varying amperage to the PC Sol. Valve. The applied amperage varies from 0.1 amps for maximum line pressure to 1.1 amps for minimum line pressure. The VCM monitors the applied amperage.

If the VCM detects a PC duty cycle that exceeds 95% or less than 1.9%, then DTC P0748 sets. DTC P0748 is a type D DTC.

Conditions for Setting the DTC
    • The system voltage is greater than 10 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.
    • The PC duty cycle exceeds 95% or is less than 1.9%.
    • All conditions met for 200 milliseconds (0.2 seconds).

Action Taken When the DTC Sets
    • The VCM does not illuminate the Malfunction Indicator Lamp (MIL).
    • The VCM disables the PC Sol. Valve, defaulting the transmission to maximum line pressure.
    • The VCM freezes shift adapts.
    • DTC P0748 is stored in VCM history.

Conditions for Clearing the DTC
    • A scan tool can clear the DTC from the VCM history. The VCM clears the DTC from the VCM history if the vehicle completes 40 warm-up cycles without a failure reported.
    • The VCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the VCM.

Diagnostic Aids
    • Inspect the wiring at the VCM, the transmission connector and all other circuit connecting points for the following conditions:
       - A bent terminal
       - A backed out terminal
       - A damaged terminal
       - Poor 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 VCM to command the PC Sol. Valve.

    2.

  2. This step tests the PC Sol. Valve and the A/T wiring harness Assy. for incorrect resistance.

    3.

  3. This step tests the PC Sol. 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 Sol. Valve Application.

    5.

  5. This step tests the entire PC Sol. Valve circuit up to the VCM for continuity.

    6.

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

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 (5.7L) or Powertrain On Board Diagnostic (OBD) System Check (7.4L)

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 for reference. The Clear Info function will erase the stored Failure Records from the VCM.

  3. Record the DTC Failure Records.
  4. With the transmission in Park, start the engine.
  5. 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 DMM and the J 35616 Connector Test Adapter Kit, measure the resistance between terminals C and D.

Is the resistance within the specified value?

3-7Ω

Go to Step 6

Go to Step 4

4
  1. Disconnect the Automatic Transmission Wiring Harness Assembly at the PC Sol. Valve.
  2. Measure the resistance of the PC Sol. 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 Internal Wiring Harness Replacement, in On-Vehicle Service.

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?

9Ω

Go to Step 7

Go to Step 9

7
  1. Inspect the Automatic Transmission Wiring Harness Assembly (circuits 1228 and 1229) for a short to ground condition.

    2. Refer to General Electrical Diagnosis in Wiring Systems.

  2. Replace the harness if necessary.

    3. Refer to Internal Wiring Harness Replacement, in On-Vehicle Service.

Did you find a shorted condition?

--

Go to Step 16

Go to Step 8

8

Replace the PC Sol. Valve.

Refer to Pressure Regulator Valve Replacement, in On-Vehicle Service.

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 Jumper Harness from the transmission side of the 20-way connector (Automatic Transmission Connector End View).
  2. Reconnect the transmission 20-way connector.
  3. Disconnect the C3 (grey/clear) VCM connector.
  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 circuit 1228 for an open.

    2. Refer to General Electrical Diagnosis in Wiring Systems.

  2. Inspect circuit 1229 for an open.

    3. Refer to General Electrical Diagnosis in Wiring Systems.

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

Did you find and repair the open condition?

--

Go to Step 16

--

13

Inspect circuits 1228 and 1229 for a shorted together condition.

Refer to General Electrical Diagnosis in Wiring Systems.

Did you find and repair the condition?

--

Go to Step 16

--

14
  1. Inspect circuit 1228 for a short to ground.

    2. Refer to General Electrical Diagnosis in Wiring Systems.

  2. Inspect circuit 1229 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.

Did you find and repair the shorted to ground condition?

--

Go to Step 16

--

15

Replace the VCM.

Refer to VCM Replacement/Programming (5.7L) or VCM Replacement/Programming (7.4L) with KS Calibration Prom.

Is the replacement complete?

--

Go to Step 13

--

16

In order to verify your repair, perform the following procedure:

  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. Enter DTC P0748.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1

DTC P0748 Pressure Control Solenoid Circuit Electrical Diesel


Object Number: 40783 Size: MF
Automatic Transmission Components
Automatic Transmission Controls Schematics Diesel
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Pressure Control Solenoid Valve (PC Sol. Valve) is a Powertrain Control Module (PCM) controlled device that regulates the transmission line pressure. The PCM compares the Accelerator Pedal Position (APP) Sensor voltage, engine RPM, and other inputs in order to determine the appropriate line pressure for a given load. The PCM regulates the pressure by applying a varying amperage to the PC Sol. Valve. The applied amperage varies from 0.1 amps for maximum line pressure to 1.1 amps for minimum line pressure. The PCM monitors the circuit amperage.

If the PCM detects a PC duty cycle that exceeds 95% or is less than 1.9%, then DTC P0748 sets. DTC P0748 is a type D DTC.

Conditions for Setting the DTC
    • The system voltage is 9.0-16.0 volts.
    • The engine must be running greater than 475 RPM for at least 7 seconds.
    • The PC duty cycle exceeds 95% or is less than 1.9%.
    • All conditions 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 Sol. Valve, defaulting the transmission to maximum line pressure.
    • The PCM freezes shift adapts.
    • DTC P0748 is stored in PCM history.

Conditions for Clearing the DTC
    • A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported.
    • The PCM cancels the DTC default actions when the fault no longer exists and the ignition 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 bent terminal
       - A backed out terminal
       - A damaged terminal
       - Poor 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.
    • Inspect for any transmission DTCs that may have reset.

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 Sol. Valve.

    2.

  2. This step tests the PC Sol. Valve and the Automatic Transmission Wiring Harness Assembly for incorrect resistance.

    3.

  3. This step tests the PC Sol. 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 Sol. Valve Application.

  5. This step tests the entire PC Sol. valve circuit for proper resistance.

    6.

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

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 for reference. Using the Clear Info function will erase the stored Failure Records from the PCM.

  3. Record the DTC Failure Records, then clear the DTC.
  4. With the engine running, put the transmission in Park.
  5. Using the scan tool transmission output control function, 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?

0.16

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn the ignition OFF.
  2. Disconnect the transmission 20-way connector (additional DTC's may set).
  3. Install the J 39775 Jumper Harness on the transmission side of the 20-way connector.
  4. Measure the resistance between terminals C and D. Use the J 39200 DMM and the J 35616 Connector Test Adapter Kit.

Is the resistance within the specified value?

3-7Ω

Go to Step 6

Go to Step 4

4
  1. Disconnect the Automatic Transmission Wiring Harness Assembly at the PC Sol. Valve.
  2. Measure the resistance of the PC Sol. 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 Internal Wiring Harness Replacement, in On-vehicle Service.

Is the replacement complete?

--

Go to Step 16

--

6

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

Is the resistance less than the specified value?

9Ω

Go to Step 7

Go to Step 9

7
  1. Inspect the Automatic Transmission Wiring Harness Assembly (circuits 1228 and 1229), for a short to ground condition.

    2. Refer to Electrical Diagnosis.

  2. Replace the harness if necessary.

Did you find the condition?

--

Go to Step 16

Go to Step 8

8

Important: Refer to test description Step 8 for information on component replacement.

Replace the PC Sol. Valve.

Refer to Pressure Regulator Replacement, in On-Vehicle Service.

Is the replacement complete?

--

Go to Step 16

--

9

  1. Disconnect the J 39775 Jumper Harness from the transmission side of the 20-way connector.
  2. Reconnect the transmission 20-way connector.
  3. Disconnect the C1 (32 Pin/Brown) PCM connector.
  4. Measure the resistance between terminals C1-C7 and C1-C15.

Is the resistance within the specified range?

3-7 Ω

Go to Step 10

Go to Step 11

10

Measure the resistance between terminal C1-C7 and a good ground.

Is the resistance greater than the specified value?

7 Ω

Go to Step 15

Go to Step 14

11

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

7 Ω

Go to Step 12

Go to Step 13

12
  1. Inspect circuit 1228 and circuit 1229 for an open.

    2. Refer to General Electrical Diagnosis Procedures.

  2. Repair the circuits if necessary.

Refer to Wiring Repairs.

Did you find and repair the open condition?

--

Go to Step 16

Go to Step 12

13
  1. Inspect circuits 1228 and 1229 for a shorted condition. Refer to General Electrical Diagnosis Procedures.
  2. Repair the circuits if necessary. Refer to Wiring Repairs.

Did you find and repair a shorted condition?

--

Go to Step 16

--

14

Inspect circuit 1228 and circuit 1229 for a short to ground. Refer to General Electrical Diagnosis Procedures.

Did you find and repair the shorted to ground condition?

--

Go to Step 16

--

15

Replace the PCM.

Refer to Powertrain Control Module Replacement/Programming .

Is the replacement complete?

--

Go to Step 16

--

16

In order to verify your repair, perform the following procedure:

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

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1