DTC P0748 Pressure Control Solenoid Circuit Electrical. GMC Truck Savana 1999

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1999 🢒 Savana 🢒 Transmission/Transaxle 🢒 Automatic Transmission - 4L80-E 🢒 DTC P0748 Pressure Control Solenoid Circuit Electrical

DTC P0748 Pressure Control Solenoid Circuit Electrical Gas

Automatic Transmission Components Gas
Automatic Transmission Controls Schematics Gas
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The pressure control (PC) 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 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 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 Running 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, and not in fuel cutoff.

Conditions for Setting the DTC

•	The PC duty cycle exceeds 95% or is less than 1.9%.

•	All conditions are met for 200 milliseconds (0.2 second).

Action Taken When the DTC Sets

•	The VCM does not illuminate the malfunction indicator lamp (MIL).

•	The VCM disables the PC solenoid valve, defaulting the transmission to maximum line pressure.

•	The VCM freezes shift adapts.

•	The VCM stores DTC P0748 in VCM history.

Conditions for Clearing the DTC

•	A scan tool clears the DTC from VCM history.

•	The VCM clears the DTC from VCM history if the vehicle completes 40 warm-up cycles without a non-emission-related diagnostic fault occurring.

•	The VCM 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 VCM.

Diagnostic Aids

•	Inspect the wiring at the VCM, 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.

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

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

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

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

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

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

P0748

Step

Action

Value(s)

Yes

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

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check (4.3L) or Powertrain On Board Diagnostic (OBD) System Check (5.7L) or Powertrain On Board Diagnostic (OBD) System Check (7.4L)

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

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 VCM.

Record the Failure Records.
Clear the DTCs.
With the transmission in PARK, start the engine.
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.

Refer to the Line Pressure specification table.

Is the PC Act. current reading always within the specified value of the PC Ref. current?

0.16 amp

Go to Diagnostic Aids

Go to Step 3

Turn the ignition OFF.
Disconnect the transmission 20-way connector (additional DTCs will set).
Install the J 39775 jumper harness on the transmission side of the 20-way connector (Automatic Transmission Connector End View).
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 value?

3-7ohms

Go to Step 6

Go to Step 4

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

Is the resistance within the specified range?

3-7ohms

Go to Step 5

Go to Step 8

Replace the automatic transmission wiring harness assembly.

Refer to AT Wiring Harness Replacement.

Is the replacement complete?

Go to Step 16

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

Is the resistance less than the specified value?

7ohms

Go to Step 7

Go to Step 9

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

Refer to General Electrical Diagnosis in Wiring Systems.

Replace the harness if necessary.

Refer to AT Wiring Harness Replacement.

Was a shorted condition found?

Go to Step 16

Go to Step 8

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

Replace the PC solenoid valve.

Refer to Pressure Regulator Valve Replacement.

Is the replacement complete?

Go to Step 16

Disconnect the J 39775 jumper harness from the transmission side of the 20-way connector (Automatic Transmission Connector End View).
Reconnect the transmission 20-way connector.
Disconnect the VCM connector C3.
Measure the resistance between terminals C3-6 and C3-16.

Is the resistance within the specified range?

3-7ohms

Go to Step 10

Go to Step 11

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

Is the resistance greater than the specified value?

7ohms

Go to Step 15

Go to Step 14

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

7ohms

Go to Step 12

Go to Step 13

Inspect circuit 1228 (RED/BLK) for an open.

Refer to General Electrical Diagnosis in Wiring Systems.

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

Refer to General Electrical Diagnosis in Wiring Systems.

Repair the circuits if necessary.

Refer to Wiring Repairs in Wiring Systems.

Was an open condition found?

Go to Step 16

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

Refer to General Electrical Diagnosis in Wiring Systems.

Was the condition found?

Go to Step 16

Inspect circuit 1228 (RED/BLK) for a short to ground.

Refer to General Electrical Diagnosis in Wiring Systems.

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

Refer to General Electrical Diagnosis in Wiring Systems.

Repair the circuits if necessary.

Refer to Wiring Repairs in Wiring Systems.

Was a short to ground condition found?

Go to Step 16

Replace the VCM.

Refer to VCM Replacement/Programming (4.3L) or VCM Replacement/Programming (5.7L) or VCM Replacement/Programming (7.4L) in Engine Controls.

Is the replacement complete?

Go to Step 17

Repair the circuit as necessary.

Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

Go to Step 17

Perform the following procedure in order to verify the repair:

Select DTC.
Select Clear Info.
Ensure the following conditions are met:

•	The engine is running.

•	The PC duty cycle is 2-95%.

Select Specific DTC.
Enter DTC P0748.

Has the test run and passed?

System OK

Go to Step 1

DTC P0748 Pressure Control Solenoid Circuit Electrical Diesel

Automatic Transmission Components Diesel
Automatic Transmission Controls Schematics Diesel
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The pressure control (PC) solenoid valve is a vehicle 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 the 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% or is less than 1.9%, then DTC P0748 sets. DTC P0748 is a type D DTC.

Conditions for Running 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 greater 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% or is less than 1.9%.

•	All conditions met for 200 milliseconds (0.2 second).

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.

•	Inspect for any transmission DTCs that may have reset.

Test Description

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

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

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

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

When performing this step refer to Product Service Bulletin #9474L80E-07 for PC solenoid valve application.

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

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

P0748

Step

Action

Value(s)

Yes

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

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

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

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.

Record the Failure Records.
Clear the DTC.
With the engine running, put the transmission in PARK.
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

Turn the ignition OFF.
Disconnect the transmission 20-way connector (additional DTCs may set).
Install the J 39775 jumper harness on the transmission side of the 20-way connector.
Measure the resistance between terminals C and D. Use the J 39200 digital multimeter (DMM) and the J 35616 connector test adapter kit.

Is the resistance within the specified value?

3-7ohms

Go to Step 6

Go to Step 4