DTC P0748 Pressure Control Solenoid Circuit Electrical. Buick Roadmaster 1996

For 1990-2009 cars
Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The Pressure Control Solenoid (PC Sol.) Valve is a PCM-controlled device that regulates the transmission line pressure. The PCM compares the TP voltage, the 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 to 1.1 amps. The applied amperage is monitored by the PCM.

When the PCM detects a continuous open or a continuous short to ground in the PC Sol. Valve circuit, then DTC P0748 sets. DTC P0748 is a type D DTC.

### Conditions for Setting the DTC

• | The system voltage is 10-17 volts.

• | The PCM recognizes that the Pressure Control Solenoid Valve has reached the valve's electrical high limit.

• | The PCM recognizes that the Pressure Control Solenoid Valve has reached the valve's electrical low limit.

### Action Taken When the DTC Sets

• | The PCM freezes shift adapts from being updated.

• | The PCM will not illuminate the Malfunction Indicator Lamp (MIL).

### 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 for any poor electrical connections at the PCM. Inspect the wiring at the transmission 20-way connector. Look 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

• | When diagnosing for an intermittent short or an open condition, massage the wiring harness while watching the test equipment for a change.

### Test Description

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

1. This step verifies that the PCM can command the PC Sol. Valve.

2. This step verifies that the PC Sol. Valve has the correct resistance. This step verifies that the Automatic Transmission wiring harness has the correct resistance.

#### DTC P0748 Pressure Control Solenoid Valve (PC Sol. Valve) Circuit - Electrical

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.

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 data.

3. Record the DTC Failure Records.
4. While the engine is operating, put the transmission in Park.
5. Using the scan tool, apply 0.1-1.0 amp while observing PC Ref Current and PC Act. Current.

Does the PC Act. Current remain within the specified range?

PC Ref Current ± 0.16 amp

Go to Diagnostic Aids

Go to Step 3

3

1. Turn the ignition switch to the OFF position.
2. Disconnect the transmission 20-way connector.
3. Install the J 39775 Jumper Harness on the transmission side of the 20-way connector.
4. Using the J 39200 DVOM and J 35616-A Connector Test Adapter Kit, measure the resistance between terminals C and D.

Is the resistance within the specified range?

3-7ohms

Go to Step 7

Go to Step 4

4

1. Remove the transmission oil pan. Refer to Oil Pan Replacement .
2. Disconnect the Automatic Transmission wiring harness at the PC Solenoid Valve.
3. Measure the resistance of the PC Solenoid Valve.

Is the resistance within the specified range?

3-7ohms

Go to Step 6

Go to Step 5

5 | Replace the PC Solenoid Valve. Refer to PC Solenoid Valve Replacement, in On-Vehicle Service. Is the replacement complete? | -- | Go to Step 10 | --
6 | Repair the Automatic Transmission wiring harness for an open. Refer to Electrical Diagnosis, Section 8. Is the repair complete? | -- | Go to Step 11 | --
7 | Inspect circuits 1228 and 1229 for an open. Repair circuits 1228 and 1229 if necessary. Refer to Electrical Diagnosis, Section 8. Did you find and correct a problem? | -- | Go to Step 11 | Go to Step 8
8 | Inspect circuits 1228 and 1229 for a short to ground. Inspect circuits 1228 and 1229 for poor connections. Refer to Electrical Diagnosis, Section 8. Did you find and correct a problem? | -- | Go to Step 11 | Go to Step 9

9

Inspect the PCM connector terminals for the following conditions:

• | Damaged connector pins

• | Backed out connector pins

• | Weak terminal tension

Repair the connectors if necessary.

Did you find and correct a problem?

--

Go to Step 11

Go to Step 10

10 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming , Section 6. Is the replacement complete? | -- | Go to Step 11 | --

11

1. After the repair is complete, select DTC.
2. Select Clear Info.

• | Ensure that the duty cycle is not at the duty cycle's electrical high limit.

• | Ensure that the duty cycle is not at the duty cycle's electrical low limit.

3. Select Specific DTC. Enter DTC P0748.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1