GM Service Manual Online
For 1990-2009 cars only

Object Number: 13279  Size: SF
Automatic Transmission Components
TFP Switch, TFT Sensor, PC Solenoid Valve, and VSS
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Pressure Control Solenoid (PCS) 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 PCS. The applied amperage varies from 0.1 to 1.1 amps. The applied amperage is monitored by the PCM.

DTC P0748 detects a continuous open in the PCS circuit. DTC P0748 detects a continuous short to ground in the PCS. DTC P0748 is a type D DTC.

Conditions for Setting the DTC

    • No system voltage DTC P0560
    • 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 freeze shift adapts from being updated.
    • The PCM does 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 open condition, massage the wiring harness while watching the test equipment for any changes.

Test Description

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

  1. This Step verifies that the PCM can command the PC Solenoid Valve.

  2. This Step verifies that the PC Solenoid 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 Solenoid 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.
  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 data.

  4. Record the DTC Failure Records.
  5. While the engine is operating, put the transmission in Park.
  6. Using the scan tool, apply 0.1 through 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 OFF.
  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 Pressure Regulator Replacement .

Is the replacement complete?

--

Go to Step 10

--

6

Repair the Automatic Transmission wiring harness for an open. Refer to Electrical Diagnosis, Section 8A.

Is the repair complete?

--

Go to Step 10

--

7

  1. Inspect circuits 1228 and 1229 for an open.
  2. Repair circuits 1228 and 1229 if necessary. Refer to Electrical Diagnosis, Section 8A.

Did you find and correct a problem?

--

Go to Step 10

Go to Step 8

8

  1. Inspect circuits 1228 and 1229 for a short to ground.
  2. Inspect circuits 1228 and 1229 for poor connections.

Refer to Electrical Diagnosis, Section 8A.

Did you find and correct a problem?

--

Go to Step 10

Go to Step 9

9

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming , Section 6

Is the replacement complete?

--

Go to Step 10

--

10

  1. After the repair is complete, select DTC.
  2. Select Clear Info.
  3. • 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.
  4. Select Specific DTC. Enter DTC P0748.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1