Circuit Description
The Pressure Control Solenoid Valve (PC Sol. Valve) is a VCM-controlled device used to regulate the transmission line pressure. The VCM compares the TP voltage, the engine RPM, and other inputs to determine the line pressure appropriate for a given load. The VCM applies a varying amperage to the PC Sol. Valve in order to regulate the pressure. The applied amperage can vary from 0.1 to 1.1 amps. The VCM monitors the amperage.
When the VCM detects a continuous open or short to ground in the PC Sol. Valve circuit or the PC Sol. Valve, then DTC P0748 sets. DTC P0748 is a type D DTC.
Conditions for Setting the DTC
| • | The system voltage is 10-17 volts. |
| • | The engine is running. |
| • | The difference between the PC Sol. Valve actual return amperage and the desired amperage is 0.16 amp or greater. |
Action Taken When the DTC Sets
| • | The VCM freezes shift adapts from being updated. |
| • | The PC Sol. Valve is OFF. |
| • | The VCM does not illuminate the Malfunction Indicator Lamp (MIL). |
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 for poor electrical connections at the VCM. Inspect the wiring for poor electrical connections 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 a change. |
Test Description
The numbers below refer to the step numbers on the diagnostic chart.
-
This step tests the ability of the VCM to command the PC Sol. Valve.
-
This step tests the PC Sol. Valve and Automatic Transmission Wiring Harness Assembly for incorrect resistance.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check (4.3L) Powertrain On Board Diagnostic (OBD) System Check (5.0L and 5.7L) | |||||
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. Is the PC Act Current always within the specified value of the PC Ref Current? | 0.16 amp | Go to Diagnostic Aids | ||||||
Is the resistance within the specified range? | 3-7ohms | |||||||
4 |
Refer to Transmission Oil Pan Removal. Is the resistance within the specified range? | 3-7ohms | ||||||
5 | Replace the A/T Wiring Harness Assy. Refer to Automatic Transmission Wiring Harness Assembly Replacement, in On-Vehicle Service. Is the replacement complete? | -- | -- | |||||
6 | Measure the resistance from terminal C to the transmission case. Is the resistance less than the specified value? | 9ohms | ||||||
7 |
Refer to Electrical Diagnosis, Section 8. Did you find a problem? | -- | ||||||
8 | Replace the PC Sol. Valve. Refer to Pressure Control Solenoid Valve Replacement, in On-Vehicle Service. Is the replacement complete? | -- | -- | |||||
9 |
Is the resistance greater than the specified value? | 9ohms | ||||||
10 |
Refer to Electrical Diagnosis, Section 8. Did you find a problem? | -- | ||||||
11 |
Refer to Electrical Diagnosis, Section 8. Did you find a problem? | -- | ||||||
12 | Replace the VCM. Refer to Section 6: VCM Replacement/Programming (4.3L) VCM Replacement/Programming (5.0L and 5.7L) Is the replacement complete? | -- | -- | |||||
13 | In order to verify your repair, perform the following procedure:
Has the test run and passed? | -- | System OK |
