Circuit Description
The pressure control (PC) solenoid valve is an electronic device that regulates transmission line pressure based on the current flow through its coil winding. The magnetic field produced by the coil moves the solenoid's internal valve which varies pressure to the pressure regulator valve. The vehicle control module (VCM) controls the PC solenoid valve by applying a varying amount of amperage to the solenoid. The applied amperage can vary from 0.1 to 1.1 amps. Low amperage (0.1 amp) indicates high line pressure. High amperage (1.1 amps) indicates low line pressure. The duty cycle of the PC solenoid valve is expressed as a percentage of energized ON time. Zero percent indicates zero ON time (non-energized) or no current flow. Approximately 60% at idle indicates maximum ON time (energized) or high current flow. The VCM determines the appropriate line pressure for a given load by comparing the throttle position (TP) voltage, the engine speed and other inputs.
When the VCM detects a continuous open or short to ground in the PC solenoid valve circuit or the PC solenoid valve, then DTC P0748 sets. DTC P0748 is a type D DTC.
Conditions for Running the DTC
| • | The system voltage is 10-19 volts. |
| • | The engine is running. |
Conditions for Setting the DTC
The PC solenoid valve duty cycle reaches its high limit (approximately 95%) or low limit (approximately 0%).
Action Taken When the DTC Sets
| • | The VCM does not illuminate the malfunction indicator lamp (MIL). |
| • | The VCM freezes shift adapts from being updated. |
| • | The PC solenoid valve is OFF. |
| • | 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 condition, massage the wiring harness while watching the test equipment for a change. |
| • | DTC P0748 may set under low voltage conditions caused by high electrical system demands. |
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 automatic transmission (A/T) 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) or Powertrain On Board Diagnostic (OBD) System Check (5.0L and 5.7L) in Engine Controls | |
Important: Before clearing the DTC, use the scan tool in order to record the Failure Records. Using the Clear Info function erases the Failure Records from the VCM. Is the PC Sol. Actual Current always within the specified value of the PC Sol. Ref. Current? | 0.16 amp | Go to Diagnostic Aids | ||
Refer to Automatic Transmission Inline Harness Connector End View . Is the resistance within the specified range? | 3-7 ohms | |||
4 | Is the resistance greater than the specified value? | 7 ohms | ||
5 | Inspect circuit 1228 (PPL) and circuit 1229 (LT BLU) of the A/T wiring harness assembly for an open condition. Refer to General Electrical Diagnosis in Wiring Systems. Did you find an open condition? | -- | ||
6 | Is the resistance less than the specified value? | 3 ohms | -- | |
7 | Inspect circuit 1228 (PPL) and circuit 1229 (LT BLU) of the A/T wiring harness assembly for a shorted together condition. Refer to General Electrical Diagnosis in Wiring Systems. Did you find a shorted together condition? | -- | ||
8 | Measure the resistance from terminal C to the transmission case. Is the resistance less than the specified value? | 9 ohms | ||
9 | Inspect circuit 1228 (PPL) and circuit 1229 (LT BLU) of the A/T wiring harness assembly for a short to ground condition. Refer to General Electrical Diagnosis in Wiring Systems. Did you find a short to ground condition? | -- | ||
10 | Replace the PC solenoid valve. Refer to Control and Shift Solenoids Replacement. Is the replacement complete? | -- | -- | |
11 |
Is the resistance within the specified range? | 3-7 ohms | ||
12 | Is the resistance greater than the specified value? | 7 ohms | ||
13 |
Refer to General Electrical Diagnosis in Wiring Systems. Refer to Wiring Repairs in Wiring Systems. Did you find and correct an open condition? | -- | -- | |
14 | Is the resistance less than the specified value? | 3 ohms | -- | |
15 |
Refer to General Electrical Diagnosis in Wiring Systems. Refer to Wiring Repairs in Wiring Systems. Did you find and correct a shorted together condition? | -- | -- | |
16 | Using the J 39200 DMM and the J 35616-A connector test adapter kit, measure the resistance from terminal C3-6 to ground. Is the resistance less than the specified value? | 9 ohms | ||
17 |
Refer to General Electrical Diagnosis in Wiring Systems. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the short to ground condition? | -- | -- | |
18 | Replace the A/T wiring harness assembly. Refer to TCC PWM Solenoid, TCC Solenoid, and Wiring Harness Replacement. Is the replacement complete? | -- | -- | |
19 | Replace the VCM. Refer to VCM Replacement/Programming (4.3L) or VCM Replacement/Programming (5.0L and 5.7L) in Engine Controls. Is the replacement complete? | -- | -- | |
20 | Perform the following procedure in order to verify the repair:
The difference between the scan tool PC Sol. Actual Current and the PC Sol. Ref. Current is less than 0.16 amp. Has the test run and passed? | -- | System OK |
