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 in the PC solenoid valve circuit, then DTC P0748 sets. DTC P0748 is a type C 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 PC solenoid valve is OFF. |
| • | The VCM freezes shift adapts from being updated. |
| • | The VCM records the operating conditions when the Conditions for Setting the DTC are met. The VCM stores this information as Failure Records. |
| • | The VCM stores DTC P0748 in VCM history. |
Conditions for Clearing the DTC
| • | A scan tool can clear the DTC. |
| • | 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/or the ignition switch is OFF long enough in order to power down the VCM. |
Diagnostic Aids
| • | Inspect the connectors at the VCM, the PC solenoid and all other circuit connecting points for an intermittent condition. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
| • | Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical Intermittents in Wiring Systems. |
| • | 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 (AT) wiring harness assembly for incorrect resistance.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain Diagnostic System Check? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check (4.3L) or Powertrain On Board Diagnostic (OBD) System Check (5.0/5.7L) 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 . Does the resistance measure within the specified range? | 3-7 ohms | |||
4 | Does the resistance measure greater than the specified value? | 7 ohms | ||
5 | Measure the resistance from terminal C of the J 44152 to the transmission case. Refer to Automatic Transmission Inline Harness Connector End View . Does the resistance measure greater than the specified value? | 250 K ohms | ||
6 |
Does the resistance measure within the specified range? | 3-7 ohms | ||
7 | Does the resistance measure greater than the specified value? | 7 ohms | ||
8 | Using the J 39200 DMM and the J 35616-A , measure the resistance from VCM connector terminal C3-6 to ground. Does the resistance measure greater than the specified value? | 250 K ohms | ||
9 | Test the controlled power feed circuit (CKT 1228) and the controlled ground circuit (CKT 1229) of the PC solenoid for an open between the AT inline 20-way connector and the PC solenoid. Refer to Circuit Testing in Wiring Systems. Did you find an open condition? | -- | ||
10 | Test the controlled power feed circuit (CKT 1228) and the controlled ground circuit (CKT 1229) of the PC solenoid for a shorted together condition between the AT inline 20-way connector and the PC solenoid. Refer to Circuit Testing in Wiring Systems. Did you find a shorted together condition? | -- | ||
11 | Test the controlled power feed circuit (CKT 1228) and the controlled ground circuit (CKT 1229) of the PC solenoid for a short to ground between the AT inline 20-way connector and the PC solenoid. Refer to Circuit Testing in Wiring Systems. Did you find a short to ground condition? | -- | ||
12 | Test the controlled power feed circuit (CKT 1228) and the controlled ground circuit (CKT 1229) of the PC solenoid for an open between the VCM connector C3 and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | -- | |
13 | Test the controlled power feed circuit (CKT 1228) and the controlled ground circuit (CKT 1229) of the PC solenoid for a shorted together condition between the VCM connector C3 and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | -- | |
14 | Test the controlled power feed circuit (CKT 1228) and the controlled ground circuit (CKT 1229) of the PC solenoid for a short to ground between the VCM connector C3 and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | -- | |
15 | Replace the PC solenoid valve. Refer to Valve Body . Did you complete the replacement? | -- | -- | |
16 | Replace the AT wiring harness assembly. Refer to Valve Body . Did you complete the replacement? | -- | -- | |
17 | Replace the VCM. Refer to VCM Replacement/Programming (4.3L) or VCM Replacement/Programming (5.0/5.7L) in Engine Controls. Did you complete the replacement? | -- | -- | |
18 | 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 |
