Circuit Description
The PCM uses the pressure control (PC) solenoid valve in order to regulate the transmission line pressure. The PC solenoid valve consists of an electrical connector, a coil, an armature, a regulating spring, and a poppet valve. The PC solenoid valve is attached to the upper control body. The PCM compares TP voltage, fluid temperature, gear states, and other inputs in order to determine the line pressure appropriate for a given load. The PCM regulates the pressure by applying a varying amperage to the PC solenoid valve. The applied amperage varies from 0.1 amps for maximum line pressure to 1.1 amps for minimum line pressure. The PCM then monitors the amperage at the return line.
When the PCM detects a continuous open, short to ground or short to voltage 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 8-18 volts.
Conditions for Setting the DTC
The PC solenoid valve duty cycle is 0% or greater than 95%.
Action Taken When the DTC Sets
| • | The PCM does not illuminate the malfunction indicator lamp (MIL). |
| • | The PCM commands maximum line pressure (0 amps). |
| • | The PCM freezes shift adapts from being updated. |
| • | The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Failure Records. |
| • | The PCM stores DTC P0748 in PCM history. |
Conditions for Clearing the DTC
| • | A scan tool can clear the DTC. |
| • | The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without a non-emission-related diagnostic fault occurring. |
| • | The PCM 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 PCM. |
Diagnostic Aids
| • | Inspect the connectors at the PCM, the PC solenoid valve 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. |
| • | Extended engine cranking with a weak battery could set DTC P0748. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step verifies the ability of the PCM to command the PC solenoid valve.
-
This step verifies that the automatic transmission wiring harness and the PC solenoid valve have correct 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 (2.2L) or Powertrain On Board Diagnostic (OBD) System Check (2.4L) | |
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 PCM. Does the PC Sol. Actual Current amp reading differ from the PC Sol. Ref. Current amp reading by no more than the specified amount? | 0.16 amps | 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 |
Refer to Circuit Testing in Wiring Systems. Did you find a condition? | -- | ||
6 | Test the controlled power feed circuit (CKT 1228) and the controlled ground circuit (CKT 1229) of the PC solenoid valve for being shorted together between the AT inline 20-way connector and the PC solenoid valve. Refer to Circuit Testing in Wiring Systems. Did you find a condition? | -- | ||
7 | Measure the resistance from terminal D of the J 44152 to a good ground. Refer to Automatic Transmission Inline Harness Connector End View . Is the resistance less than the specified value? | 1000 ohms | ||
8 |
Refer to Circuit Testing in Wiring Systems. Did you find a condition? | -- | ||
9 |
Refer to Automatic Transmission Inline Harness Connector End View . Is the resistance less than the specified value? | 10 ohms | ||
10 | Test the controlled ground circuit (CKT 1229) of the PC solenoid valve for a short to ground between the PCM connector C2 and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | -- | |
11 | Using the J 39200 DMM and the J 35616 , measure the resistance between terminal D of the J 44152 and terminal 9 of the PCM connector C2. Refer to Automatic Transmission Inline Harness Connector End View . Is the resistance less than the specified value? | 10 ohms | ||
12 | Test the controlled ground circuit (CKT 1229) of the PC solenoid valve for an open between the PCM connector C2 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 | Using the J 39200 DMM and the J 35616 measure the resistance from terminal C of the J 44152 to a good ground. Refer to Automatic Transmission Inline Harness Connector End View . Is the resistance less than the specified value? | 10 ohms | ||
14 | Test the controlled power feed circuit (CKT 1228) of the PC solenoid valve for a short to ground between the PCM connector C2 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 | Using the J 39200 DMM and the J 35616 measure the resistance between terminal C of the J 44152 and terminal 6 of the PCM connector C2. Refer to Automatic Transmission Inline Harness Connector End View . Is the resistance less than the specified value? | 10 ohms | ||
16 | Test the controlled power feed circuit (CKT 1228) of the PC solenoid valve for an open between the PCM connector C2 and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | -- | |
17 | Replace the automatic transmission wiring harness. Refer to Transmission Overhaul in the 4T40-E/4T45-E section of the Transmission Unit Repair Manual. Did you complete the replacement? | -- | -- | |
18 | Replace the PC solenoid valve. Refer to Control and Shift Solenoids Replacement. Did you complete the replacement? | -- | -- | |
19 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming (2.2L) or Powertrain Control Module Replacement/Programming (2.4L) in Engine Controls. Did you complete the replacement? | -- | -- | |
20 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK |
