Circuit Description
The pressure control (PC) solenoid valve regulates actuator feed fluid passing through the solenoid into torque signal pressure. The PCM uses a pulse width modulated signal in order to control the torque signal pressure. The PCM compares various inputs in order to determine the appropriate pressure for a given load. The PCM varies the current to the PC solenoid valve from 0.1 amps, for maximum line pressure to 1.1 amps, for minimum line pressure. An internal current monitor within the PCM provides feedback in order to determine actual PC solenoid valve current draw.
If 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 at least 10.7 volts. |
| • | The engine speed is 400 RPM or greater. |
Conditions for Setting the DTC
The PC solenoid valve feedback circuit indicates a continuous open, short to ground or short to voltage for greater than 0.1 second.
Action Taken When the DTC Sets
| • | The PCM does not illuminate the malfunction indicator lamp (MIL). |
| • | SERVICE TRANSMISSION displays on the driver information center (DIC). |
| • | The PCM commands maximum line pressure. |
| • | The PCM freezes transmission adaptive functions. |
| • | 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 DIC/DTC
| • | The PCM clears the DIC when the condition no longer exists. |
| • | 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 the DTC passes. |
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 Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls 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 PCM. Does the PC Sol. Actual Current vary from the PC Sol. Ref. Current by more than the specified amount? | 0.05 amps | Go to Step 3 | Go to Intermittent Conditions in Engine Controls | |||||
Refer to Automatic Transmission Inline 20-Way Connector End View . Is the resistance within the specified range? | 3-8 ohms | Go to Step 7 | Go to Step 4 | |||||
4 | Is the resistance greater than the specified value? | 8 ohms | Go to Step 5 | Go to Step 6 | ||||
5 |
Refer to Testing for Continuity in Wiring Systems. Did you find a condition? | -- | Go to Step 19 | Go to Step 20 | ||||
6 | Test the high control circuit (CKT 1228) and the low control 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 the condition? | -- | Go to Step 19 | Go to Step 20 | ||||
7 | Measure the resistance from terminal C of the J 44152 to ground. Refer to Automatic Transmission Inline 20-Way Connector End View . Is the resistance less than the specified value? | 10 ohms | Go to Step 8 | Go to Step 9 | ||||
8 |
Refer to Testing for Short to Ground in Wiring Systems. Did you find a condition? | -- | Go to Step 19 | Go to Step 20 | ||||
9 | Measure the resistance between terminal C and all other terminals, except terminal D, of the J 44152 . Refer to Automatic Transmission Inline 20-Way Connector End View . Is the resistance between terminal C and any other terminal, except terminal D, less than the specified value? | 100 ohms | Go to Step 19 | Go to Step 10 | ||||
10 |
Refer to Automatic Transmission Inline 20-Way Connector End View . Is the resistance less than the specified value? | 10 ohms | Go to Step 11 | Go to Step 12 | ||||
11 | Test the low control circuit (CKT 1229) of the PC solenoid valve for a short to ground between the PCM connector C1 and the AT inline 20-way connector. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 22 | -- | ||||
12 | Using the DMM and the J 35616 , measure the resistance between terminal D of the J 44152 and terminal 67 of the PCM connector C1. Refer to Automatic Transmission Inline 20-Way Connector End View . Is the resistance less than the specified value? | 10 ohms | Go to Step 14 | Go to Step 13 | ||||
13 | Test the low control circuit (CKT 1229) of the PC solenoid valve for an open between the PCM connector C1 and the AT inline 20-way connector. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 22 | -- | ||||
14 | Using the DMM and the J 35616 measure the resistance from terminal C of the J 44152 to ground. Refer to Automatic Transmission Inline 20-Way Connector End View . Is the resistance less than the specified value? | 10 ohms | Go to Step 15 | Go to Step 16 | ||||
15 | Test the high control circuit (CKT 1228) of the PC solenoid valve for a short to ground between the PCM connector C1 and the AT inline 20-way connector. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 22 | -- | ||||
16 | Using the DMM and the J 35616 measure the resistance between terminal C of the J 44152 and terminal 69 of the PCM connector C1. Refer to Automatic Transmission Inline 20-Way Connector End View . Is the resistance less than the specified value? | 10 ohms | Go to Step 21 | Go to Step 17 | ||||
17 | Test the high control circuit (CKT 1228) of the PC solenoid valve for an open between the PCM connector C1 and the AT inline 20-way connector. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 22 | Go to Step 18 | ||||
18 | Test the high control circuit (CKT 1228) and the low control circuit (CKT 1229) of the PC solenoid for a short to voltage. Refer to Testing for a Short to Voltage and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 22 | Go to Step 21 | ||||
19 |
Important: The automatic transmission wiring harness consists of two separate harnesses, the Automatic Transmission Wiring Harness Assembly, GM P/N 15320475 and the Automatic Transmission Wiring Extension Harness Assembly, GM P/N 15320478. In order to avoid the unnecessary replacement of parts, only replace the Automatic Transmission Wiring Harness Assembly, GM P/N 15320475. Replace the automatic transmission wiring harness. Refer to Input Speed Sensor and Wiring Harness Removal in the 4T80-E section of the Transmission Unit Repair Manual. Did you complete the replacement? | -- | Go to Step 22 | -- | ||||
20 | Replace the PC solenoid valve. Refer to Control Valve Upper Body Disassemble in the 4T80-E section of the Transmission Unit Repair Manual. Did you complete the replacement? | -- | Go to Step 22 | -- | ||||
21 | Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls. Did you complete the replacement? | -- | Go to Step 22 | -- | ||||
22 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | Go to Step 23 | Go to Step 2 | ||||
23 | With the scan tool, observe the stored information, capture info. and DTC info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List in Engine Controls | System OK |
