Circuit Description
The pressure control (PC) solenoid valve is a powertrain control module (PCM) controlled device that regulates the transmission line pressure. The PCM compares throttle position (TP) sensor voltage, engine RPM, and other inputs in order to determine the appropriate line pressure for a given load. The PCM regulates line pressure by applying a varying duty cycle to the PC solenoid valve based on the resistance of the solenoid, and the amperage needed to obtain optimum line pressure. The applied amperage varies from 0.1 amps for maximum line pressure to 1.1 amps for minimum line pressure.
If the PCM detects a PC duty cycle that exceeds 95 percent or less than 1.9 percent, then DTC P0748 sets. DTC P0748 is a type C DTC.
Conditions for Running the DTC
| • | The system voltage is greater than 11 volts at -40°C (-40°F) TFT or 12 volts at 150°C (302°F) TFT. |
| • | The engine must be running more than 275 RPM for at least 7 seconds. |
| • | The PC solenoid is commanded on. |
Conditions for Setting the DTC
| • | The PC duty cycle exceeds 95 percent or is less than 1.9 percent. |
| • | All conditions are met for 700 milliseconds (0.5 seconds). |
Action Taken When the DTC Sets
| • | The PCM does not illuminate the malfunction indicator lamp (MIL). |
| • | The PCM disables the PC solenoid valve, defaulting the transmission to maximum line pressure. |
| • | The PCM freezes shift adapts. |
| • | 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 clears the DTC from PCM history. |
| • | 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 ignition switch is OFF long enough in order to power down the PCM. |
Diagnostic Aids
| • | Inspect for improperly wired after-market equipment. |
| • | DTC P0748 defaults to an elevated line pressure condition which may result in partial TCC apply. This may produce an idle surge that could stall the engine. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step tests the ability of the PCM to command the PC solenoid valve.
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This step tests the PC solenoid valve and the AT wiring harness assembly for correct resistance.
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This step tests the PC solenoid valve and the internal wiring harness for a short to ground.
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This step tests the entire PC solenoid valve circuit up to the PCM for continuity.
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This step tests for a short to ground in the PC solenoid valve high control, solenoid A, circuit (CKT 1228) and the PC solenoid valve low control, solenoid A, circuit (CKT 1229), of the engine harness.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls in Engine Controls - 6.0L or Diagnostic System Check - Engine Controls in Engine Controls - 8.1L |
Important: Before clearing the DTCs, use the scan tool in order to record the Failure Records. Using the Clear Info Function erases the Failure Records from the PCM. Refer to Line Pressure . Is the PC Act. current reading always within the specified value of the PC Ref. current? | 0.16 amp | Go to Intermittent Conditions in Engine Controls - 6.0L or Intermittent Conditions in Engine Controls - 8.1L | Go to Step 3 | |
Does the resistance measure within the specified value? | 3-7 ohms | Go to Step 7 | Go to Step 4 | |
4 | Is the resistance greater than the specified value? | 7 ohms | Go to Step 5 | Go to Step 6 |
5 |
Refer to Circuit Testing in Wiring Systems. Did you find the condition? | 7 ohms | Go to Step 15 | Go to Step 14 |
Test the high control circuit (CKT 1228) and the low control circuit (CKT 1229) of the PC solenoid valve for a short 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 15 | Go to Step 14 | |
7 |
Refer to Automatic Transmission Inline Harness Connector End View and Circuit Testing in Wiring Systems. Did you find the condition? | -- | Go to Step 15 | Go to Step 8 |
8 |
Refer to Automatic Transmission Inline Harness Connector End View and Circuit Testing in Wiring Systems. Did you find the condition? | -- | Go to Step 15 | Go to Step 9 |
Does the resistance measure within the specified range? | 3-7 ohms | Go to Step 13 | Go to Step 10 | |
Does the resistance measure greater than the specified value? | 7 ohms | Go to Step 11 | Go to Step 12 | |
11 |
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | -- |
12 | Test the high control circuit (CKT 1228) and the low control circuit (CKT 1229) of the PC solenoid valve for a short together between the PCM and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | -- |
13 |
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 16 |
14 | Replace the pressure control solenoid valve. Refer to Valve Body and Pressure Switch Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- |
15 | Replace the automatic transmission wiring harness assembly. Refer to Valve Body and Pressure Switch Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- |
16 | Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls - 6.0L or Powertrain Control Module Replacement in Engine Controls - 8.1L. Did you complete the replacement? | -- | Go to Step 17 | -- |
17 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK | Go to Step 1 |
