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For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 1997 🢒 Isuzu - N Series 🢒 Transmission/Transaxle 🢒 Automatic Transmission - 4L80-E 🢒 DTC P0748 Pressure Control Solenoid Circuit Electrical

Object Number: 40805 Size: MF
Automatic Transmission Components Gas
Automatic Transmission Controls Schematics 5.7 and 7.4 L Gas Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Pressure Control Solenoid Valve (PC Sol. Valve) is a Vehicle Control Module (VCM) controlled device that regulates the transmission line pressure. The VCM compares Throttle Position (TP) Sensor voltage, engine RPM, and other inputs in order to determine the appropriate line pressure for a given load. The VCM regulates the pressure by applying a varying amperage to the PC Sol. Valve. The applied amperage varies from 0.1-1.1 amps. The VCM monitors the applied amperage.

If the VCM detects a continuous open or short to ground in the PC Sol. Valve circuit or the PC Sol. Valve, then DTC P0748 sets. DTC P0748 is a type D DTC.

Conditions for Setting the DTC
    • The system voltage is 10-16 volts.
    • The engine must be running more than 475 RPM for at least 7 seconds and not in fuel cut off.
    • The difference in the commanded and the measured return amperage is greater than 0.16 amps.
    • All conditions met for 200 milliseconds (0.2 seconds).

Action Taken When the DTC Sets
    • The VCM disables the PC Sol. Valve, defaulting the transmission to maximum line pressure.
    • The VCM freezes shift adapts.

Conditions for Clearing the DTC
  1. A scan tool can clear the DTC from the VCM history. The VCM clears the DTC from the VCM history if the vehicle completes 40 warm-up cycles without a failure reported.
  2. The VCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the VCM.

Diagnostic Aids
    • Inspect the wiring for poor electrical connections at the VCM. Inspect the wiring for poor electrical connections at the transmission 20-way connector. Look for the following problems:
       - A bent terminal
       - A backed out terminal
       - A damaged terminal
       - Poor terminal tension
       - A chafed wire
       - A broken wire inside the insulation
    • When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
    • First diagnose and clear any engine DTCs or TP Sensor codes that are present. Then inspect for any transmission DTCs that may have reset.
    • Inspect for improperly wired after-market equipment.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests the ability of the VCM to command the PC Sol. Valve.

    2.

  2. This step tests the PC Sol. Valve and the Automatic Transmission Wiring Harness Assembly for incorrect resistance.

    3.

  3. When performing this step refer to Product Service Bulletin #9474L80E-07 for PC Sol. Valve Application.

P0748

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Install the Scan Tool ®.
  2. With the engine OFF, turn the ignition switch to the RUN position.

    3. Important: Before clearing the DTCs, use the scan tool in order to record the Failure Records for reference. The Clear Info function will erase the data.

  3. Record the DTC Failure Records.
  4. With the transmission in Park, start the engine.
  5. Using the transmission output control function on the scan tool, apply 0.1-1.0 amps while observing the PC Ref. Current and the PC Act. Current.

Is the PC Act. Current reading always within the specified value of the PC Ref. Current?

0.16 amp

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn the ignition OFF.
  2. Disconnect the transmission 20-way connector.
  3. Install the J 39775 Jumper Harness on the transmission side of the 20-way connector. ( Automatic Transmission Connector End View )
  4. Using the J 39200 DMM and the J 35616 Connector Test Adapter Kit, measure the resistance between terminals C and D.

Is the resistance within the specified value?

3-7Ω

Go to Step 6

Go to Step 4

4
  1. Disconnect the Automatic Transmission Wiring Harness Assembly at the PC Sol. Valve.
  2. Measure the resistance of the PC Sol. Valve.

Is the resistance within the specified range?

3-7Ω

Go to Step 5

Go to Step 8

5

Replace the Automatic Transmission Wiring Harness Assembly.

Refer to Interior Wiring Harness Replacement, in On-Vehicle Service.

Is the replacement complete?

--

Go to Step 13

--

6

Measure the resistance from terminal C to the transmission case.

Is the resistance less than the specified value?

9Ω

Go to Step 7

Go to Step 9

7
  1. Inspect the Automatic Transmission Wiring Harness Assembly for a short to ground.

    2. Refer to Electrical Diagnosis, Section 8.

  2. Replace the harness if necessary.

    3. Refer to Interior Wiring Harness Replacement, in On-Vehicle Service.

Did you find a problem?

--

Go to Step 13

Go to Step 8

8

Important: Refer to Test Description Step 8 for information on component replacement.

Replace the PC Sol. Valve.

Refer to Pressure Regulator Replacement, in On-Vehicle Service.

Is the replacement complete?

--

Go to Step 13

--

9
  1. Disconnect the J 39775 Jumper Harness from the transmission side of the 20-way connector.
  2. Reconnect the transmission 20-way connector.
  3. Disconnect the C3 (grey/clear) VCM connector.
  4. Measure the resistance from terminal C3-6 to ground.

Is the resistance greater than the specified value?

9Ω

Go to Step 10

Go to Step 11

10
  1. Inspect circuit 1228 for an open.
  2. Inspect circuit 1229 for an open.
  3. Repair the circuits if necessary.

Refer to Electrical Diagnosis, Section 8.

Did you find a problem?

--

Go to Step 13

Go to Step 12

11
  1. Inspect circuit 1228 for a short to ground.
  2. Inspect circuit 1229 for a short to ground.
  3. Repair the circuits if necessary.

    4. Refer to Electrical Diagnosis, Section 8.

Did you find a problem?

--

Go to Step 13

Go to Step 12

12

Replace the VCM.

Refer to VCM Replacement/Programming , Section 6.

Is the replacement complete?

--

Go to Step 13

--

13

In order to verify your repair, perform the following procedure:

  1. Select DTC.
  2. Select Clear Info.
  3. Ensure the following conditions are met:
    4. • The engine is running.
    • The difference between the PC Sol. Valve actual return amperage and the desired amperage is less than 0.16 amp.
  4. Select Specific DTC. Enter DTC P0748.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1