DTC P0748 Pressure Control Solenoid Circuit Electrical. Cadillac Eldorado 1999

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 1999 🢒 Eldorado 🢒 Transmission/Transaxle 🢒 Automatic Transaxle - 4T80-E 🢒 DTC P0748 Pressure Control Solenoid Circuit Electrical

Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

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 commanded current draw that differs from the actual current draw by more than a calibrated value, then DTC P0748 sets. DTC P0748 is a Type C DTC.

Conditions for Running the DTC

•	No Incorrect Gear Ratio DTC P0730.

•	No Maximum Adapt and Long Shift DTC P1811.

•	The system voltage is 10-17 volts.

•	The engine run time is greater than 1 second.

Conditions for Setting the DTC

The difference between the commanded PC solenoid valve current and the actual PC solenoid valve current is 0.05 amps or greater, for 2 seconds.

Action Taken When the DTC Sets

•	The PCM does not illuminate the malfunction indicator lamp (MIL).

•	SERVICE VEHICLE SOON, SERVICE TRANSMISSION displays on the driver information center (DIC).

•	The PCM commands maximum line pressure.

•	The PCM freezes steady state adapts.

•	The PCM freezes upshift adapts.

•	The PCM freezes garage shift adapts.

•	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.

•	The commanded PC solenoid valve current and the actual PC solenoid valve current are within 0.05 amps of each other for 2 seconds.

•	A scan tool can clear 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 the wiring at the PCM, the transmission 20-way connector, and the PC solenoid valve connector for the following conditions:

-	A backed out terminal

-	A damaged terminal

-	Reduced terminal tension

-	A chafed wire

-	A broken wire inside the insulation

-	Moisture intrusion

•	When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.

Test Description

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

This step verifies that the PCM responds to scan tool commands, and that the DTC could set intermittently.

This step verifies that the resistance value is within specifications. Use the J 35616-A connector test adapter kit, in order to avoid damaging the terminals.

DTC P0748 Pressure Control Solenoid Circuit Electrical

Step

Action

Value(s)

Yes

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

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Install the Scan Tool .
Turn the ignition switch to the RUN position.

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.

Record the Failure Records.
Clear the DTCs.
Start the engine.
Using the scan tool, increase and decrease the PC solenoid valve amperage.

Does the actual PC solenoid valve reading differ from the commanded PC solenoid valve reading by more than the specified amount?

0.05 amp

Go to Step 3

Go to Diagnostic Aids

Turn the ignition switch OFF.
Disconnect the transmission 20-way connector.
Install the J 39775 jumper harness to the transmission side of the 20-way connector.
Using the J 35616-A connector test adapter kit, connect the J 39200 digital multimeter (DMM) from terminal C to terminal D, and measure the resistance.

Is the PC solenoid valve resistance within the specified range?

3-8 ohms

Go to Step 7

Go to Step 4

Is the resistance greater than the specified value?

8 ohms

Go to Step 5

Go to Step 6

Inspect circuit 1228 of the automatic transmission wiring harness for an open.
Inspect circuit 1229 of the automatic transmission wiring harness for an open.

Refer to General Electrical Diagnosis in Wiring Systems.

Was a condition found?

Go to Step 9

Go to Step 10

Inspect circuits 1228 and 1229 of the automatic transmission wiring harness for a short together.

Refer to General Electrical Diagnosis in Wiring Systems.

Was the condition found?

Go to Step 9

Go to Step 10

Measure the resistance from terminal D to the transmission case.

Is the resistance less than the specified value?

10 ohms

Go to Step 8

Go to Step 11

Inspect circuit 1228 of the automatic transmission wiring harness for a short to ground.
Inspect circuit 1229 of the automatic transmission wiring harness for a short to ground.

Refer to General Electrical Diagnosis in Wiring Systems.

Was a condition found?

Go to Step 9

Go to Step 10

Replace the automatic transmission wiring harness.

Refer to Unit Repair.

Is the replacement complete?

Go to Step 16

Replace the PC solenoid valve.

Refer to Unit Repair.

Is the replacement complete?

Go to Step 16

Disconnect the J 39775 from the transmission side of the 20-way connector.
Reconnect the transmission 20-way connector.
Disconnect PCM connector C1.
Using the J 35616-A , connect the J 39200 DMM from terminal 38 of the PCM connector to a known good ground, and measure the resistance.

Is the resistance greater than the specified value?

10 ohms

Go to Step 12

Go to Step 13