P0748 Code: Pressure Control Solenoid A Electrical

What the P0748 code means

Solenoids are electric valves that direct fluid pressure to the clutches and brakes inside the transmission. Pressure control solenoid A controls the line pressure that applies the clutches, and the firmness of the shifts depends on it. The transmission computer commands the solenoids and monitors both their electrical circuit and the result, meaning the input and output speeds of the transmission.

The P0748 code means there is an electrical fault in the solenoid: an open circuit, a short or a resistance out of range. It is an electrical fault: the wiring, the connector (very often the case pass-through connector, which leaks fluid), the solenoid itself or the control module.

On any transmission code, the first check is the fluid. Check the level with the manufacturer procedure (often with the engine running and at a specific temperature). The fluid should be red or pink and should not smell burnt. Low or worn-out fluid causes slipping, harsh shifts and solenoid or ratio codes that go away once it is corrected.

Always start with the simplest things: fuse, relay and connector. Then check the supply, ground and signal with the component connected (using back-probes), and finally the continuity of each wire to the computer. Only if all of that is good do you replace the component.

Read the P0700 guide to understand how transmission codes are read and why you need a scan tool that can talk to the transmission module.

P0748 code symptoms

• Check engine light or transmission warning light on.
• Harsh shifts, late shifts or shifts that do not happen.
• Limp mode: the transmission stays in one fixed gear (often 2nd, 3rd or 4th).
• Slipping or high rpm in certain gears.

Likely causes of the P0748 code

1. Transmission connector with fluid or corrosion. Very common at the case pass-through connector.
2. Damaged internal or external wiring from heat or rubbing.
3. Solenoid with an open or shorted coil. The resistance is out of specification.
4. Transmission control module. Uncommon.

How to diagnose the P0748 code step by step

1. Check the fluid level and condition using the manufacturer procedure.
2. Read all the codes in the transmission module with a scan tool that can reach it.
3. Measure the solenoid resistance at the transmission connector and compare it with the manual.
4. Check the insulation to ground. It should read infinite.
5. Command the solenoid with the scan tool and listen for the click.
6. Inspect the case connector. Look for fluid inside it or green pins.

How to fix the P0748 code

• Repair the connector or the wiring.
• Replace the solenoid (or the valve body if the solenoid is built in).
• Clear the adaptations and perform the relearn procedure.
• Clear the codes and verify with a road test.

Technical reference data

• Shift solenoids (on/off): roughly 10 to 30 ohms.
• Pressure or linear solenoids (PWM control): roughly 3 to 8 ohms.
• Normal transmission fluid temperature: 70 to 95 °C (158 to 203 °F).
• Reference values: check the manufacturer data for your vehicle.

Brand-specific notes

On many transmissions the solenoids sit in the valve body and you reach them by removing the pan. On some, the solenoids are sold only together with the valve body or with the built-in control module (a mechatronic unit). After you replace solenoids or the valve body, clearing the adaptations and doing a relearn with a scan tool is usually required.

P0748 on Aisin and Jatco

On many Aisin and Jatco transmissions the solenoids are in the valve body and are reached by removing the pan.

P0748 on GM

On the GM 6T transmissions the solenoids are in the valve body and are reached by removing the pan.

P0748 on Ford

On the Ford 6R transmissions the solenoids are in the valve body and are reached by removing the pan.

P0748 on Volkswagen

The Volkswagen DSG uses a mechatronic unit, and on many modern transmissions the solenoids come only with the valve body or with the integrated control module.

Frequently asked questions about P0748