P0748 Code: Pressure Control Solenoid 'A' Electrical (Harsh Shifts)

Is your car shifting so hard it feels like you're being kicked in the back? Or maybe it refuses to shift out of second gear, revving high while you crawl down the road?

When you scan the vehicle, you see code P0748. The technical definition is "Pressure Control Solenoid 'A' Electrical."

Hearing "transmission problem" usually makes people clutch their wallets, fearing a $3,000 rebuild. But take a deep breath. P0748 is often an electrical issue or a dirty solenoid, not necessarily a broken transmission.

Inside your transmission pan is a "Valve Body" (the brain). Those small cylinders are the Pressure Control Solenoids.

What Does the Pressure Control Solenoid Do?

Think of your automatic transmission like a hydraulic machine. It uses fluid pressure to clamp down on clutch packs and change gears.

The Pressure Control Solenoid (PCS) is an electronic valve that opens and closes to regulate this fluid pressure. The Transmission Control Module (TCM) sends it an electrical current to control how soft or firm the shifts should be.

Code P0748 means the TCM has detected that the electrical voltage or resistance going to Solenoid 'A' is out of range. It's essentially saying: "I'm trying to talk to the solenoid, but the connection is bad."

Symptoms of P0748

Harsh Shifting: Without pressure control, the transmission often defaults to "maximum pressure," causing it to slam into gear.
Limp Mode: The car may lock itself in 2nd or 3rd gear to prevent damage, limiting your speed.
Delayed Engagement: You put the car in 'Drive,' and it takes 2-3 seconds before it actually moves.

Checking automatic transmission fluid dipstick for dirty oil

Step 1 is always checking your transmission fluid. Is it bright red (good) or dark brown (bad)?

Why Did This Happen? (Common Causes)

Dirty Transmission Fluid: If your fluid is old and full of metal shavings, it can clog the tiny screens inside the solenoid, causing resistance issues.
Wiring Damage: The wiring harness that goes into the transmission sits in a harsh environment. Heat, vibration, or road debris can fray the wires.
Faulty Solenoid: The solenoid coil itself may have failed internally (open circuit).
TCM Failure: Rarely, the computer controlling the transmission is at fault.

Don't Just Guess—Read the Transmission Data

Replacing a solenoid often requires dropping the transmission pan (a messy job). Before you do that, confirm the electrical fault.

The iCarsoft CR Pro S can read Transmission Live Data. You can watch the "Desired Pressure" vs. "Actual Pressure" current. If the TCM commands the solenoid but nothing changes, you've confirmed the electrical failure.

View Transmission Tools

How to Diagnose P0748

1. Check the Fluid Level and Condition

Pull the transmission dipstick (if equipped). Is the fluid level low? Is it dark brown or smelling like burnt toast? Dirty fluid causes solenoids to stick.

Pro Tip: If the fluid is dirty, a simple "Drain and Fill" might clear the blockage and fix the code without replacing parts.

2. Inspect the External Wiring

Trace the wire harness from the transmission up to the computer. Look for connectors that are soaked in oil (oil intrusion interferes with electrical signals) or wires chewed by rodents.

3. Check Resistance (Ohm Test)

If you are comfortable with a multimeter, you can unplug the main transmission connector and measure the resistance of the pins for Solenoid 'A'. Compare the ohms to your factory service manual. If it reads "OL" (Open Loop) or 0 (Short), the solenoid or internal wiring is dead.

Mechanic inspecting transmission wiring harness underneath vehicle

Inspecting the external connector for oil leaks or corrosion is a crucial diagnosis step.

Frequently Asked Questions (FAQ)

Is it safe to drive with P0748?

No. While the engine runs fine, the harsh shifting puts immense stress on your transmission gears, mounts, and axles. Driving in "Limp Mode" for long periods can cause the transmission to overheat.

How much does it cost to fix?

It depends on the location of the solenoid.
Simple Fix (External Solenoid): $150 - $300.
Complex Fix (Internal Solenoid): Requires dropping the pan and replacing fluid/filter: $400 - $800.
Wiring Repair: $100 - $200.

Can I just change the fluid to fix it?

Sometimes. If the solenoid is just "sticky" from debris rather than electrically broken, a fluid change helps. However, if the internal coil of the solenoid is broken (an electrical "open"), fresh fluid won't fix it—you must replace the part.

Which one is Solenoid 'A'?

Transmission solenoids are often labeled A, B, C or 1, 2, 3. You will need a specific diagram for your car's make and model year to identify exactly which cylinder inside the transmission pan is "A".

Will P0748 clear itself?

Electrical transmission codes are "sticky." Even if the problem is intermittent, the TCM usually keeps the code in memory as a "History Code." You should use a scanner like the iCarsoft CR Pro S to clear it manually after repairs to reset the transmission's learning strategy.