P0748 OBD-II: Pressure Control Solenoid "A" Electrical

What Does P0748 Code Mean?

OBD-II Code P0748 is defined as a Pressure Control Solenoid Electrical

The purpose of the automatic transmission is to match the engine's optimum power and torque characteristics to the driver's desired rate of acceleration and speed by auto-selecting different gear ratios or 'speeds' to power the wheels. The Pressure Control Solenoid controls the hydraulic pressure in the transmission which is needed to apply the various clutch packs in the transmission that provide the different gear ratios needed to efficiently propel the vehicle down the roadways.

When the code P0748 is set in the Powertrain Computer, it means that the Powertrain Computer or PCM is not seeing the specified electrical voltage drops from the Pressure Control Solenoid as it performs its tasks.

P0748 Symptoms

• Check Engine Light may illuminate
• Vehicle will not shift from gear to gear properly
• Vehicle may not be driveable
• Decrease in fuel economy
• In unusual cases, there are no adverse conditions noticed by the driver
• In some cases, there may be performance problems

Common Problems That Trigger the P0748 Code

• Defective Pressure Solenoid
• Defective Pressure Solenoid wiring or connector
• Defective Valve Body
• Dirty transmission fluid that restricts the hydraulic passages

Common Misdiagnoses

• Engine misfire or performance problem
• Driveline problem

Polluting Gases Expelled

• HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
• CO (Carbon Monoxide): Partially burned fuel that is an odorless and deadly poisonous gas
• NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog

P0748 Diagnostic Theory for Shops and Technicians

When diagnosing a P0748 code, it is important to record the freeze frame information and then to duplicate the code setting conditions with a test drive at the freeze frame road speed. Start out from a dead stop and gently accelerate. Watch the scan data to see if the PCM is commanding the Pressure Control Solenoid. It will be displayed as a duty cycle i.e. in a percentage that rises and falls in value. If the PCM is commanding the Pressure Control Solenoid with a higher and higher duty cycle and the transmission is not performing correctly, then you may have located the problem. Next step is to start doing pinpoint tests i.e voltage drops and continuity tests of the Pressure Control Solenoid. I generally back probe the wiring harness so I don't have to disassemble the transmission. And, ALWAYS check the condition of the fluid. Is it dirty, brown and burnt or is it that clear cranberry color?