P0748
Pressure Control Solenoid A Electrical.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 7
- AreaTransmission
- 48
- FaultThe specific fault in that area
What it means
P0748 means the transmission control unit has detected an electrical fault in the circuit of pressure control solenoid A, which regulates hydraulic line pressure in the automatic gearbox. The control unit saw a circuit voltage or current that did not match what it commanded, such as an open circuit, short circuit or incorrect resistance. Which gearbox solenoid is 'A' and how it is wired depends on the model and transmission.
Symptoms
- Harsh or delayed gear changes
- Slipping or flaring between gears
- Gearbox stuck in limp mode or a single gear
- Gearbox warning light or malfunction indicator lamp on
- Poor fuel economy or sluggish acceleration
- Gearbox overheating in some cases
Possible causes
- Faulty pressure control solenoid A (internal open or short circuit, or resistance out of specification)likely
- Damaged, chafed or corroded wiring between the solenoid and the transmission control unitlikely
- Poor connection at the gearbox internal harness connector or the control unit plug, including corrosion or bent pinslikely
- Contaminated, degraded or incorrect transmission fluid, or fluid ingress into the wiring connector, damaging the solenoid or its circuitpossible
- Low or unstable battery or system voltage affecting solenoid operationpossible
- Faulty transmission control unit or driver circuitrare
- Outdated control unit software where a known fault for that model is documentedrare
How to diagnose
- Read all stored codes and freeze frame data, noting gearbox temperature, speed and voltage when the fault set, and check for related codes
- Check the battery condition and charging voltage, as low voltage can set solenoid circuit faults
- Check the transmission fluid level, condition and smell, following the manufacturer's procedure for that model
- Inspect the external wiring and connectors to the gearbox and control unit for chafing, corrosion, heat damage and fluid contamination
- Measure the solenoid resistance at the gearbox connector and compare it with the manufacturer's specification for that transmission
- Check the circuit for continuity, short to earth and short to supply between the solenoid and the control unit
- Command the solenoid with a suitable diagnostic scan function if available and watch the current or response
- Check for applicable service bulletins or software updates for that model before condemning the control unit
How to fix
- Replace the pressure control solenoid A or the solenoid pack, as the model design requires
- Repair or replace damaged wiring and terminals, and secure the harness away from heat and abrasion
- Clean, repair or replace corroded or contaminated connectors, including the gearbox-side connector
- Change the transmission fluid and filter to the correct specification if contaminated, then check for further damage
- Repair charging or battery faults that cause unstable voltage
- Replace or reprogram the transmission control unit only after confirming it is faulty, or update its software where a known fault exists
Can I keep driving?
The car can usually be driven carefully for a short time, but the gearbox may be in limp mode and incorrect line pressure can cause slipping and wear. Book a repair soon and avoid heavy loads or towing until it is fixed.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.