P0748
PowertrainPressure Control Solenoid 'A' Electrical
You'll usually notice this one as the gearbox suddenly turning clumsy: jerky changes, a clunk when it shifts, or the box dropping into limp mode so you're stuck in third with no kickdown. What's actually happened is the transmission control module has spotted an electrical problem with pressure-control solenoid 'A'. That solenoid controls the hydraulic line pressure the gearbox uses to make clean shifts, so when its circuit goes open or short, the changes go to pot and the warning light comes on.
ⓘ Information only. This page provides general educational information about fault code P0748. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0748 mean?
P0748 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Pressure Control Solenoid 'A' Electrical.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Harsh or delayed gear changes, often a thump when it shifts
- • Gearbox slipping or briefly losing drive as it changes up or down
- • Box drops into limp mode, leaving you with one or two gears only
- • Engine revs climb but the car doesn't pull as it should
- • Transmission or engine management light on the dash
- • Gearbox running hotter than normal on a long motorway run
Possible causes
Causes commonly associated with P0748, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Solenoid coil itself gone open or short circuit. This is the most common reason the code says 'Electrical', the winding inside has failed
- 2. Old or burnt transmission fluid that has gummed up the solenoid or restricted the valve body. Common on cars that have never had a fluid service
- 3. Wiring or connector trouble at the gearbox, chafed looms, corroded pins, or water that has crept into the connector block
- 4. Poor earth or voltage drop from a tired battery or charging fault, which can make a healthy solenoid read as faulty
- 5. Internal wear shedding metal debris that jams the solenoid or blocks a hydraulic passage
- 6. Faulty transmission control module or corrupted adaptation data, the rarest cause and worth ruling out everything else first
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read the live solenoid data and freeze frame with a proper scan tool that talks to the TCM, not just a basic OBD reader. Compare the commanded pressure against actual on a short road test
- 2. Check the fluid level and condition. Pull the dipstick or check the level plug. Burnt, dark, or low fluid points you away from electrical and towards a service or internal wear
- 3. Back-probe the solenoid connector and measure resistance across the coil. Most are in the few-ohms range, so an open or near-zero reading tells you the solenoid is dead
- 4. Wiggle-test and inspect the harness and connector at the gearbox for corrosion, green pins, or moisture. Flex the loom while watching live data
- 5. Check battery voltage and the gearbox earth, a poor supply throws electrical solenoid codes that vanish once the real fault is sorted
- 6. If the wiring and supply check out and resistance is wrong, drop the pan and inspect for metal debris before condemning the valve body or TCM
Common questions about P0748
What's this likely to cost me to sort out? +
Depends entirely on what's actually wrong. If it's a corroded connector or chafed wire, an independent might have you out the door for £60 to £150. A solenoid replacement, where the part is bolted into the valve body and you need a fluid and filter change to go with it, typically lands somewhere around £250 to £600 at a good independent, more at a main dealer who'll charge book hours and OE parts. If it turns out the valve body or TCM needs doing, or there's metal in the pan from internal wear, you're into four figures and you should think hard about whether the car's worth it.
How do I know if it's the solenoid or just dirty fluid on my car? +
Pull the transmission fluid and look at it. If it's clean and red and the level's right, lean towards an electrical fault, so get the coil resistance measured and the connector checked. If the fluid's dark, smells burnt, or the box has done 80,000-plus miles with no service history, a fluid and filter change is the cheap first move and can clear a sticking solenoid. The clincher is the resistance test: a coil reading out of spec or open circuit is electrically dead and no amount of fresh fluid will save it.
Is there anything I can do myself before paying a garage? +
A couple of things. Unplug the gearbox connector, check for corrosion or water inside, give it a clean with contact cleaner and reseat it, that alone fixes the odd intermittent case. Make sure your battery and earths are healthy, because a weak supply can trigger this. Beyond that, the solenoids live inside the gearbox behind the pan, with hot fluid and a tight torque spec on refit, so unless you've a clean space, a torque wrench and the right fluid to hand, the actual replacement is best left to a garage.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →