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P0748 is an electrical fault in the line pressure (EPC) solenoid. The EPC solenoid controls overall transmission line pressure. When the PCM detects an open, short, or wrong resistance, it sets P0748 and usually defaults to maximum pressure (which causes harsh shifts) or limp mode. The solenoid is internal - pan must come off. On Ford 6F35, GM 6L80, and Chrysler 62TE this is one of the most common transmission codes after 100k miles. See top-rated scanners on Amazon ↑
These are statistical causes across ALL vehicles - your exact car may rank differently
For example, on a Honda 4-cyl the downstream O2 sensor causes P0748 64% of the time, but on a GM 5.3L V8 the catalytic converter is the cause 71% of the time. Get a probability ranking built specifically for your year, make, model, and mileage.
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🎯 Top Causes & Probability
60%
#1 - Most Likely
Failed EPC Solenoid
The line pressure solenoid coil has shorted or opened internally. Standalone replacement is possible on some transmissions; many require replacing the entire solenoid pack. Pan must come down regardless. Service the fluid at the same time.
🔧 Part
$60–$350
👨🔧 Labor
$220–$550
⚡ DIY
Hard
25%
#2 - Check First
Wiring or Connector Fault
Internal trans wiring harness, the case pass-through connector, or the external connector to the PCM has corroded or chafed. ATF intrusion is the #1 culprit at the case connector. Inspect and clean before condemning the solenoid.
🔧 Part
$15–$80
👨🔧 Labor
$120–$280
⚡ DIY
Medium
15%
#3 - Less Common
PCM / TCM Driver Failure
Less common but possible: the controller's solenoid driver circuit has failed. Test by checking solenoid resistance to spec at the harness end - if good, the controller is suspect. Usually requires a remanufactured PCM/TCM.
🔧 Part
$200–$800
👨🔧 Labor
$100–$300
⚡ DIY
Medium
🚗 Most Affected Vehicles
🛈 Is It Safe to Drive with P0748?
Generally no - P0748 typically forces limp mode or maximum line pressure, which means harsh, jarring shifts and reduced fuel economy. The trans isn't about to fail catastrophically tomorrow, but the high-pressure mode wears clutches and seals. Drive home or to a shop, then leave it until repaired. Solenoid replacement is one of the cheaper internal trans fixes - often $500–$900 - so don't put it off.
🔧 Step-by-Step Diagnosis
- Read all trans codes together - P0748 alone vs P0748 + P0775 + P0700 etc tells the story. Multiple solenoid electrical codes often = internal harness or full solenoid pack.
- Resistance test the solenoid - With the trans connector unplugged, ohm to the EPC solenoid pins per FSM. Most read 4–7 Ω. Open or shorted = bad solenoid (or internal harness).
- Inspect the case connector - Look for ATF intrusion, pushed-out pins, or corrosion. Clean and re-test before pan drop.
- Drop the pan and inspect - Look at debris in the magnet and filter. Heavy clutch material may indicate a bigger issue beyond the solenoid.
- Replace solenoid (or full pack) and refill - Use OEM-quality solenoid, new pan gasket and filter, and the correct ATF spec. Wrong fluid = repeat failure.
📍 Find a Trusted Shop Near You
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Tips for Choosing a Shop
- Use a transmission specialist for any solenoid pack replacement
- Ask whether they'll test the harness before pulling the pan
- Request a written estimate - expect $500–$900 for solenoid only
- Confirm they'll use the correct OEM ATF spec