OBD-II trouble code
P0778: Pressure Control Solenoid "B" Electrical
The transmission control module has detected an electrical fault in the circuit for pressure control solenoid B — an open, short, or out-of-range resistance. Expect shift-quality problems and possibly limp mode.
Quick facts
- System
- Powertrain
- Category
- Transmission / Pressure Control
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $150 – $800
- DIY difficulty
- Shop recommended
What does P0778 mean?
P0778 is the electrical-fault code for pressure control solenoid "B." It sets when the transmission control module (TCM) or PCM sees the solenoid's electrical circuit fall outside its normal range — an open, a short to power or ground, or resistance that doesn't match specification. Unlike the performance codes, which describe hydraulic behavior, P0778 is squarely about the electrical side: the module either can't drive the solenoid or is reading a current it doesn't expect.
Pressure control solenoid B is one of the transmission's variable-force solenoids that regulate hydraulic pressure to control shift feel and clutch apply. When its circuit faults electrically, the module can't accurately meter that pressure, so shifts come out harsh, delayed, or wrong, and many transmissions drop into a limp or failsafe mode that locks the gearbox in a single gear to protect it.
The usual causes are electrical rather than mechanical: a damaged or corroded connector at the transmission, chafed or broken wiring in the harness, a failed solenoid coil, or occasionally an internal harness problem where the wiring passes through the case. Because it's an electrical code, diagnosis starts with the connector and wiring and a resistance check of the solenoid — not with a fluid change. That said, contaminated fluid can shorten a solenoid's life, so fluid condition is still worth noting during the repair.
Common causes
- Corroded, loose, or damaged transmission connector
- Chafed, broken, or shorted wiring in the solenoid circuit
- Failed pressure control solenoid B coil (open or shorted)
- Damaged internal transmission wiring harness or pass-through connector
- Poor ground or voltage supply to the transmission control circuit
- Contaminated fluid that has degraded the solenoid over time
Symptoms
- Check engine light on with P0778 stored
- Harsh, delayed, or erratic shifts
- Transmission stuck in a single gear (limp mode)
- Slipping or flaring between shifts
- Transmission running warm
- Reduced fuel economy
Diagnostic steps
- 1.Scan for all transmission codes; a stored P0700 confirms the TCM has logged faults and pulls freeze-frame data.
- 2.Inspect the transmission connector and external harness for corrosion, damage, and backed-out pins.
- 3.Resistance-check pressure control solenoid B against the manufacturer's spec — an open or shorted reading confirms an electrical fault.
- 4.Check for continuity and shorts to power or ground along the solenoid wiring back to the module.
- 5.Verify the module's power and ground supplies are solid, since a bad ground can mimic a solenoid fault.
- 6.If the external circuit is good but the solenoid reads out of spec internally, the solenoid or internal harness is the likely fault.
Repair cost
$150 – $800
A wiring or connector repair can be as little as $100-$300 when the fault is external. Replacing pressure control solenoid B typically runs $250-$700 depending on whether the pan or valve body has to come down. If the internal case harness is at fault, labor climbs. Diagnostic time to isolate an electrical fault is money well spent before replacing parts.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with transmission shift solenoid replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.