P0778

Code

Generic P — Powertrain

Pressure Control Solenoid B Electrical

Brand: Generic

Type: P — Powertrain

Views: UK: 33 EN: 49 RU: 49

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Page language: EN

Causes

Open or short in solenoid B wiring (harness damage, chafed insulation)
Loose, corroded or water-intruded connector at solenoid or PCM/TCM
Failed pressure control solenoid B (coil open/short or internal short)
Faulty PCM/TCM driver or internal module fault
Low system/battery voltage or poor ground
Blown fuse or faulty power/ground distribution to transmission control circuits

Symptoms

Check Engine/Transmission MIL illuminated
HARSH, DELAYED, or ERRATIC shifts
Transmission stuck in 2nd/limp mode or reduced gear range
Unusual transmission noise or lack of proper line pressure
Transmission slip or inability to fully engage gears
Additional transmission-related codes present

What to check

Retrieve freeze frame, freeze data and full code list with scan tool; record PID values.
Visual inspection of connector, wiring harness, and PCM/TCM pins for corrosion, damage or looseness.
Verify battery voltage and good engine/transmission grounds with engine running and key on.
Check relevant fuses/relays and power supply to transmission connectors.
Measure solenoid coil resistance and compare to manufacturer spec or typical range.
Backprobe connector to observe commanded duty cycle and actual voltage while operating with a scan tool.

Signal parameters

Solenoid coil DC resistance: typically low (example range ~5–30 ohms) — varies by vehicle; consult OEM spec.
Control signal: PWM duty cycle commanded by PCM/TCM (0–100% duty) to modulate pressure.
Supply voltage at solenoid connector: near battery voltage (~12V) when circuit inactive; coil switched to ground by controller.
Control frequency: PWM frequency typically in the tens to low hundreds of Hz (varies by design).
Expected behavior: when commanded ON (higher duty), measured voltage waveform should show PWM pulses and coil current; when OFF, no continuous ground/short should be present.

Diagnostic algorithm

Connect a capable scan tool, record all transmission codes and live data (PC solenoid B commanded vs actual). Note freeze frame values.
Perform a thorough visual inspection of solenoid B connector, harness, and PCM/TCM connector. Repair obvious damage or corrosion.
Verify battery voltage (key ON, engine running) >12V and check engine/transmission grounds for low resistance.
With ignition ON (engine off) disconnect connector and measure solenoid coil DC resistance to ground across its terminals; compare to OEM spec. Replace solenoid if open or shorted.
Reconnect, backprobe solenoid connector and monitor voltage while commanding solenoid with scan tool (or during road test). Look for proper PWM duty, stable supply voltage, and switching to ground.
If no PWM or incorrect voltage, trace wiring for open/short to ground or battery. Check continuity from solenoid connector to PCM/TCM and for shorts to ground/battery.
Repair wiring or connector faults. If wiring and solenoid test good but fault persists, consider PCM/TCM driver failure — verify with manufacturer diagnostic procedures before replacing module.
After repairs, clear codes and perform a road test while monitoring PIDs. Confirm code does not return and transmission shifts properly.

Likely causes

Connector corrosion or poor pin contact at transmission solenoid connector
Broken wire or intermittent connection in harness to solenoid B
Solenoid coil failure (open/short or intermittent winding)
Low battery voltage during operation or poor engine/transmission ground
PCM/TCM driver transistor failure (less common than wiring/solenoid faults)

Fault status

⚠️ Status

Electrical fault detected in Pressure Control Solenoid B circuit — possible open, short to ground/voltage, intermittent connection, or control driver failure. May cause incorrect line pressure and transmission shift issues.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours