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Home / DTC / P0778 — Electric Pressure Control Solenoid B

P0778 — Electric Pressure Control Solenoid B

Detailed page for trouble code P0778.

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Code

P0778

LAND ROVER P — Powertrain

Electric Pressure Control Solenoid B

Brand: LAND ROVER
Type: P — Powertrain
AI status
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Page language: EN

Causes

  • Open, short or high resistance in solenoid B wiring or connector
  • Corroded or loose connector pins at the solenoid or TCM
  • Faulty pressure control solenoid B (stuck or electrically failed)
  • Contaminated or low/old transmission fluid causing solenoid valve sticking
  • Blown fuse, faulty relay or poor ground related to transmission circuits
  • Internal valve body or hydraulic faults affecting pressure control

Symptoms

  • Check Engine / Transmission warning lamp illuminated
  • Harsh, delayed, erratic or missing shifts
  • Transmission stuck in limp or reduced-gear mode
  • Poor driveability or reduced fuel economy
  • Unusual transmission noise or harsh engagement from a stop

What to check

  • Read and record freeze-frame and pending codes; clear code and re-run drive cycle to verify repeat
  • Inspect transmission fluid level and condition (smell, color, presence of debris)
  • Visually inspect wiring harness and connector for damage, corrosion, water ingress and secure connections
  • Check for blown fuses and proper grounds related to transmission control circuits
  • Backprobe solenoid connector and measure voltage and signal while commanding with a scan tool
  • Measure solenoid coil resistance and compare to factory specification

Signal parameters

  • Solenoid coil resistance (typical): ~7–25 ohms (vehicle-specific; consult Land Rover spec)
  • Command signal: PWM voltage from 0–12 V (duty cycle varies 0–100%)
  • Control frequency: commonly 50–300 Hz depending on system
  • Current draw when energized: typically 0.3–2 A depending on design
  • Expected scan-tool values: commanded duty changes should produce corresponding current/pressure response

Diagnostic algorithm

  1. Verify: Connect a capable diagnostic scanner, read DTCs and freeze-frame. Note any related transmission or electrical codes.
  2. Fluid check: Inspect transmission fluid level/condition. If fluid is low or contaminated, correct fluid and retest after clearing codes.
  3. Visual/wiring: Inspect harness and connector to solenoid B and at PCM/TCM for corrosion, bent pins, damage or pin push-out.
  4. Resistance test: With ignition OFF and connector disconnected, measure coil resistance between solenoid terminals. Compare to factory spec. An open or out-of-spec value indicates solenoid fault or harness problem.
  5. Power/ground test: With key ON (engine OFF) backprobe connector; verify proper reference voltage and ground. Command solenoid with scan tool and observe PWM/duty and voltage.
  6. Perform active test: Command solenoid ON/OFF with scanner while monitoring current or pressure response. Listen for solenoid activation (click).
  7. Pin-to-pin continuity/shorts: Check continuity from solenoid connector to TCM pins and check for short to battery or ground.
  8. Hydraulic verification: If electricals pass, use a transmission pressure gauge to confirm commanded line pressure changes correspond to solenoid commands. If pressure does not respond, suspect valve body or internal hydraulic fault.
  9. Repair: Repair wiring/connector or replace solenoid if confirmed faulty. Replace contaminated fluid and filter if required. After repair, clear codes and perform drive cycle to confirm no reoccurrence.
  10. If fault persists after replacing solenoid and repairing wiring, consider TCM/PCM diagnosis or valve body replacement per manufacturer guidance.

Likely causes

  • Damaged wiring harness to the solenoid (abrasion, rodent damage, connector corrosion)
  • Failed pressure control solenoid B
  • Dirty or degraded transmission fluid causing a sticking solenoid valve
  • Loose or corroded ground/connector at the solenoid
  • Intermittent connector contact or water ingress at connector

Fault status

⚠️ Status
P0778 — Electric Pressure Control Solenoid B: Electrical circuit or performance fault detected by transmission control. May cause incorrect line pressure and abnormal shifting or limp mode.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

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