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Home / DTC / P0799 — Control Solenoid intermittent C pressure

P0799 — Control Solenoid intermittent C pressure

Detailed page for trouble code P0799.

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P0799

LAND ROVER P — Powertrain

Control Solenoid intermittent C pressure

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

Causes

  • Intermittent open/short in solenoid C wiring or connector
  • Corroded, loose, or contaminated transmission connector
  • Failing or intermittent transmission pressure control solenoid (Solenoid C)
  • Poor ground or low battery/charging voltage during operation
  • Internal valve body fault or hydraulic leakage affecting pressure control
  • Faulty Transmission Control Module (TCM) or software glitch

Symptoms

  • Malfunction Indicator Lamp (MIL) or transmission warning lamp illuminated
  • Intermittent or harsh shifting, especially under load or at certain temperatures
  • Transmission may go into limp/limitation mode temporarily
  • Erratic line pressure, noticeable slipping or delayed engagement
  • Fault returns sporadically and may not be present at every drive cycle

What to check

  • Read and record freeze frame data and all stored transmission codes with a compatible scanner
  • Check live PID data for pressure control solenoid C command and feedback (duty cycle, ON/OFF) while driving or during actuator tests
  • Perform wiggle test on transmission harness and connector while monitoring for code set or signal dropouts
  • Visually inspect transmission connector for corrosion, bent pins, or water entry; inspect wiring for chafe, heat damage, or breaks
  • Measure solenoid C coil resistance at the connector (with harness disconnected) and compare to specification
  • Check battery and charging system voltage under load; low voltage can cause intermittent faults

Signal parameters

  • Typical solenoid coil resistance: ~5–30 ohms (model dependent) — consult vehicle-specific spec
  • Control signal: switched to ground by TCM or supplied pulse-width modulation (PWM) 0–12V depending on design
  • PWM duty cycle range: 0–100% (varies with requested line pressure)
  • Expected behavior: stable PWM or ON/OFF when commanded; no open circuit or intermittent voltage drop
  • Watch for transient voltage dips below ~8–10V during activation which can indicate power/ground issues (vehicle-specific thresholds vary)

Diagnostic algorithm

  1. Retrieve trouble codes and freeze-frame / live data. Note when the fault occurred (temperature, load, speed).
  2. Visually inspect the transmission connector, pins and wiring for corrosion, damage or loose pins. Repair any obvious issues.
  3. With ignition ON (engine off), disconnect harness and measure solenoid coil resistance at the transmission connector. Compare to factory spec. Replace solenoid if out of spec or intermittent when gently flexed.
  4. Backprobe the control wire at the connector and monitor voltage or PWM while commanding the solenoid ON/OFF with a scan tool. Look for stable, repeatable signal and correct voltage levels.
  5. Perform a wiggle test of the wiring harness between solenoid and TCM while monitoring live data or scoped trace to reproduce the intermittent condition. Repair any intermittent wiring faults found.
  6. Inspect and verify good battery/charging system voltage; check transmission ground(s) for low resistance to chassis/ battery negative.
  7. If wiring and connectors are good and solenoid resistance and bench activation are OK but intermittent persists, consider valve body/solenoid replacement (one or more solenoids) or TCM testing/reprogramming. Replace only after verifying component-level failure.
  8. After repairs, clear codes and road test under the same conditions to confirm fault does not return. Use high-resolution data logging or oscilloscope during test drive if necessary to verify signal stability.

Likely causes

  • Wiring chafe where harness flexes (intermittent contact)
  • Water ingress / corrosion at transmission harness connector
  • High resistance or intermittent connection at ground or power feed to the transmission
  • Solenoid coil heating and opening/closing intermittently as it ages
  • Intermittent TCM driver transistor or solder joint

Fault status

⚠️ Status
Intermittent fault detected on Transmission Pressure Control Solenoid C circuit. TCM flagged unstable or out-of-range control signal for Solenoid C; fault may be present intermittently and can cause erratic shifting or limp-in mode.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-4.0 hours

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302

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