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Home / DTC / B12FB — Control of the hydraulic steering solenoid B

B12FB — Control of the hydraulic steering solenoid B

Detailed page for trouble code B12FB.

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B12FB

LAND ROVER B — Body

Control of the hydraulic steering solenoid B

Brand: LAND ROVER
Type: B — Body
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Page language: EN

Causes

  • Open or short in the wiring to steering solenoid B
  • Corroded, loose or damaged connector at the solenoid or ECU
  • Failed steering solenoid (coil open, shorted, or intermittent)
  • Faulty steering control module / ECU driver transistor
  • Low or unstable battery/charging system voltage
  • Blown fuse or faulty relay in the power/ground feed

Symptoms

  • Electric/ hydraulic power steering assist reduced or lost
  • Steering warning lamp or EPS light illuminated
  • Intermittent steering assist or jerky/variable steering feel
  • Stored multiple steering-related DTCs
  • Vehicle may enter reduced-assist / limp steering mode
  • Noise from steering unit (clicking) during assist changes

What to check

  • Read stored and pending DTCs and freeze-frame data with a diagnostic tool; record live data while reproducing the fault
  • Check battery voltage and charging system before testing (should be ~12.4–14.5 V)
  • Visually inspect solenoid B connector and wiring for corrosion, damage, pin push-out, or water entry
  • Check fuses and relays for power feed to the steering system
  • Backprobe solenoid connector and monitor supply, ground and control signal while operating steering
  • Measure coil resistance of solenoid B with connector disconnected

Signal parameters

  • Control: typically a PWM drive from the steering control module; duty cycle varies with assist demand (0–100%)
  • Control voltage range: 0–approx. 12 V PWM (model dependent); no drive should be present with ignition off
  • PWM frequency: commonly 50–2000 Hz depending on system (consult vehicle-specific data)
  • Coil resistance (typical): approximately 1–20 Ω depending on solenoid design — consult vehicle spec for exact value
  • Supply voltage at connector with ignition ON: battery voltage (~11.5–14.5 V)
  • Expected behavior: control line duty changes with steering input; no short to battery or ground

Diagnostic algorithm

  1. Connect a capable scan tool, read all steering and network codes, capture freeze-frame and live data for solenoid B while reproducing the symptom.
  2. Verify battery voltage and health. Poor supply can cause spurious DTCs — repair charging/battery issues first.
  3. Visually inspect the solenoid B connector and harness for damage, corrosion, water ingress or pin push-out. Repair any damage found.
  4. With ignition OFF, disconnect the solenoid connector and measure coil resistance across the solenoid terminals. Compare to vehicle-specific specification. Replace solenoid if out of range or open/shorted.
  5. With connector reconnected, backprobe the control and supply pins. With ignition ON and steering operated, observe supply voltage, ground continuity and control signal (PWM duty/frequency).
  6. If supply or ground is missing, trace/repair power feed, fuses, or ground. If control line is constant full voltage or shorted to ground, suspect ECU driver fault.
  7. Perform a wiggle test on the harness and connectors while monitoring live data / DTC status to find intermittent faults.
  8. If wiring and connector tests pass but solenoid does not respond to a known-good control signal, isolate and bench-test or replace the solenoid.
  9. If the solenoid and wiring are good, investigate the steering control module/ECU (check for software updates, reflash if specified, or replace unit following manufacturer procedures).
  10. Clear codes, perform a road/functional test to confirm repair, and re-scan for reappearance of DTC.

Likely causes

  • Damaged or corroded connector at solenoid B
  • Open or short in the harness between ECU and solenoid
  • Failed solenoid coil (open or short)
  • Intermittent ground or supply at the solenoid
  • ECU driver fault (less common than wiring/solenoid faults)

Fault status

⚠️ Status
Steering solenoid B control circuit fault. Inspect wiring, connector and solenoid; may cause reduced steering assist.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

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320

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