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Home / DTC / B1A91 — Speed Position Sensor A

B1A91 — Speed Position Sensor A

Detailed page for trouble code B1A91.

34,297codes
59brands
11,806generic
22,491specific
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Code

B1A91

LAND ROVER B — Body

Speed Position Sensor A

Brand: LAND ROVER
Type: B — Body
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty speed/position sensor (A)
  • Damaged wiring or connector (open, short to power/ground, or corrosion)
  • Poor ground or reference voltage to the sensor
  • Contaminated, magnetized, or damaged reluctor/target wheel or sensor face
  • Intermittent connector contact due to water/loose pin
  • Module/ECU communication fault or software anomaly

Symptoms

  • ABS, traction control or stability warning lamps may illuminate
  • Speedometer or odometer inaccurate or inoperative
  • Cruise control may be disabled
  • Transmission shifting irregularities or limp‑in mode on vehicles relying on speed input
  • Intermittent or no vehicle speed data in scan tool live data
  • Possible driveline noise or vibration if reluctor/target damaged

What to check

  • Retrieve freeze frame and full scan tool report; note related codes
  • Check live data for speed/position sensor A while rolling vehicle or rotating component by hand
  • Inspect sensor connector for corrosion, bent pins, water ingress or broken latches
  • Visually inspect reluctor/target wheel, tone ring, or sensor mounting for damage, missing teeth, or excessive gap
  • Wiggle harness and connectors while monitoring live data for intermittent changes
  • Check for related chassis (Cxxxx), powertrain (Pxxxx) or network (Uxxxx) codes that may indicate module or communication faults

Signal parameters

  • Hall/active sensor: square/pulsed signal 0–5 V (often referenced to 5 V or switched 12 V); frequency increases with speed
  • Variable reluctance (VR) sensor: AC sine waveform; amplitude typically 0.1–1.5 VAC (or higher at speed) and frequency proportional to speed
  • Typical idle/low speed frequency: low Hz; high speed: 100s Hz depending on sensor location and gear ratio
  • Expected steady waveform, no excessive noise, no dropouts; correct polarity for Hall sensors

Diagnostic algorithm

  1. Connect a capable scan tool and confirm B1A91 and any related codes; record live data while stationary and while driving at low speed.
  2. Visually inspect the sensor A, connector, wiring harness routing, and mounting. Repair obvious damage or corrosion.
  3. Backprobe the sensor connector: verify reference voltage (if applicable), ground continuity, and signal with ignition ON and while rotating the hub/shaft. Compare readings to signal_params.
  4. If VR sensor suspected, use multimeter AC volts while turning wheel; if Hall, check for 5 V ref and ground then check pulsed output with oscilloscope or DVOM (frequency/voltage).
  5. Wiggle harness and connectors while monitoring signal and codes to find intermittent faults.
  6. Inspect reluctor/tone ring for missing teeth, debris, or excessive air gap; measure gap to manufacturer spec and reposition or replace if out of spec.
  7. Check continuity from sensor connector to module pin to rule out wiring opens/shorts; repair any shorts to power/ground.
  8. If wiring and sensor tests pass, swap with a known good same‑type sensor (if possible) or substitute a new sensor and retest.
  9. After repair, clear codes and perform a road test to confirm stable signal and no reappearance of B1A91. If code returns, consider module or network diagnostics and perform manufacturer service bulletins/software checks.

Likely causes

  • Corroded/loose connector at the sensor
  • Broken or chafed harness between sensor and control module
  • Sensor failed from contamination or impact
  • Reluctor/target ring missing/misaligned/damaged

Fault status

⚠️ Status
Speed Position Sensor A — signal invalid, missing, or out of range. Inspect sensor A, wiring, connector, and tone/reluctor components.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B1A90 B1A92 C0035 C0040 P0500 U0121
320

Browse 320 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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