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Home / DTC / B122B — right rear bank of the fan speed sensor

B122B — right rear bank of the fan speed sensor

Detailed page for trouble code B122B.

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Code

B122B

LAND ROVER B — Body

right rear bank of the fan speed sensor

Brand: LAND ROVER
Type: B — Body
Views: UK: 0 EN: 9 RU: 7
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Page language: EN

Causes

  • Damaged or corroded connector at the right-rear fan speed sensor
  • Broken, shorted or chafed wiring in the fan sensor circuit
  • Failed right-rear fan speed sensor (Hall-effect or frequency sensor)
  • Failed fan motor or internal fan control module
  • Poor ground or power supply to the sensor
  • Water intrusion or foreign debris in fan assembly

Symptoms

  • Cooling fan(s) not operating as expected (no run, runs only at full speed, or intermittent)
  • Engine temperature higher than normal or occasional overheating
  • Reduced HVAC cooling performance at low speeds
  • Check Engine / warning light or other message regarding cooling/fans
  • Stored or repeating fan-related DTCs

What to check

  • Safety first: park on level ground, set parking brake, allow engine and fans to cool, and isolate power before unplugging connectors.
  • Visually inspect the right-rear fan assembly, connector and wiring for corrosion, damage, or signs of water ingress.
  • Check fuses and fan relays related to the right-rear fan circuit.
  • With ignition ON (engine off) measure reference voltage at the sensor connector (see signal params).
  • Verify good ground continuity between sensor ground pin and chassis.
  • Scan tool: read freeze frame and live data for fan speed sensor and related fan commands; clear codes and attempt to re-create.

Signal parameters

  • Reference supply: typically 5 V (±0.5 V) or switched 12 V depending on sensor type — verify with factory wiring diagram.
  • Signal type: pulse/square-wave or frequency output proportional to fan RPM (0 V or 0 Hz when stopped, rising pulse frequency/0–5 V amplitude as speed increases).
  • Typical frequency range: 0 Hz at rest up to several hundred Hz at high fan speed (manufacturer-specific; commonly up to ~500–1000 Hz).
  • Expected signal voltage amplitude: approx. 0–5 V for Hall/frequency sensors; sensor should not be constant 0 V or constant battery voltage.
  • Ground: low resistance path to chassis ground (very low ohms).
  • Resistance checks: some sensors include internal electronics—refer to OEM specs. An open circuit or direct short to ground/power indicates failure.

Diagnostic algorithm

  1. Retrieve all related codes and live data using a calibrated scan tool. Note freeze-frame data and whether the fault is current or historic.
  2. Visually inspect connector, pins and harness for corrosion, bent pins, crushed sections or exposed conductors. Repair as required.
  3. With connector connected, backprobe the reference, signal and ground pins. Confirm correct reference voltage and ground. If missing, trace back to fuse/relay/BECM.
  4. Command fan ON using scan tool and observe the sensor signal with an oscilloscope or frequency-capable multimeter. Verify signal changes with commanded speed.
  5. If no signal or erratic signal, disconnect sensor and check for short to power/ground on the harness side. Repair wiring faults before replacing sensor.
  6. If harness is good and proper reference and ground are present, replace the right-rear fan speed sensor or the complete fan module depending on sensor integration.
  7. After repair, clear codes and perform function checks: command fans across speeds and verify correct sensor output and that the code does not return.
  8. If issue persists and wiring and sensor are confirmed good, consult wiring diagrams and consider module-level diagnostics (fan driver/BCM/IPC).

Likely causes

  • Connector corrosion / poor pin contact at the fan speed sensor
  • Open or short in harness between sensor and control module (most common)
  • Defective fan speed sensor or integrated fan electronics
  • Failed fan motor or fan driver circuit
  • Intermittent wiring caused by harness routing or rubbing

Fault status

⚠️ Status
B122B — Right rear fan speed sensor/circuit: signal out of range, intermittent, open or short detected by control module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

B122A B122C B1280 P0480 P0483 B12A1
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