Code
B122C
LAND ROVER
B — Body
left of the seat bank speed of fan sensor
Views:
UK: 2
EN: 10
RU: 6
AI status
Completed
Completed
100%
Causes
- Damaged or disconnected wiring between sensor and control module
- Corroded or loose connector at the fan motor/sensor
- Failed fan speed sensor (tachometer/encoder)
- Faulty seat blower motor (internal encoder failure)
- Defective body/seat control module or software fault
- Blower obstructed or mechanically seized
Symptoms
- Left seat ventilation/heater fan inoperative or runs at single speed
- Reduced or no seat cooling/ventilation on left seat
- Stored B122C fault and related seat HVAC warnings/messages
- Fan speed indicator behaves erratically or does not change with controls
- Occasional electrical smell or increased motor noise if damaged
What to check
- Read and record current and pending codes + freeze frame data
- Visual inspection of left seat underside: wiring, connectors, fuses
- Check for foreign objects obstructing the blower
- Check fuse(s) and seat module grounds for good connection
- Probe connector for reference voltage, ground and signal with key on
- Wiring continuity/resistance check between sensor and control module
Signal parameters
- Sensor typically provides a pulsed/tach signal proportional to fan speed (square wave)
- Reference supply commonly 5 V (or vehicle-specific); signal amplitude often 0–5 V; some designs use switched 12 V pulsed outputs — consult service manual
- Signal frequency increases with fan RPM (0 Hz at stopped → higher Hz at high speed)
- Good ground continuity required for accurate sensor readings
- Exact voltages and frequency ranges are vehicle-specific — verify with Land Rover service data
Diagnostic algorithm
- Confirm B122C using a compatible fault reader and clear codes; see if fault returns.
- Attempt to reproduce symptom: operate seat ventilation across all speeds and note behavior.
- Perform visual inspection under left seat: connectors, wiring harness chafing, debris in blower.
- Check related fuses and ground points for corrosion and secure mounting.
- With harness connected, backprobe sensor connector: verify reference voltage, ground, and presence of tach/pulse signal at multiple commanded speeds using a multimeter/scope.
- If no reference or ground, trace wiring back to control module and repair open/shorts; if reference present but no signal, suspect sensor/motor.
- If intermittent signal, wiggle-test harness and connectors to locate breaks or corrosion.
- If motor/encoder suspected, disconnect and bench-test fan assembly or replace left seat blower module with known good unit if available.
- If wiring and fan assembly check good, test or reprogram seat/body control module per OEM procedures or replace if confirmed faulty.
- After repair, clear codes and verify proper operation over a test period.
Likely causes
- Connector corrosion or pin damage at left seat fan
- Open/short in signal or reference wire
- Failed Hall-effect/tach sensor inside the fan motor
- Contaminants or debris restricting fan movement
- Intermittent ground connection
- Control module intermittent or failed
Fault status
Status
Left seat bank fan speed sensor circuit fault. Signal missing, implausible, or out of expected range — fan feedback not detected or inconsistent.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
Workshop Manuals
Repair manuals for LAND ROVER
3
Land Rover Defender 300Tdi — Workshop Manual (1996 model year)
Workshop ManualLand Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)
Workshop ManualLand Rover Range Rover — Electrical Library (LRL 0453ENG, 2002)
Workshop ManualYour experience will help others
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