P123B

Code

LAND ROVER P — Powertrain

turbocharger impulse correlation compressor - Sensor B

Brand: LAND ROVER

Type: P — Powertrain

Views: UK: 6 EN: 18 RU: 7

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Page language: EN

Causes

Open, short or intermittent wiring between Sensor B and the ECU
Poor connector contact, corrosion or water ingress at sensor/ECU connectors
Failed or degraded compressor/turbo speed (impulse) sensor B
Physical damage to the compressor wheel or sensor mounting (air/gas ingestion, foreign object damage)
Excessive shaft play or mechanical fault in turbocharger affecting sensor reading
Faulty ECU or software/calibration issue

Symptoms

Illuminated MIL / check engine lamp
Reduced engine power, limp mode or reduced boost available depending on ECU strategy
Intermittent loss of boost or irregular boost behavior
Poor drivability, hesitation or surging at certain engine speeds
Stored freeze-frame data or related boost/turbo codes

What to check

Connect a suitable OBD-II diagnostic tool; confirm P123B and check for additional codes
Capture live data: turbo/compressor speed (Sensor A and Sensor B), boost pressure, and related PIDs while revving the engine
Compare Sensor B waveform/frequency/voltage to Sensor A and to expected values across rpm range
Visually inspect sensor B, connector and harness for damage, corrosion, or oil ingress
Backprobe the sensor connector with engine running to verify signal(s) and reference/ground integrity
Perform continuity and resistance checks on wiring between the sensor and ECU with ignition off

Signal parameters

Signal type: pulse or AC voltage signal proportional to compressor/turbo speed (often a Hall-effect or variable reluctance / VR style)
Typical voltage amplitude: 0–5 V for Hall/active sensors; ±peak for VR sensors (dependent on turbo speed)
Frequency range: low Hz at idle up to several kHz at high turbo speeds (varies by engine/turbo design)
Reference: a good correlation (consistent ratio) between Sensor A and Sensor B expected across rpm/load
Common faults: intermittent pulses, missing pulses, excessive noise, DC offset or no signal

Diagnostic algorithm

Retrieve freeze-frame and all stored DTCs with a diagnostic scanner. Note conditions when the code set (rpm, load, temperature).
Clear codes and perform a test drive while monitoring live PIDs for Sensor A and Sensor B speed/impulse signals and boost behavior to attempt to reproduce.
If code returns, capture waveform data from both sensors simultaneously (oscilloscope preferred) to evaluate pulse shape, amplitude and correlation.
Visually inspect Sensor B connector, wiring harness and ECU connector. Repair any corrosion, bent pins or damaged insulation. Reseat connectors.
Backprobe and measure sensor supply (if active), ground and signal with engine operating. Verify proper reference voltage and stable ground.
Check continuity and resistance of wiring from sensor to ECU with ignition off. Repair any opens/shorts. Protect wiring from chafing or heat damage.
Inspect turbocharger compressor wheel and housing for foreign object damage, interference with sensor tip, or excessive shaft play. Replace turbo if mechanical damage present.
If wiring and mechanical inspection OK but the signal is noisy or incorrect, replace Sensor B and retest.
If replacement sensor does not correct the problem, inspect/replace wiring harness or consider ECU input circuitry fault; consult manufacturer diagnostic information and software updates.
After repairs, clear codes and confirm the fault does not return under the same operating conditions; road test and recheck live signals.

Likely causes

Damaged or corroded connector at the sensor (most common)
Broken or chafed wiring harness to the compressor speed sensor
Contaminated or damaged sensor face (oil, debris) preventing proper pulse generation
Mis-mounted or displaced sensor (air gap incorrect) after service or impact
Failed turbo internal bearing or damaged turbine/compressor that alters pulse pattern

Fault status

⚠️ Status

Fault stored when compressor impulse/speed signal from Turbo Sensor B fails to correlate with the reference signal. Code may be stored as active or intermittent depending on signal behavior and ECU strategy.

🔴 Repair difficulty: Hard

⏱️ Diagnostic time: 1-4 hours

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P123B — turbocharger impulse correlation compressor - Sensor B