P1240

Code

LAND ROVER P — Powertrain

Malfunctioning of the power supply of sensor

Brand: LAND ROVER

Type: P — Powertrain

Views: UK: 18 EN: 33 RU: 24

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Page language: EN

Causes

Blown fuse or fusible link supplying the sensor circuit
Open, shorted, or corroded wiring or connectors in the sensor power or ground circuit
Poor or intermittent ground at sensor or ECM/PCM
Faulty sensor with internal power supply/heater failure
Faulty PCM/ECM power driver or internal fault
Aftermarket modifications or damage (shorts, pinched wires)

Symptoms

Check Engine MIL illuminated with code P1240 stored
Intermittent or permanent loss of the related sensor signal
Rough idle, hesitation, poor drivability under certain conditions
Reduced fuel economy and increased emissions
Possible failure to start if a critical sensor is unpowered

What to check

Retrieve freeze frame and read supporting/related codes to identify which sensor circuit is affected
Visually inspect wiring harness and connectors for damage, corrosion, pinched wires, rodent damage, or water ingress
Check relevant fuses and fusible links for continuity
Back-probe sensor connector to measure supply voltage, reference voltage and ground continuity
Check battery voltage and chassis/engine grounds for proper connection and corrosion

Signal parameters

Primary supply voltage: ~12 V (battery voltage) at fused feed with ignition ON (exact value depends on circuit)
Reference voltage (if applicable): nominal 5.0 V ±0.25 V from PCM for many sensors
Ground continuity:
Sensor signal range: 0–5 V (varies by sensor type) — verify expected idle and active values from service data
Heater supply (for heated sensors): switched 12 V when commanded by PCM; continuity/ohms per manufacturer spec

Diagnostic algorithm

Record codes and freeze-frame data; identify which sensor circuit the PCM refers to using manufacturer wiring diagrams.
Visually inspect harness and connectors for the identified sensor. Repair any obvious damage or corrosion.
With key ON (engine off), verify fused power to the sensor connector. Replace blown fuse or repair circuit if absent.
Back-probe the sensor connector: measure reference voltage (≈5 V), battery feed (≈12 V where applicable), and ground continuity. Compare to expected values.
With engine running or with PCM commanding heater, check sensor signal and heater supply under operation. Observe for intermittent drops while moving harness to replicate fault.
If wiring and supply are good, measure sensor resistance/insulation per service manual. Replace sensor if out of spec.
If replacement sensor does not clear the issue, inspect PCM power/ground and driver outputs. Consult wiring diagrams and perform PCM bench tests or consider module replacement if confirmed faulty.
After repair, clear codes and perform test drive to confirm fault does not return.

Likely causes

Open or short in sensor power/ground wiring
Blown fuse or poor connector at power source
Corroded or loose sensor connector causing intermittent power
Failed sensor (internal power/heater element)

Fault status

⚠️ Status

Malfunction detected in the power supply circuit to a sensor. The PCM observed abnormal supply, reference, or ground conditions causing the sensor to operate improperly.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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P1240 — Malfunctioning of the power supply of sensor