P1242

Code

LAND ROVER P — Powertrain

High input sensor power supply

Brand: LAND ROVER

Type: P — Powertrain

Views: UK: 9 EN: 23 RU: 19

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Page language: EN

Causes

Damaged or shorted sensor harness (short to battery/ignition feed)
Faulty sensor with internal short to supply
Poor or corroded connector or pin causing intermittent contact or voltage feed
Aftermarket accessory or incorrect wiring feeding sensor circuit
Faulty ground or power distribution causing elevated reference voltage
ECM/PCM internal fault or failed voltage regulator

Symptoms

MIL/check engine lamp illuminated
Stored DTC P1242 (High input sensor power supply) and possibly related sensor-specific codes
Poor running, hesitation, surging or unstable idle if affected sensor is critical
Intermittent faults that may change with engine running or connector movement
Vehicle may enter limp mode or derate depending on affected inputs

What to check

Read and record freeze frame and related DTCs using a capable scan tool
Inspect wiring and connectors on suspected sensor circuits for damage, corrosion, or aftermarket splices
Visually inspect and wiggle-test harness while observing live data and voltage readings
Measure battery voltage with engine off and running to confirm charging system health
Backprobe the sensor connector and measure the reference/power pin versus ground with a multimeter
Inspect nearby accessories or recent work for incorrect wiring ties or fused taps

Signal parameters

Typical sensor reference/power rail ≈ 5.0 V (nominal) — acceptable tolerance commonly ~4.7–5.3 V
High-fault threshold often >~5.5–6.0 V (varies by manufacturer) — measured voltage close to battery (≈12 V) indicates short to B+
Sensor signal range usually 0–5 V; sudden jump toward battery voltage indicates short to power
ECM ground should be ≤0.1–0.2 Ω from chassis ground; elevated ground can affect readings

Diagnostic algorithm

Retrieve all stored and pending codes and freeze-frame data; note correlated sensors and operating conditions
Visually inspect the wiring and connectors for the reported sensor circuits. Repair obvious chafing, pin damage, or corrosion
With ignition ON (engine off), backprobe the sensor reference/power pin and measure voltage. Compare to expected ~5 V. If high, isolate by disconnecting the sensor — check voltage at connector still high
If disconnecting the sensor removes the high voltage, test the sensor on a bench or substitute a known-good sensor to confirm a sensor fault
If voltage remains high with sensor disconnected, trace wiring toward the ECU. Check for short to B+ using continuity/resistance checks (with battery disconnected for resistance tests)
Inspect for aftermarket accessories or taps connected into the sensor or reference circuit and remove/relocate if present
Check related power/ground distribution and fuses; verify battery and charging system voltages are normal
If wiring and sensors check good, backprobe the ECU connector and verify the reference voltage at the ECU pins. If fault appears at ECU side, suspect ECU internal failure and consult technical service bulletins before replacing ECU
After repairs, clear codes, perform test drive and re-scan. Confirm fault does not return before concluding repair

Likely causes

Short to battery voltage at the sensor reference/power wire
Corroded connector pin pushing battery voltage into reference circuit
Failed sensor that pulls the reference rail above normal
Aftermarket audio/engine bay accessory incorrectly tied into sensor circuits
ECM voltage regulator or input driver failure (less common)

Fault status

⚠️ Status

ECM detected voltage above allowable range on an input sensor power/reference circuit (High input sensor power supply). Fault stored; related sensor data may be invalid.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5 - 4.0 hours

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P1242 — High input sensor power supply