P18A4

Code

LAND ROVER P — Powertrain

Motion position sensor - Power circuit

Brand: LAND ROVER

Type: P — Powertrain

Views: UK: 19 EN: 28 RU: 20

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Page language: EN

Causes

Blown or intermittent fuse for the sensor supply circuit
Open, corroded or damaged wiring or connector to the sensor (open circuit)
Short to ground or short to battery in the sensor power feed
Poor or missing ground at sensor or module
Failed motion position sensor (internal power/driver fault)
Faulty control module/power driver or software fault

Symptoms

Malfunction Indicator Lamp (MIL) or warning message illuminated
Diagnostic trouble code P18A4 stored in module
Loss or degradation of systems that use motion position input (e.g., stability/steering/air suspension-related features) depending on vehicle
Intermittent or no motion/position live data from the sensor via a scan tool
Possible limp-home behaviour for affected systems

What to check

Read stored codes and freeze frame with a diagnostic scanner; note related / pending codes
Visually inspect sensor connector and harness for corrosion, damage, pin push-out, water intrusion or repairs
Check relevant fuse(s) for continuity and proper seating
Verify battery voltage is within nominal range (engine off and cranking) before doing other checks
Backprobe the sensor connector with key ON (engine OFF) to measure reference/supply voltage and ground
Perform wiggle test of harness and connectors while monitoring live data or watching for code set

Signal parameters

Expected power/reference: typically a switched 5 V reference or a fused 12 V supply depending on sensor design — consult OEM wiring diagram for exact value and pinout
Expected ground: < 0.2 ohm continuity to chassis ground (verify with meter)
Signal output: varies with position (0–5 V or centered around mid-rail depending on sensor type) — should change smoothly with motion
No-load current: small standby current; excessive current from supply may indicate internal short
If uncertain, obtain OEM pinout and voltage specs before replacing components

Diagnostic algorithm

Retrieve all stored/PENDING codes and live data from all modules; record freeze frame and related codes.
Visually inspect the sensor connector and wiring harness for damage, corrosion, rodent damage, or previous repair points.
Verify the proper fuse(s) for the sensor circuit(s); replace if blown and re-test. If fuse blows again, suspect short to battery.
With key ON engine OFF, backprobe sensor connector: measure supply/reference voltage and ground continuity. Compare to OEM spec. If no supply, trace back to fuse/relay/module.
Check for short to ground or battery: disconnect the sensor and measure resistance from the supply pin to ground and to battery. Very low resistance to ground indicates a short.
Wiggle harness and connectors while monitoring live data / watching for code set to identify intermittent faults.
If supply and ground are good at the connector but sensor has no proper output, substitute a known-good sensor or bench-test sensor if available.
If replacement sensor behaves the same, inspect/diagnose the supplying module (power driver) and its connectors/grounds and check for other module faults; consult manufacturer diagnostics for module-level tests.
After repair, clear codes and perform functional test / road test to verify the issue does not return. Re-scan for related codes.

Likely causes

Damaged connector or wiring (corrosion, chafing, broken wire) between module and sensor
Blown fuse or poor fuse connection on the sensor power feed
Sensor internal failure (power stage) or intermittent internal short
Poor ground at sensor or control module
Control module power output/driver fault (less common)

Fault status

⚠️ Status

P18A4 — Motion position sensor: Power circuit fault detected (open/short/abnormal voltage) in the sensor power supply circuit.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.0 hours

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P18A4 — Motion position sensor - Power circuit