P1591

Code

LAND ROVER P — Powertrain

speed distance control signal Decrease

Brand: LAND ROVER

Type: P — Powertrain

Views: UK: 15 EN: 20 RU: 19

AI status

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Page language: EN

Causes

Obstructed, damaged or misaligned radar/laser sensor (front end sensor)
Faulty speed/distance control sensor/module
Open/short/poor connection in sensor power, ground or communication wiring
Loss or degradation of vehicle speed signal (wheel speed sensors or VSS)
CAN/LIN bus communication errors or module wake-up failure
Low system/battery voltage or blown fuse

Symptoms

Adaptive cruise/distance control disabled or reduced performance
Cruise control may disengage unexpectedly
Driver information message such as 'Service Adaptive Cruise' or similar
ABS/ESC or other related warnings (if vehicle speed input affected)
Loss of lane-keeping/assistance features on some models

What to check

Read stored and pending codes and freeze-frame data with a diagnostic tool
Visually inspect front radar/lidar sensor for damage, blockage or misalignment
Check for relevant warning messages on the dash and note conditions when code set
Inspect sensor connectors for corrosion, water ingress, bent pins and secure locking
Verify fuses and battery/charging system voltage under load
Scan CAN/LIN networks for communication errors and module presence

Signal parameters

Sensor supply voltage: approximately battery voltage (expected ~11–14.5 V when engine running)
Sensor logic/reference: many control sensors use 5 V reference (nominal ~4.8–5.2 V)
CAN bus idle voltages: CAN High/CAN Low nominal around 2.5 V each, differential when active (CAN High ~3.5 V, CAN Low ~1.5 V under dominant state)
Wheel speed sensor output: pulse/frequency proportional to wheel speed (check pulses per km/h with scan tool or oscilloscope)
Expected steady communications with ACC module when ignition on; look for intermittent drops or CRC errors

Diagnostic algorithm

Connect a full-feature scanner and record codes, freeze-frame, and live data related to ACC/radar and vehicle speed.
Visually inspect the front radar/lidar module: remove obstruction, clean lens, check mounting and alignment.
Inspect wiring and connectors at the radar sensor and associated modules. Repair any damaged wires/pins and ensure good grounds.
Verify power and ground at the sensor connector with a DMM (battery voltage present, ground
Monitor CAN bus and ACC module communication on the scanner. Look for missing module, intermittent comms or bus errors.
Check wheel speed sensors and tone rings for correct signal output (use oscilloscope or scanner wheel speed live data). Replace any faulty sensors.
Check related fuses and measure system voltage during test drive to rule out supply issues.
If hardware and wiring are good, check for available manufacturer software/ECU updates and perform module calibration/relearning per service manual.
After repairs, clear codes and verify the system operates correctly on road test; re-check for return of fault and run self-tests/calibration as required.

Likely causes

Contamination (dirt, ice, aftermarket accessory) blocking radar/lidar
Corroded connector at sensor or ABS module
Damaged wiring harness at radiator/apron area
Failed front radar/transceiver module
Intermittent wheel speed sensor or tone ring damage
ECM/BCM/ACC module fault or missing software calibration

Fault status

⚠️ Status

Speed/distance control signal decreased — the control module detected an abnormally low or dropped input from the speed/distance sensor or its communications. Adaptive distance/speed control may be disabled until fault is corrected.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5 - 4.0 hours

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Manual library for LAND ROVER

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Browse 413 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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