B1866

Code

LAND ROVER B — Body

High ignition

Brand: LAND ROVER

Type: B — Body

Views: UK: 12 EN: 23 RU: 15

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Page language: EN

Causes

Overcharging from alternator/voltage regulator failure
Battery being charged externally (jump-starting, charger) while key on
Short to battery voltage (B+) on an ignition feed or harness
Faulty ignition switch or ignition feed relay
Poor or corroded ground causing voltage spikes
Intermittent/poor connector or wiring damage in ignition circuit

Symptoms

DTC B1866 stored in fault memory
Electrical/electronic module warnings or erratic behavior
Battery/charging system warning lamp may illuminate
Blown fuses related to ignition feed circuits
Unreliable ignition/accessory power or intermittent loss
Possible inability to start or unexpected shutdown in rare cases

What to check

Scan for additional DTCs and capture freeze-frame or live data
Inspect battery condition and terminal connections for corrosion/tightness
Measure battery voltage with key off, key on (engine off), and engine running
Check charging system voltage at idle and at ~2000 rpm
Visually inspect wiring and connectors on ignition feed, relays and modules
Inspect ground straps (battery to chassis, engine to chassis) for continuity and corrosion

Signal parameters

Battery voltage, key off: ~12.4–12.8 V (depends on state of charge)
Battery voltage, key on, engine off: ~12.4–13.0 V
Charging system voltage, engine running: typically 13.5–14.8 V
High-voltage threshold (fault trigger): generally >15.0–16.0 V (manufacturer-specific)
Cranking voltage should not drop below ~9–10 V under load
No ignition feed spikes or sustained voltages above charging spec

Diagnostic algorithm

Read and record all stored DTCs and freeze-frame data. Note any simultaneous codes.
Visually inspect battery, alternator, wiring harnesses, connectors, and grounds for damage or corrosion.
With a digital multimeter, measure battery voltage: key off, key on (engine off), and engine running at idle and ~2000 rpm. Compare to expected ranges.
If charging voltage is above specification, isolate and test alternator/regulator (bench test or scope alternator output).
If alternator OK, check ignition feed circuits for a short to B+ using wiring diagrams: disconnect connectors sectionally and monitor voltage to localize feed supplying excessive voltage.
Inspect and test ignition switch and feed relays for proper operation and absence of welded contacts causing constant B+.
Load-test the battery and inspect for voltage excursions using a scope if intermittent spikes are suspected.
Repair or replace any damaged wiring, connectors, relays, or faulty modules per workshop manual.
Clear codes and perform a drive/start cycle to verify the fault does not return. Re-scan for stored codes after repairs.

Likely causes

Alternator/regulator overvoltage condition
Short to B+ on ignition feed or related harness
Faulty ignition switch or relay sticking closed
Corroded/loose battery ground or engine ground strap
Recent battery charger or jump-start event introduced high voltage
Faulty body/control module input stage

Fault status

⚠️ Status

Control module has detected an ignition feed voltage higher than the allowed threshold. Investigate charging system, ignition feed wiring, connectors, grounds and related modules.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 3.0 hours

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