Code
B143F
LAND ROVER
B — Body
Compressor Control - High Side Circuit
Views:
UK: 2
EN: 8
RU: 3
AI status
Completed
Completed
100%
Causes
- Blown fuse or faulty high‑side relay/fuse for the compressor power feed
- Open, short to ground, or high resistance in the compressor power wiring/harness
- Corroded/loose connector at compressor or engine wiring harness
- Failed compressor clutch coil or internal compressor power electronics
- Faulty Body/Climate/Powertrain control module high‑side driver
- Intermittent battery/charging system low voltage during A/C command
Symptoms
- Air conditioning inoperative or intermittent (no cooling)
- Compressor does not engage when A/C is requested
- Related warning message or lamp on instrument cluster
- Possible blown fuse or relays that do not activate
- Erratic compressor operation or repeated trips/faults
What to check
- Read and record all stored fault codes and freeze frame data with a diagnostic scanner
- Verify battery voltage and charging system health (engine running and at rest)
- Inspect A/C-related fuses and relays; check for blown fuse(s)
- Visually inspect compressor wiring, connectors, and harness for damage, corrosion, or water
- Check for secondary codes that may indicate BCM or module communication problems
- Attempt to command the compressor on/off with a scan tool and observe outputs
Signal parameters
- Battery supply voltage to compressor circuit: ~11.5–14.5 V (vehicle dependent) when engine running
- Commanded high‑side voltage at compressor power terminal: near battery voltage when ON
- High‑side driver may use PWM; expected duty cycle and frequency are manufacturer-specific (commonly tens to hundreds of Hz)
- Compressor clutch coil resistance (if applicable): manufacturer-specific; typical range 0.5–10 ohms for clutch coils—refer to service data
- Continuity: low ohms between battery + fuse output and compressor power pin when wiring intact; open/infinite ohms indicate break
Diagnostic algorithm
- Safety: Park, apply parking brake, switch ignition OFF, disconnect battery only if required by repair procedures. Use PPE and follow battery/airbag precautions.
- Scan and reproduce: Use a capable scan tool. Read all codes, note freeze frame, clear codes, then attempt to command A/C on to re-create the fault while monitoring live data and outputs.
- Supply check: With ignition ON and A/C requested, measure battery voltage at the compressor power feed (fuse/relay output). Verify fused feed has battery voltage. If no voltage, inspect fuse/relay and upstream wiring.
- Relay/fuse test: Verify operation of compressor supply relay (listen/activate with scan tool or apply 12V). Swap with known-good relay if applicable.
- Connector and wiring inspection: Visually inspect and wiggle harnesses from fuse/relay to compressor. Back-probe at the compressor connector; check for corrosion, loose pins, or melted insulation. Perform continuity and resistance checks to the fuse/relay and ground.
- Measure driver output: Back-probe control/module output that drives the high-side transistor while commanding compressor ON. Expect near-battery voltage at the load. If module output present but voltage drops under load, suspect short or overcurrent in harness or compressor.
- Compressor coil test: With battery disconnected, measure coil resistance at compressor terminal(s). Compare to manufacturer specification. A shorted or open coil indicates compressor replacement.
- Short/overcurrent test: Check for short to ground on the power feed using an amp clamp or inline ammeter while commanding compressor. Excessive current indicates internal short at compressor or wiring fault.
- Module and grounding checks: Verify control module grounds and communications (CAN/BUS) are healthy. If module output not present and wiring OK, suspect module driver failure.
- Repair and verify: Repair/replace damaged wiring, connector, fuse, relay, compressor, or control module as indicated. Clear codes, retest multiple cycles and verify no recurrence.
- When replacing modules or compressor, follow manufacturer procedures for programming, initialization or adaptation if required.
Likely causes
- Blown A/C fuse or defective compressor power relay
- Open circuit or damaged insulation in positive supply feed to compressor
- High resistance at connector pins due to corrosion or poor mating
- Compressor clutch/coils have internal short or open winding
- Controller (BCM/CCM/PCM) high side transistor or MOSFET has failed
- Aftermarket accessories or repairs damaged the A/C supply circuit
Fault status
Status
DTC B143F indicates a fault on the A/C compressor high-side power circuit. The controller detected an abnormal condition (open, short, overcurrent, or loss of supply) while commanding the compressor.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
Workshop Manuals
Repair manuals for LAND ROVER
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Land Rover Defender 300Tdi — Workshop Manual (1996 model year)
Workshop Manual199,00 UAH
Land Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)
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Land Rover Range Rover — Electrical Library (LRL 0453ENG, 2002)
Workshop Manual199,00 UAH
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