U0142

Code

Generic U — Network/User

Lost Communication With Body Control Module B

Brand: Generic

Type: U — Network/User

Views: UK: 17 EN: 31 RU: 26

AI status

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Page language: EN

Causes

BCM B power supply fault (blown fuse, lost battery feed)
BCM B ground open or high resistance ground
Damaged or corroded BCM connector or pins
Broken or shorted CAN/LIN wiring between BCM B and network
Failed BCM B (hardware or internal firmware fault)
Network termination or bus wiring fault (open, short to battery/ground)

Symptoms

Malfunction indicator lamp (MIL) or network warning lamp may be on
Functions controlled by BCM B not available or intermittent (locks, interior lights, wipers, convenience functions depending on vehicle)
Scan tool reports U0142 and shows BCM B not present or unable to connect
Other modules report related communication trouble codes or bus-off conditions
Intermittent loss of multiple convenience systems
Vehicle may show gateway/module errors on dash

What to check

Connect a capable OBD-II scan tool and verify U0142 and any related U-codes; record freeze frame and module list
Verify battery voltage (≥12.4 V recommended) and note any recent battery disconnects
Check BCM B fuses and relays for continuity and proper operation
Visually inspect BCM connector for corrosion, bent pins, damage or water intrusion
Check chassis and engine grounds associated with BCM B for tightness and cleanliness
Inspect CAN wiring and harnesses for physical damage, rodent bites or pinched sections

Signal parameters

Typical CAN recessive voltages (idle): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (common-mode ~2.5 V)
Typical CAN dominant voltages: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
Differential voltage during active frames ≈ 1.5–2.5 V depending on network and transceivers
Bus termination resistance ≈ 60 ohms measured between CAN_H and CAN_L at vehicle end-to-end (two 120 Ω terminators in parallel)
BCM supply voltage (key on): ~12 V (vehicle-specific), ground resistance ideally
Network baud rate is vehicle-dependent (commonly 250 kbps or 500 kbps); verify correct speed before using analyzers

Diagnostic algorithm

Verify and record code(s): clear codes and attempt to reproduce; note whether U0142 returns and whether it is permanent or intermittent.
Confirm BCM presence: use scan tool to list modules; if BCM B not listed, proceed to electrical checks.
Check vehicle battery state and top-off if low; ensure stable power during tests.
Check fuses/relays feeding BCM B for continuity and correct supply voltage with key on and off.
Inspect BCM connector and harness for corrosion, bent pins, water ingress and repair or reseal as needed.
Verify BCM ground points are clean and tight; measure voltage drop while cranking/accessing loads if needed.
Measure CAN bus voltages at the BCM connector (backprobe): check recessive voltages, then observe for activity while operating relevant systems. Compare to expected signal_params.
Measure termination resistance between CAN_H and CAN_L across the network (~60 Ω). If open or far from expected, trace wiring for broken wires or missing terminator.
If bus is shorted to battery/ground, isolate segments by disconnecting connectors/modules one at a time to find the offending section.
Disconnect aftermarket accessories that tie into vehicle power or networks and re-check communication.
If wiring and supplies are good but BCM remains unresponsive, attempt communication via a known-good diagnostic interface; check for available software updates or reflash procedure from OEM.
If reprogramming is required and wiring/power checks pass but module still fails, replace BCM per manufacturer procedure and perform module pairing/initialization and relearn operations as required.

Likely causes

Loose/corroded BCM connector or poor ground at BCM
Open or shorted CAN high/low wiring near BCM or at common splice
Blown fuse or lost key-on power feed to BCM B
BCM B internal failure or corrupted software
Aftermarket alarm, radio or module incorrectly tied into network

Fault status

⚠️ Status

Stored when the vehicle communication bus does not receive/respond from Body Control Module B or when the module fails to respond to diagnostic requests. Indicates lost communication, not a specific component function failure.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

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