B3490

Code

Generic B — Body

Body Control Module Communication Fault

Brand: Generic

Type: B — Body

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Page language: EN

Causes

BCM has lost power or ground
Damaged or corroded connectors or wiring to the BCM
Open or short in CAN/LIN communication wires
Failed BCM or internal module fault
Bus termination fault or incorrect bus voltage levels
Another module pulling the network off-line or causing bus errors

Symptoms

Multiple body functions inoperative (lights, locks, wipers, etc.)
Instrument cluster warnings about communication
Intermittent or permanent loss of features controlled by BCM
Illuminated MIL or other dash fault indicators
Other modules reporting lost communication or network errors
Vehicle may enter limp mode for affected systems

What to check

Read all stored and pending DTCs from all modules; note freeze-frame and event counts
Verify battery voltage with key on and engine off (should be 11–14 V)
Inspect BCM connector for corrosion, bent pins, moisture or overheating
Check fuses and relays that feed BCM power/ignition circuits
Scan the CAN/LIN network for active nodes and network error counters
Perform wiggle test on BCM harness while monitoring communication

Signal parameters

CAN bus recessive voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both equal at recessive)
CAN bus dominant voltages: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (approximate values)
Typical CAN bus termination: ~60 ohms measured across CAN_H and CAN_L (two 120Ω in parallel)
BCM supply voltage (key on): ~11–14 V; sleep voltage near 12 V when vehicle off
LIN bus idle: pulled high to battery voltage; dominant state pulled low (~0 V)
Common CAN data rates: 250 kbps or 500 kbps (verify vehicle-specific rate)

Diagnostic algorithm

Retrieve DTCs from all modules and note time stamps, freeze frame, and if errors are present in other controllers.
Check battery state and connections. Charge or replace battery if voltage is low; ensure clean battery terminals.
Inspect BCM connector and wiring visually. Repair any corrosion, bent pins, damaged insulation, or poor pin engagement.
Verify BCM power and ground pins with a multimeter (key on): power circuit ~11–14 V, ground continuity near 0 Ω to chassis. Repair as needed.
With a scan tool, observe CAN/LIN bus for presence of the BCM node, bus error counters, and bus traffic. Confirm data from other nodes is present.
Measure CAN_H and CAN_L voltages at the BCM connector (recessive state) and check termination resistance across the two lines (~60 Ω).
If intermittent, perform wiggle tests and road test while monitoring communications to reproduce fault. Use an oscilloscope to look for noise, reflections, or missing frames.
Isolate the network if needed: disconnect non-essential nodes one at a time (or key off before disconnecting connectors) to find a node that causes bus failure.
Check for and apply any Technical Service Bulletins (TSBs) or software updates for the BCM or related network modules. Reprogram/configure replacement modules as required.
If wiring, power, grounds, termination and other modules check good and fault persists, consider BCM replacement as a last step. Follow manufacturer procedures for PIN security, programming and coding.
Safety note: de-energize circuits before performing connector repairs and follow vehicle-specific service manual procedures for airbag/vehicle security systems.