B0450

Code

Generic B — Body

Body Control Module Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 16 EN: 32 RU: 25

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Page language: EN

Causes

Damaged or corroded wiring or connectors at the BCM or along the communication bus
Lost or intermittent power supply or ground to the BCM
Open, short or high-resistance condition on CAN/LIN bus (including shorts to battery or ground)
Missing or failed termination resistors on the CAN bus
Faulty BCM hardware or internal controller failure
Software/firmware mismatch, corrupted module memory or required reflash

Symptoms

One or more body functions inoperative or intermittent (locks, windows, interior lights, wipers)
Instrument cluster warnings or multiple module communication warnings
Unable to program or communicate with BCM using diagnostic tool
Random or persistent network errors or additional communication DTCs
Vehicle may enter limp or degraded mode for affected systems

What to check

Use a scan tool: read all stored and pending DTCs and freeze-frame data; note time of occurrence and ignition state
Verify battery voltage with engine off and cranking (should be >= 11.5 V cranking; resting ~12.4–12.8 V)
Inspect BCM connector for corrosion, bent pins, water ingress, or poor retention; check pin-to-pin continuity
Check fuses and fusible links feeding BCM power circuits
Measure BCM power and ground circuits for proper voltage and low resistance to chassis ground (
Backprobe CAN_H and CAN_L at BCM with ignition on; verify idle voltages and differential and check for shorts to B+ or ground

Signal parameters

CAN idle (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both near mid-supply)
CAN dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V during active bits)
Expected differential idle ≈ 0 V; active frames differential ≈ 2.0 V
Termination resistance: ≈ 60 Ω measured across CAN_H to CAN_L with ignition on (two 120 Ω in parallel)
BCM supply: nominal battery voltage with ignition on; typically 11–14.5 V under normal conditions
Ground circuit resistance: ideally < 0.5 Ω between BCM ground terminal and chassis

Diagnostic algorithm

Record all DTCs and freeze frame data with a scan tool. Attempt to communicate with BCM and note if the module appears on the network.
Verify battery state of charge and charging system health. Recharge or replace weak battery before further diagnosis.
Visually inspect BCM connector, seals and nearby wiring for damage, corrosion, water ingress, or rodent damage. Repair any physical defects.
Check fuses/fusible links for BCM power and accessory circuits; verify power at BCM pins with key on and engine running as required.
Measure and confirm good ground(s) from BCM to chassis/engine ground. Clean or repair ground connections if high resistance found.
Backprobe CAN_H and CAN_L at BCM: measure idle voltages and differential, then observe with an oscilloscope if available to confirm valid signals and frames.
Measure resistance across CAN_H and CAN_L with ignition on; verify ≈ 60 Ω. Check for short to battery or ground on each conductor.
If intermittent, perform wiggle tests and load tests on wiring while monitoring network for dropouts. Isolate sections of harness if needed.
Disconnect non-essential modules or aftermarket accessories from the bus and test to determine if an added device is causing errors.
If wiring, power and ground are within specifications and termination is correct, consult OEM service info for BCM reprogramming or known software updates. Reflash/update only when wiring verified good.
Replace BCM only after all network wiring, power/ground and termination are proven good. After replacement, program/configure per vehicle manufacturer procedures and clear DTCs, then road test to confirm repair.

Likely causes

Poor ground or low battery voltage to the BCM
Loose, corroded or damaged connector at the BCM
CAN bus short to supply or ground, or missing termination (most common communication causes)
Intermittent wiring harness fault (pin damage, chafing) near BCM or splice
Faulty BCM (less common after wiring and power/ground checks are performed)

Fault status

⚠️ Status

Body Control Module communication fault — intermittent or lost communication on vehicle data bus (CAN/LIN). Check power, ground, connectors, bus wiring and termination before replacing module.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-3.0 hours