B1D2A

Code

Generic B — Body

Body Control Module: CAN Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 4 EN: 6 RU: 1

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Page language: EN

Causes

Open or short in CAN wiring (CAN-H or CAN-L)
Poor or missing ground or power to the BCM
Faulty BCM or other module pulling the bus to dominant state
Missing or failed bus termination resistor(s)
Connector corrosion, bent pins, or damaged harness
Incorrect module programming or firmware mismatch

Symptoms

Intermittent or complete loss of body-related functions (locks, lights, windows)
Multiple modules show communication errors or fail to respond to scan tool
Instrument cluster or message center errors/warnings
Erratic module behavior or features working intermittently
Possible vehicle fail-safe modes or limp features engaged

What to check

Use a diagnostic scanner to confirm B1D2A and read related U/B codes from other modules
Visually inspect BCM connector(s) and CAN harness for corrosion, damage, or loose pins
Verify BCM supply voltage and ground(s) with key on (battery voltage present and good ground)
With ignition off, measure resistance between CAN-H and CAN-L at two points on the network (expected ~60 Ω if two 120 Ω terminators present)
Measure CAN-H and CAN-L voltages with ignition on and no communication (recessive state): each line ≈2.3–2.7 V; verify differential and absence of stuck-dominant levels
Check for shorts to battery or ground on CAN-H/CAN-L with no power applied

Signal parameters

CAN bus nominal idle voltages: CAN-H ≈2.3–2.7 V, CAN-L ≈2.3–2.7 V (recessive)
Dominant state differential typically ~1.5–3.5 V depending on network
Expected bus termination equivalent resistance ≈60 Ω across CAN-H and CAN-L (two 120 Ω terminators in parallel)
Common CAN baud rates: 500 kbps, 250 kbps, 125 kbps (confirm vehicle-specific rate)
Use oscilloscope to verify clean differential CAN waveform, correct bit timing, and absence of extended dominant periods

Diagnostic algorithm

Confirm code and record freeze frame and occurrence data with a scan tool.
Check battery voltage and key on power to BCM; verify good battery supply and primary fuses.
Perform a visual inspection of BCM connectors and nearby wiring for damage, corrosion, or rodent chew.
With ignition off and battery disconnected if required by service procedures, measure resistance between CAN-H and CAN-L at multiple locations; expect ≈60 Ω. If open or high, inspect for missing terminators or open harness.
With ignition on, use a DMM to check CAN-H and CAN-L idle voltages at the BCM connector and at points along the bus. Look for stuck-high/low or asymmetry.
Use an automotive oscilloscope or CAN diagnostic tool to view waveform quality and identify where dominant states or noise appear. Compare waveforms at BCM and at other modules to localize fault.
Disconnect non-OEM or suspect accessories and repeat checks to rule out aftermarket interference.
If wiring and termination check good, verify other modules on the same CAN segment for communication and DTCs. If one module is pulling the bus low, isolate by disconnecting modules one at a time while monitoring the bus.
Inspect and repair damaged wiring, terminals or grounds. Replace faulty termination resistor(s) if needed.
If wiring and external modules are verified good, consider BCM reflashing or replacement per manufacturer procedure. If replacing BCM, ensure correct programming and module coding.
After repairs, clear codes and perform full re-check of communication, and monitor for reoccurrence.

Likely causes

Damaged CAN wiring between BCM and main CAN backbone
Loose/poor ground at BCM or chassis ground point
Failed/missing 120 Ω termination resistor(s) (net resistance ≈60 Ω expected across CAN-H/CAN-L)
BCM internal failure (hardware or firmware)
Short to battery or ground from an aftermarket accessory on the CAN lines