B2661

Code

Generic B — Body

Body Control Module Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 7 EN: 9 RU: 8

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Page language: EN

Causes

Open, shorted or corroded wiring or connectors to the BCM
Faulty BCM or internal transceiver failure
Loss of module power or ground (fuse, relay, battery connections)
Missing or incorrect CAN bus termination (resistors)
Bus off condition caused by another module flooding the network with errors
Incorrect or incomplete module programming or firmware mismatch after replacement

Symptoms

DTC B2661 stored in BCM and possibly other modules
Intermittent or complete loss of functions controlled by BCM (lights, locks, wipers, interior electronics)
Other modules reporting lost-communication DTCs (U-codes)
No response from BCM to a scan tool or inability to reprogram the BCM
Bus error or CAN bus off messages on diagnostic tool
Vehicle may show multiple unrelated system warnings or limp behaviour in affected systems

What to check

Verify battery state of charge and system voltage (12.4–14.8 V normal)
Read all stored DTCs from BCM and other modules; note freeze-frame and network-related codes
Inspect BCM power, ground, fuses and related relays for continuity and correct voltage
Visually inspect BCM connectors and wiring harness for corrosion, bent pins, damaged insulation and water ingress
Check for aftermarket devices (alarms, remote starters) that may be attached to the network and disconnect if present
Use a scan tool to view bus activity, node list and any modules reporting bus-off or high error counters

Signal parameters

Battery/ignition supply voltage at BCM (expected ~12–14.8 V)
CANH idle voltage ≈ 2.5 V (recessive) — typical range 2.0–3.0 V
CANL idle voltage ≈ 2.5 V (recessive) — typical range 2.0–3.0 V
Dominant bit voltages: CANH ≈ 3.5 ±0.5 V and CANL ≈ 1.5 ±0.5 V during dominant state
Differential voltage (CANH–CANL): ~0 V (recessive) and ~2.0 V (dominant)
Termination resistance CANH–CANL ≈ 60 Ω (vehicle dependent)

Diagnostic algorithm

Confirm B2661 present and note any accompanying codes from other modules
Verify battery voltage and charging system health; charge or replace battery if low
Check BCM power and ground circuits: inspect fuses/relays, measure voltages at BCM power pins with key on and key off as specified by service information
Perform a visual inspection of the BCM connector and harness for corrosion, water entry, damage or bent pins; repair as needed
With ignition ON, use a scan tool to list network nodes and check for modules that are offline or in bus-off state
Measure CANH and CANL voltages at the BCM connector with a DMM; compare to expected idle and dominant values. If values are out of range, inspect wiring for short to ground or battery
Measure termination resistance across CANH–CANL with ignition off; an open or very low value indicates missing/shorted terminators
If a short is suspected, isolate sections by disconnecting harness connectors or modules to locate the shorted segment (disconnect suspect module and re-check bus voltages/termination)
If a single module is transmitting errors or causing bus-off, disconnect or replace that module to confirm restoration of network communications
Check for recent module replacement or software updates; reflash or reprogram BCM per manufacturer procedure if communication is intermittent but wiring/power are good
If diagnosis points to BCM internal failure after harness and other modules are ruled out, replace BCM and program/configure per vehicle-specific procedures (do not install a new BCM without proper coding)
Clear DTCs and verify repairs by cycling ignition and driving vehicle while monitoring network for reappearance of B2661

Likely causes

Damaged CANH/CANL pair (short to ground or battery) near the BCM
Failed BCM transceiver or internal electronics
Blown BCM power/ignition fuse or weak battery connection to BCM
Faulty or missing CAN termination resistors (open/short)
Another control module stuck transmitting and causing bus-off or high error count

Fault status

⚠️ Status

BCM is not communicating properly on the vehicle network. The module reports a communication fault (timeouts, bus-off, or no response) and may be unable to send or receive messages.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-4 hours