B3773

Code

Generic B — Body

Body Control Module: Serial Data Line Short to Ground

Brand: Generic

Type: B — Body

Views: UK: 14 EN: 12 RU: 12

AI status

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Page language: EN

Causes

Damaged wiring harness where the serial data wire contacts chassis ground
Shorted connector, broken insulation or pin contacting ground
Faulty or water-damaged sensor/module on the same network pulling the line to ground
Corroded or loose ground or connector at BCM or network node
Internal BCM hardware failure (less common)

Symptoms

Multiple body or convenience systems inoperative or reporting faults (locks, lights, HVAC, etc.)
Intermittent or permanent loss of communication with BCM or other modules
Related modules store communication DTCs
Possible blown fuse for network power or loss of certain features

What to check

Scan all modules and record all stored and pending codes and freeze frame data
Perform a visual inspection of wiring, connectors, and grounds related to the BCM and nearby harnesses
Check for recent service or aftermarket installations that tapped into data lines
Check related fuses and power/ground circuits for the BCM
Backprobe the serial data line at the BCM connector to measure voltage and continuity

Signal parameters

LIN (single-wire) — idle pulled high through resistor (approx. battery voltage via pull-up); dominant/active ≈ 0 V
CAN (two-wire differential) — recessive ~2.5 V on both CAN_H and CAN_L; short-to-ground will pull one or both lines toward 0 V and collapse differential
Expected resistances: with power off, data line to ground should read high resistance (kΩs); a short to ground will read near 0 Ω
Quiescent current on a shorted line may be higher than normal; use a scope to view communication waveforms

Diagnostic algorithm

Retrieve all codes and note which modules report communication errors; clear codes and see if B3773 returns.
Visually inspect BCM connectors, harness routing and body panels for chafing, corrosion, or water entry. Pay attention to areas near hinges, doors, and engine bay pass-throughs.
Check relevant fuses and battery/ground connections for BCM. Repair any poor power/ground first.
With ignition ON (engine off), backprobe the suspected serial data line at the BCM connector and measure voltage. Compare to expected idle level for the system (see Signal Params).
If the line is at or near 0 V, remove connectors to peripheral modules one at a time (or isolate branches) to locate which branch pulls the line to ground. After disconnecting a branch, re-check the line voltage.
If connectors are disconnected and the line remains shorted, perform continuity test (engine off, battery disconnected) between the data line and chassis ground. Low resistance indicates a direct short; trace wiring to find damage.
Use a lab scope to view the waveform while modules are connected to confirm whether the bus is shorted or only intermittently disturbed.
Inspect and test suspected modules by disconnecting them and re-checking the bus. Replace or repair the module only after isolating it as the cause.
Repair damaged wiring or connectors (splice replacement, protective sleeving, secure routing). Restore any corroded terminals and ensure proper sealing.
After repairs, clear codes and verify normal communication across modules. Re-check for intermittent faults by wiggling harness and operating affected systems.
Safety note: when diagnosing shorts, work with battery disconnected for continuity checks and use fused test leads when injecting power to avoid further damage.