B0173

Code

Generic B — Body

Body Control Module Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 8 EN: 10 RU: 13

AI status

Completed

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Page language: EN

Causes

Faulty or intermittent BCM (module hardware or internal software fault)
Damaged, corroded or loose connectors at the BCM
Open, short or high-resistance wiring on CAN or LIN bus (CANH/CANL, LIN, or discrete comm lines)
Missing or incorrect bus termination (faulty/missing 60 ohm termination resistors)
Low battery voltage or poor ground / chassis return affecting module operation
Blown fuse or power supply issue to the BCM

Symptoms

Multiple body electrical features inoperative or intermittent (lights, locks, windows, etc.)
Instrument cluster or other modules report communication errors
Malfunction indicator lights or message on dash about module communication
Intermittent operation of systems controlled by BCM
No response from BCM when commanded by scan tool

What to check

Read all stored and pending DTCs from all modules with a capable scan tool; record freeze frame and occurrence counts
Verify battery voltage (12.6 V nominal at rest) and perform a battery health test
Inspect BCM connector for corrosion, bent pins, pushed-out terminals or water intrusion
Check fuses and power feeds to BCM for correct voltage and continuity
Verify chassis and module ground points for tightness and low resistance
Measure CAN bus voltages with ignition ON (see signal parameters)

Signal parameters

CAN bus idle (recessive): CANH ≈ 2.5 V, CANL ≈ 2.5 V (both half-supply)
CAN bus dominant: CANH ≈ 3.5 V, CANL ≈ 1.5 V, differential ≈ 2.0 V
Typical CAN data rates: 125 kbps, 250 kbps, 500 kbps or 1 Mbps (verify vehicle-specific rate)
LIN idle: resting voltage near battery/regulated reference (vehicle-specific), single-wire low speed
Termination resistance: approx. 60 ohms measured across CANH to CANL with ignition ON
Message timing: periodic BCM messages often every 10–200 ms depending on signal (verify with scope/scan tool)

Diagnostic algorithm

Connect a full-function scan tool, read all modules and record codes and module presence. Note if BCM is reported as present.
Check battery voltage and inspect main power and ground to the BCM. Repair any low-voltage or poor-ground issues.
Inspect BCM connector and harness for physical damage, corrosion or moisture. Repair terminals or harness as required.
Verify fuses and relays that supply BCM power. Replace blown fuses and retest.
With ignition ON, measure CANH and CANL at the BCM connector: verify idle and dominant levels and measure termination resistance.
If voltages or termination are out of range, trace wiring for short to battery/ground or opens. Repair wiring, solder joints or terminals as needed.
If electrical checks are good but communication is intermittent, use a lab scope or CAN bus analyzer to capture frames and look for noise, bus errors or a module flooding the network.
Isolate sections of the network if possible (disconnect suspected modules one at a time) to find the device causing the fault.
If wiring and network look good and BCM still does not communicate, check for required software updates or reprogramming history and perform programming/reflash as specified by manufacturer.
Replace BCM only after confirming wiring, power, grounds and bus integrity. After replacement, program and configure the new module and verify all systems.

Likely causes

Poor power/ground connections at BCM
Damaged connector pins/corrosion at BCM or splice point
Open or shorted CANH/CANL wiring near BCM
Missing termination resistor or short to battery/ground on bus

Fault status

⚠️ Status

Body Control Module communication fault detected — messages to/from BCM are missing, corrupted or intermittent. Check power, grounds, connectors, and vehicle network wiring.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-4 hours