B135A

Code

Generic B — Body

Body Control Module (BCM) Internal Fault

Brand: Generic

Type: B — Body

Views: UK: 2 EN: 3 RU: 7

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

BCM internal hardware failure (component or PCB fault)
Corrupted firmware or software bug
Intermittent or low supply voltage (battery/ignition feed)
Poor ground or high-resistance ground connection
Water intrusion or corrosion at BCM or connector
Physical connector/wiring damage or chafed harness

Symptoms

One or more body functions intermittent or inoperative (lights, locks, windows, wipers, etc.)
Instrument cluster or gateway reports BCM-related communication errors
Stored DTC(s) related to BCM or network communications
Module not responding to diagnostic scanner or intermittent responses
Exterior/interior lights or accessories operate erratically
Possible no-start if BCM controls immobilizer or starter enable

What to check

Scan for all stored and pending codes; record freeze-frame data and active network errors
Check battery voltage (resting and with ignition on) and charging system
Inspect BCM connector for corrosion, bent pins, water intrusion, or poor mating
Verify fuses and relays that feed the BCM
Measure supply and ground at BCM connector (backprobe) for proper voltages and continuity
Check CAN-bus lines for proper idle voltages and continuity to other modules

Signal parameters

Battery/rest voltage: ~12.4–12.8 V (engine off); >13.5 V when charging (engine running)
Minimum allowed voltage while cranking: typically >9.0–10.0 V (vehicle-specific)
BCM ignition/switched feed: approximately battery voltage with key on
Ground continuity: low resistance, ideally
CAN bus idle voltages: CANH ≈ 2.5 V, CANL ≈ 2.5 V (idle); dominant state CANH ≈ 3.5 V, CANL ≈ 1.5 V
Diagnostic tool should see BCM present on the network and report module voltage and fault codes

Diagnostic algorithm

Retrieve and document all DTCs and freeze-frame data from all networks with a capable scan tool.
Ask the customer about recent battery service, jump-starts, aftermarket installs, water intrusion, or intermittent symptoms.
Check battery state of charge and charging system; ensure stable supply voltage before further testing.
Visually inspect BCM and connector for damage, corrosion, moisture, or loose pins; repair or dry/clean as required.
Verify all related fuses and relays; replace any suspect items and retest.
Backprobe BCM power and ground pins: confirm proper voltage with ignition OFF/ON/cranking and check ground continuity to chassis.
Verify CAN-bus communication: check idle voltages and use a scan tool to confirm module presence; perform wiggle tests on harness while monitoring for errors.
If communications are lost to multiple modules, trace wiring harness and check for shorts/opens to ground or battery.
If supply, ground and communications are good, attempt a controlled soft reset: clear codes and power-cycle the BCM (follow manufacturer procedure).
Check for available software/firmware updates or reflash/reprogram the BCM per manufacturer instructions; some faults can be resolved by reprogramming.
If internal hardware fault persists after verifying wiring, power and software, consider BCM replacement. Follow vehicle-specific procedures for module programming, VIN/immobilizer pairing and theft deterrent reinitialization.
After repair or reprogramming, clear codes and verify all affected functions operate normally; road-test to confirm issue resolved.

Likely causes

Failed BCM electronics or corrupted internal memory
Blown fuse or damaged ignition/switched feed to BCM
Open or high-resistance ground at BCM
CAN-bus wiring fault causing communications errors
Water/corrosion at BCM connector pins
Recent battery replacement, jump start or software update left module in an error state

Fault status

⚠️ Status

BCM internal fault detected — module reported an internal error or is not communicating reliably. Further electrical and software diagnostics required.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-4.0 hours