Semi-Truck Lighting or Body Control Module Fault – Headlights, Markers, or Turn Signals Not Working | UpFix

When Lights Stop Listening

You flip the headlight switch—and nothing. Maybe your headlights stay on after shutdown, or your marker lights flicker like there’s a short. The issue often isn’t the bulbs or wiring—it’s the Body Control Module (BCM) or Lighting Control Module (LCM) inside your truck.

These modules are the nerve center for lighting, wipers, and other accessories. They regulate voltage to multiple systems, monitor current draw, and communicate with the ECM. When they start failing, you’ll see chaos in your lighting circuits—and no amount of bulb changing fixes it.

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Common Symptoms

• Headlights or marker lights won’t turn on or off

• Turn signals blink rapidly or stay solid

• Running lights flicker while driving

• Fuse keeps blowing for no clear reason

• “Body Control Fault” message on dash

• Lighting relays click repeatedly even with key off

These problems commonly appear in Freightliner Cascadia, Kenworth T680, Peterbilt 579, Volvo VNL, and International ProStar trucks.

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Typical Fault Codes

While damaged wiring can cause lighting problems, recurring codes and flickering lights after wiring checks often point to internal BCM/LCM failure.

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Why BCMs and LCMs Fail

1. Heat from constant electrical load weakens transistors and regulators.

2. Moisture intrusion corrodes PCB traces and connectors.

3. Vibration and thermal cycling crack solder joints.

4. Voltage surges from alternators or jump-starts damage driver circuits.

5. High current draw from aftermarket lights overstresses output channels.

Once damaged, these modules can leak voltage to the wrong circuit or drop power to headlights entirely.

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Dealer Replacement vs. UpFix Repair

A new BCM or LCM can cost $1,000–$2,500 and may require VIN programming at a dealership. Used ones often mismatch configuration or carry the same underlying faults.

UpFix repairs your original module, keeping its programming intact—so it’s plug-and-play on return.

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How UpFix Repairs Lighting and Body Control Modules

1. Diagnostic test of each lighting output channel and relay driver.

2. Replacement of failed MOSFETs, regulators, and relay circuits.

3. Cleaning and re-sealing the board to prevent moisture damage.

4. Reflow of cracked solder joints from vibration.

5. Bench testing under simulated lighting load to confirm all outputs work within spec.

Every unit is validated on a power simulator that mimics headlight, marker, and turn signal loads, ensuring proper current draw and CAN communication before shipment.

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Real-World Example

A 2020 Kenworth T680 showed flickering headlights and repeated SPN 804 FMI 5 even after wiring repairs. The root cause was a failed low-side driver circuit in the BCM. UpFix replaced the driver chip, repaired corroded traces, and resealed the board. On reinstall, all lighting functions returned immediately—no programming or dealer visit required.

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Supported Brands and Modules

• Freightliner / Western Star – SAM Cab / SAM Chassis Modules

• Kenworth / Peterbilt – Smart Junction / LCM Units

• Volvo / Mack – LCM and VECU Integration

• International – BCM and Headlamp Power Modules

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Savings and Sustainability

Repairing instead of replacing means:

• Up to 80% cost savings versus new modules.

• 24–48-hour turnaround for most repairs.

• Zero reprogramming downtime.

• Lower environmental footprint: Each repaired BCM saves up to 2 lbs of copper and circuit waste from landfills.

By choosing repair, fleets reduce both electronic waste and the energy required to manufacture new parts.

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Get your truck back on the road and keep your costs low.
Send your part to UpFix for professional testing and repair.
We’ll restore it to like-new condition, save you up to 80 percent compared to buying new, and make it plug-and-play ready when returned.