Volvo Truck Light Control Module Problems-5 Reason & Fix It!

Volvo trucks are known for their durability and reliability. But even the best trucks can face issues over time.

Every time I climb into a Volvo truck, I know how much the little things matter. Lights turning on at the right time. Signals responding fast. Cabin dimmers behaving properly. All of this—what many drivers take for granted—is handled by one unsung hero: the Light Control Module, or LCM.

The LCM is the brain behind your truck’s lights. It controls everything from your headlights and brake lights to turn signals, trailer lighting, and dashboard illumination. When it works, you barely notice it. But when it doesn’t, things can get messy fast—especially at night or during bad weather.

I’ve seen trucks stuck on the side of the road just because a lighting failure went unchecked. Most of the time, it came down to a faulty LCM. And that’s why I’m writing this.

This guide is for truck owners, mechanics, and anyone who works with Volvo heavy-duty models. I’ll walk you through how the LCM works, what signs to watch out for, and how to spot a problem before it leaves you in the dark. My goal is to make this as clear and simple as possible, using real-world examples and easy terms. No fluff. Just solid help from someone who’s spent years under the hood.

Let’s get started by understanding how the LCM actually works.

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Common Problems with Volvo Truck Light Control Module

I’ve seen my fair share of electrical issues in Volvo trucks, and when lights start acting up, the Light Control Module (LCM) is often the hidden troublemaker. This little box is like the brain behind your truck’s lights. When it goes bad, the symptoms can look like a bunch of separate problems—but they’re all tied together. Let me walk you through some of the most common signs I’ve come across.

A. Flickering or Dim Lights

If your headlights or taillights keep flickering or seem dim, don’t brush it off. That’s not just annoying—it’s a sign something deeper is off. The LCM controls how much power goes to each light. So if the module starts glitching, your lights might not get a steady voltage.

Most times, flickering happens because of:

• Loose or corroded wiring
• Grounding problems
• A dying LCM that’s not regulating current correctly

One time, I had a Volvo VNL come into the shop with dim low beams. The bulbs were new. Wiring checked out. Turned out, the LCM was sending inconsistent signals. Swapping it out fixed the issue in minutes.

B. Failure of Specific Lights (Headlights, Taillights, etc.)

Ever had just your left headlight stop working? Or only one brake light fail while the others work fine? It might seem like a burnt bulb, but if replacing it doesn’t help, your LCM could be to blame.

The LCM sends separate commands to different lights—headlights, turn signals, taillights, marker lights—you name it. If a part of the module goes bad, it can stop sending power to one system while leaving the rest alone.

I’ve had to chase weird problems like taillights working only when the engine was off. After hours of testing, it turned out the LCM was sending signals at the wrong time. Replacing it solved the problem completely.

C. Dashboard Warning Lights

Your dash lights aren’t just for show. They’re warning you when something’s off. A bad LCM can trigger random warning lights that don’t match what’s actually going on.

For example, you might see:

• “Bulb Failure” messages when all bulbs are working
• “Check Electrical System” with no clear cause
• Lighting fault codes when scanned with a diagnostic tool

These alerts usually show up when the LCM misreads voltages or can’t communicate with other control modules. It’s like the module’s trying to talk, but it’s speaking the wrong language.

D. Inconsistent Light Behavior

This one drives techs crazy. One day your lights work fine. The next, they turn off by themselves or stay on after you shut the truck down. You might flip a switch and nothing happens—or it triggers the wrong lights.

This kind of behavior screams LCM trouble. I’ve seen cases where parking lights stayed on overnight and drained the battery. Or trucks where only one high beam worked, and the switch wouldn’t do a thing.

Sometimes the LCM gets stuck in a weird software loop. Other times, internal circuits are burned out. Either way, the light system becomes unpredictable and unsafe.

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Diagnosing Volvo Truck Light Control Module Problems

When a light on a Volvo truck stops working, I don’t jump to conclusions. I always start simple. A lot of electrical issues can look worse than they are. Over the years, I’ve learned that it saves time—and money—to follow a clear routine before touching the control module.

A. Preliminary Checks

1. Inspecting Bulbs, Fuses, and Wiring Connections

I begin by checking the most obvious things. A burnt-out bulb can easily be mistaken for a wiring issue. I pull the light housing and test the bulb. If it’s good, I move to the fuse box.

Each light on a Volvo truck is tied to a fuse. So I check for any blown fuses. I also make sure they sit tight in their sockets. A loose fuse can cause the light to flicker or not come on at all.

Next up is wiring. I inspect all the visible harnesses around the lights. I look for cracks, corrosion, or broken clips. Sometimes, road salt or moisture gets in and eats away at the wires. If I spot any green or white corrosion, that’s a red flag.

2. Ensuring There Are No Visible Signs of Damage

Before going deeper, I always take a step back and scan the area. Has the truck been in a recent collision? Are there signs of rodents chewing wires? Sometimes it’s something simple—a cut wire hanging near the wheel well or a cracked housing letting water in.

It sounds basic, but skipping these steps leads to guesswork. And guesswork in truck diagnostics wastes time fast.

B. Using Diagnostic Tools

1. Recommended Tools for Testing Volvo Truck Electrical Systems

Once I’m sure the basics are fine, I pull out my scan tool. For Volvo trucks, I use the Volvo Tech Tool (VTT). It talks directly to the truck’s ECU and gives detailed codes from the Light Control Module.

Another handy tool is a digital multimeter. I use it to test voltage at the light socket and to check continuity in wires. Sometimes I also hook up a Power Probe to inject voltage into a line to test the circuit.

Step-by-Step Process for Diagnosing LCM-Related Issues

Here’s the exact method I follow:

• Plug the scan tool into the OBD port under the dash.
• Turn the key to the “on” position but don’t start the engine.
• Run a full vehicle scan using VTT.
• Navigate to the LCM module in the list.
• Look for active and stored fault codes.
• Take note of the codes, then check the freeze frame data. It shows what was happening when the fault triggered.
• Use the wiring diagrams to trace the affected circuit.
• Confirm power and ground at the LCM connector using a multimeter.

This process helps me avoid replacing parts blindly. If power and ground are fine and the output from the module is dead, that’s a clear sign the LCM is at fault.

C. Identifying LCM Failure Indicators

1. Common Error Codes and Symptoms Pointing to LCM Failure

When the Light Control Module starts to go bad, the truck doesn’t always shout it. It whispers. Flickering lights. Rear lights going dark. Brake lights staying on. And sometimes the dash lights up with a warning.

I’ve seen codes like:

• MID 216 SID 254 FMI 12 – Internal failure in the LCM
• MID 216 SID 70 FMI 5 – Open circuit in the rear lamp circuit
• MID 216 SID 231 FMI 9 – Voltage out of range

These codes are solid clues. If I see multiple lighting circuits failing at the same time and the power supply checks out, the LCM jumps to the top of my suspect list.

2. How to Interpret Volvo Truck Diagnostic Codes

Volvo truck fault codes can look confusing at first. But once I break them down, they make sense.

• MID tells me which module sent the code. For lights, it’s usually MID 216 (LCM).
• SID stands for Subsystem Identifier. It points to the exact part being monitored—like a rear left light.
• FMI tells me the type of fault. FMI 5 usually means open circuit. FMI 12 means the module has given up.

By combining this info with what I see on the truck, I can pinpoint the root cause. No guesswork. Just logic.

IV. Solutions for Fixing Volvo Truck Light Control Module Problems

I’ve worked on plenty of Volvo trucks over the years, and when a light control module (LCM) starts acting up, it’s usually not subtle. Lights flicker. Indicators fail. And sometimes, the whole thing just goes dark. Fixing it doesn’t always mean a full replacement, though. Let me walk you through the different ways I’ve dealt with this issue—what’s worked, what hasn’t, and what you might try next.

A. Repairing the Light Control Module

Sometimes the LCM just needs a reset or a reprogram. I’ve had good luck fixing minor glitches without swapping out the whole unit. Here’s how I handle it.

Step-by-Step Repair or Reprogramming

1. Disconnect the battery
   I always start here. It prevents any short circuits and resets the system. Wait at least 10 minutes.
2. Remove the LCM
   It’s usually located under the dashboard or near the fuse panel. You’ll need a screwdriver or a socket set.
3. Inspect for damage
   Look for burnt pins, moisture, or cracked solder joints. If something looks off, that could be your culprit.
4. Use a scan tool
   I plug in a Volvo-compatible diagnostic scanner. It reads fault codes and lets me reprogram if needed.
5. Reprogram the module
   If the codes point to a software glitch, reprogramming may fix it. Make sure to update with the latest software version.
6. Reconnect and test
   After putting everything back, I test all lights. Headlights, brake lights, turn signals—the full set.

Repair or Replace?

If the module responds to reprogramming, that’s a win. But if I see burnt circuits or water damage, I skip the fix. It’s just not worth the risk of the lights failing again on the road.

B. Replacing the Light Control Module

Sometimes the module is too far gone. In that case, I go ahead and replace it. It’s not hard if you know your way around a few tools.

How to Replace the LCM

1. Disconnect the battery
   Safety first—always.
2. Remove the old LCM
   I locate the module and unplug all the connectors. Then, I unscrew it and pull it out gently.
3. Install the new LCM
   I line up the new one, plug everything back in, and screw it into place.
4. Program the new module
   This is a must. New LCMs often come blank. I use my diagnostic tool to sync it with the truck’s system.
5. Run a full test
   I always test all lights, run a diagnostic scan again, and check for any stored errors.

Tools and Components Needed

• Screwdriver set
• Volvo-compatible diagnostic scanner
• Replacement LCM
• Clean gloves and electrical contact cleaner (optional but helpful)

Cost Considerations

Here’s what I usually tell truck owners:

Buying a scanner may seem pricey, but it pays off if you work on trucks often. It saves you trips to the shop.

C. Preventive Measures to Avoid Future Issues

Fixing the LCM is one thing. Keeping it healthy is another. I try to do a few simple things to make sure I don’t have to fix it again anytime soon.

Regular Maintenance Tips

• Check wiring monthly
  Loose or frayed wires stress the module. I look under the dash and around the lights.
• Keep the truck dry
  Moisture kills electronics. I seal cracks around lights and inspect grommets.
• Clean the connectors
  Corroded pins cause signal drops. A quick spray with electrical contact cleaner works wonders.

Extending the LCM’s Lifespan

• Avoid overloading the lighting circuit
  Adding extra lights without relays puts strain on the LCM.
• Use OEM parts
  I’ve had issues with cheap aftermarket lights. They don’t always play nice with the module.
• Update software regularly
  Volvo pushes out updates to fix bugs. If you’ve got a scanner, check for them once in a while.

Volvo Truck Light Control Module Maintenance Tips

I’ve learned that regular care goes a long way with electrical parts—especially the Light Control Module (LCM). These modules control everything from headlights to trailer lights. If they go out, you’re not just losing visibility—you could lose time, safety, and money. Below are the steps I follow to keep LCM problems at bay.

A. Routine Inspections of Electrical and Lighting Components

Key Areas to Check Regularly

I always start with a visual check. It sounds basic, but it works. I look for:

• Cracked lenses or moisture inside light housings
• Flickering or non-functioning exterior lights
• Loose or frayed wires near the battery or fuse box
• Burn marks around connectors or plugs

If something seems off, I take a closer look. Even a small crack in a tail light can let in water. That moisture can trigger bigger issues inside the LCM.

How Frequent Checks Can Prevent Future LCM Problems

I make it a habit to check these parts every two weeks. It doesn’t take long—just five minutes before I hit the road. Spotting a weak light or damaged wire early has saved me from bigger problems down the line. It’s the difference between a quick fix and a tow bill.

B. Keeping the Truck’s Wiring and Connections in Optimal Condition

Tips for Ensuring Proper Wiring Integrity

I don’t mess around with damaged wires. If I see exposed copper or heat damage, I replace the whole section. A simple splice job can fail later under pressure or heat. I also wrap wires with high-grade electrical tape and keep them clear of hot engine parts or moving components.

I use wire loom tubing where possible—it’s cheap and shields against heat and rubbing.

Importance of Clean Connections to Avoid LCM Issues

Dirty connections can make a solid system act broken. I clean plugs and terminals with electrical contact cleaner and a soft brush. Then I use dielectric grease before reconnecting. It helps prevent corrosion and keeps moisture out.

Any sign of greenish corrosion around a plug or terminal is my cue to clean or replace it. Dirty connectors can confuse the LCM, causing random light failures or triggering warning messages on the dash.

C. Professional Maintenance Options

When to Seek Professional Help for LCM and Electrical Repairs

There are times I’ve hit a wall with diagnostics. If I get multiple warning codes or lights flicker even after I check the basics, I bring in a pro. Most Volvo dealers have diagnostic tools that can read the LCM directly. That gives you a clearer picture than guessing or swapping out parts blindly.

If the LCM itself needs reprogramming or replacing, it’s not something I try to do alone. That’s a job for someone with the right software and Volvo experience. It might cost more upfront, but it saves time and trouble later.

Frequently Asked Questions (FAQ)

Q1: What causes a Volvo truck’s light control module to fail?

From what I’ve seen, most LCM problems boil down to a few usual suspects.

• Wiring issues. Damaged wires, corroded connectors, or poor grounds can cut off the signal or power the LCM needs to work.
• Water intrusion. Moisture can sneak in through broken seals or damaged housings and short things out.
• Software glitches. A buggy software update or corrupted data can confuse the module.
• Wear and tear. Like any part that deals with constant input, the LCM can wear out with age.
• Voltage spikes. Jump-starts done wrong or battery surges can fry the circuit board.

One small fault can trigger weird light behavior across the truck. I’ve had trucks come in where just a single corroded pin caused all the rear lights to act up. It’s rarely random.

Q2: How can I tell if my Volvo truck’s LCM needs to be replaced?

There are a few clear red flags that scream LCM trouble.

• Lights flicker, stay on, or don’t come on at all.
• Warning messages pop up on the dashboard.
• Some lights work fine, while others act up—especially if it’s the same ones each time.
• Replacing the bulbs or fuses doesn’t fix the issue.
• Diagnostic scans point straight to LCM faults.

When one or more of these show up, I check the LCM early in the process. It saves a lot of time chasing symptoms.

Q3: Can I repair the LCM myself, or should I seek professional help?

It depends on your tools and comfort with electronics.

Some fixes are simple—like cleaning connectors, checking grounds, or reprogramming the unit. If you have a decent scanner and basic electrical knowledge, you might be able to handle those.

But if the circuit board is fried or the software is corrupt, that’s another story. Most people don’t have the gear to safely crack open an LCM or flash it with factory software. In that case, I always send it to a shop or replace it.

Q4: How much does it cost to replace a Light Control Module in a Volvo truck?

It’s not a cheap part, but the cost can vary a lot.

These prices depend on your truck model, where you live, and whether you buy new, used, or remanufactured. Some shops may bundle programming with installation, while others charge separate.

Q5: How often should I perform maintenance on the LCM?

There’s no set schedule, but I like to keep things clean and dry. Here’s what I usually check:

• Look for corrosion or loose pins during routine light checks.
• Scan for codes if warning lights flash or anything looks off.
• Make sure battery voltage stays steady—fluctuations can shorten module life.
• Inspect seals and housing after winter or heavy rain exposure.

The LCM doesn’t need regular service like an oil filter, but a little attention during inspections can stop big problems before they start.

Final Words

Light Control Module issues show up through flickering lights, error messages, or failed signals. I always begin with fuse checks, inspect all wiring, and check for signs of corrosion or moisture. Regular tasks like inspecting lights weekly and sealing loose wires go a long way in stopping problems before they start. Replacing or reprogramming the LCM solves most stubborn issues. Spot trouble early, and take action fast. A trusted Volvo technician can help if things get tricky. Drop your questions or share your own fix below. Let’s keep our Volvos shining bright and ready for every road ahead.