When you’re hauling freight across the Delmarva Peninsula, your truck’s dashboard is your early warning system. While every warning light matters, three in particular tend to show up frequently. Taking action promptly will be necessary to protect your safety, your cargo, and your schedule.
At M&L Truck Service, we know that minutes matter when a warning light appears. That’s why we offer quick diagnostics and mobile truck repair within 60 driving miles of our shop in Federalsburg, Maryland. We frequently provide roadside service to truckers traveling through major routes like US-13, US-113, US-301, and Route 50.
NEW RESOURCE! Do you suspect that new dashboard warning light might be related to a fuse issue? Check out our list of warning light fuse box diagnostic tests you can use to rule out a fast roadside fix.
1. Check Engine Light (CEL)
Severity: High
Requires prompt attention, but may be safe to drive short distances depending on symptoms.
Why it’s critical:
Your CEL can indicate anything from a loose gas cap to serious engine trouble. On more modern semi-trucks, a lit CEL may also trigger derating (limiting your speed or power until the problem is fixed).
Immediate Action Protocol:
- If CEL is solid: Reduce strain on the engine, complete your route if it is safe to do so, and schedule a diagnostic ASAP.
- If CEL is flashing: Pull over safely and shut down the engine immediately. This could mean active engine misfire or severe fault that risks damage.
Diagnostic Questions You Can Ask Yourself on the Road:
- Did this light come on after fueling or maintenance?
- Is there any unusual noise, vibration, or smoke?
- Has your truck lost power or fuel efficiency?
Typical Diagnostic Costs at M&L:
- Basic engine code scan: $125
- Basic code reading: 1 Hour
- Full diagnostic: 1–2+ hours, depending on system and vehicle.
- Repairs: Heavily dependent on complexity of the issue, labor, and parts.
Prevention Tip: Keep up with manufacturer-recommended service intervals and use high-quality fuel to reduce injector and emissions system issues.
2. Brake Warning Light
Severity: Very High, Safety Critical
Why it’s critical:
Brake system failures can be catastrophic, especially in a fully loaded semi. This light could indicate low brake fluid, worn pads, parking brake engagement, or deeper hydraulic/air brake issues.
Immediate Action Protocol:
- If light comes on while driving, check that the parking brake is fully released.
- If brakes feel normal, continue with caution and schedule service as soon as possible.
- If you notice noise, vibration, pulling, or poor stopping power: pull over immediately and call for roadside assistance.
Diagnostic Questions:
- Do brakes feel soft, spongy, or slow to engage?
- Are there any metallic grinding sounds?
- Is the fluid level in the reservoir low?
Typical Diagnostic Costs at M&L:
- Basic inspection: $125
- Safety inspection: 1+ hour, depending on the number of axles.
- Minor brake service: Just replacing brake pads and rotors will take about 2 hours per axle for light-duty; 3-3.5 hours for medium and heavy-duty.
- Full brake job: If calipers, bearings, or seals need replacement or repair, the job can take several days depending on availability of parts.
Prevention Tip: Inspect brake fluid and pads at every PM service; keep air systems drained and dry to prevent corrosion.
3. Tire Pressure Warning Light
Severity: Medium to High
Can become urgent quickly.
Why it’s critical:
Underinflated tires reduce handling, increase blowout risk, and can destroy fuel economy. In a semi, that can mean lost time and costly roadside calls.
Immediate Action Protocol:
- Pull over at the next safe stop and check all tires with a gauge.
- Inflate to manufacturer-recommended PSI.
- If light remains on, you may have a sensor issue or a slow leak.
Local Service Tip: While M&L Truck Service does not perform tire repairs, we recommend Hitchens Tire in Milford, DE for tire replacement or repair. If the problem is sensor or system related, we can usually get you fixed up same-day.
Typical Diagnostic Costs at M&L:
- Tire Pressure Monitoring System (TPMS)/sensor diagnostic: $125
- Typical Service Time:1 Hour
- Sensor reset or replacement: Dependent on type of sensor and type of vehicle.
Other Important Lights to Watch
Every light on your dashboard has a purpose. While these three are the most commonly seen, lights for oil pressure, coolant temperature, ABS, and others are also important and deserve prompt attention. See the chart below for quick reference of what each symbol means. Feel free to give us a call any time during business hours to get an expert opinion on the severity of the issue.
Serving the Delmarva Peninsula
M&L Truck Service provides emergency roadside service during business hours and within 60 driving miles of Federalsburg, MD, including:
- Maryland: Salisbury, Cambridge, Denton, Easton, Princess Anne, Hurlock
- Delaware: Dover, Georgetown, Seaford, Delmar, Harrington, Smyrna
- Further Away: No roadside service, but always welcome in the shop.
Semi-Truck Warning Lights FAQ
A: It could be emissions system faults, fuel delivery issues, sensor malfunctions, or even a loose fuel cap. A quick code scan will pinpoint the cause.
A: Most scans can be completed in an hour or less; more complex scans may take 2 or more hours. Make sure you schedule an appointment so you can get in and out quickly.
A: Solid usually means a non-urgent fault that still needs attention soon; flashing often signals a condition that could cause damage or safety hazards if you keep driving.
A: Diagnosis costs no more than $125. Repair cost will depend heavily on what the issue is, parts needed, and labor time.
A: It all depends on what we’ve got going on in the shop. On a slow day for a simple repair, absolutely. If it’s a busy season and your repair is larger in scope, it will likely take a few days or longer.
When a warning light comes on, every mile matters
Don’t gamble with your route or your rig. Call M&L Truck Service now for expert diagnostics and fast, reliable repairs in Maryland and Delaware.
Meet Office Manager, Donna Darling
Donna is known for her excellent customer service skills, and is likely who you'll talk to when you book with M&L. Her first car was a Toyota, and her first job was babysitting.