Check Engine Light Diagnostics
A warning light is a symptom, not a diagnosis. Check engine diagnostics reads the stored codes and tests the related components to identify the cause.
- AvailabilityCalls and messages 24/7
- WhereRoadside, yard or jobsite
- CategoryHeavy-Duty Truck Repair
- On-site repairWhere feasible and safe
About check engine light diagnostics.
A warning light is a symptom, not a diagnosis. Check engine diagnostics reads the stored codes and tests the related components to identify the cause.
A mobile mechanic can look at the unit where it stands, whether that is the roadside, a yard or a jobsite. That can avoid a tow and shorten downtime when the fault is suited to on-site work.
Part of Heavy-Duty Truck Repair.
When you might need it.
Any of these is a good reason to call and describe what the unit is doing.
Amber or red warning lights
Reduced power mode
Codes returning after being cleared
Poor fuel economy
What the service involves.
Scan-tool code reading
Inspecting the related sensors and wiring
Testing the suspected system
Explaining what the code means for your truck
Causes and good habits.
These are possibilities, not a diagnosis. The only way to know is to test the unit.
Possible causes
- Sensor faults and loose connectors
- Genuine system faults such as fuel or emissions
- Intermittent electrical issues
Practical tips
- A flashing or red lamp means stop safely
- Record the codes and when they appear
What to expect.
A code points to a system, not always to a single failed part. Further testing may be needed.
On-site repair depends on the fault, parts, vehicle condition, safety and service feasibility.
(437) 601-8551Before you call
- Exact location, and direction of travel on a highway
- Truck or trailer type, make and year if known
- What happened and what warnings you see
- Whether the unit is somewhere safe
- A number we can call back
From the first call to the fix.
Call or message
Tell us where the unit is.
Describe the fault
Symptoms, lights, noises, leaks.
Agree the plan
Feasibility and dispatch, discussed honestly.
Diagnose and repair
On site where it is possible and safe.
Services that often go together.
Engine Diagnostics & Troubleshooting
When a heavy-duty engine derates, stalls, loses power or throws fault codes, finding the actual cause matters more than clearing a light.
Sensor Replacement
Modern trucks rely on sensors to manage the engine, emissions and braking.
DPF / SCR System Diagnostics
Emissions systems cause many derates on modern diesels.
Electrical Troubleshooting
Electrical faults can be maddening.
Frequently asked questions.
Is it safe to keep driving with the light on?
A red or flashing warning means stop safely and call. For amber lights, get it checked soon.
How do I request this service?
Call (437) 601-8551 or message us on WhatsApp with your location and the issue. For non-urgent work, use the contact form.
Can every repair be done on site?
No. It depends on the fault, parts, vehicle condition, safety and feasibility.
Stranded on the Road? Let's Talk.
Tell us where your truck or trailer is located and what happened. Contact Fellows to discuss mobile repair options and next steps.
(437) 601-8551Have ready: exact location, truck or trailer type, what happened or what warnings you see, whether the unit is somewhere safe, and a callback number. Timing, dispatch and on-site repair depend on location, availability, the fault, parts and safety.