Tech Tip of the Week | Encks Auto Repair By Paul Enck | Call: 727-822-1
That little yellow or red engine icon on your dashboard is one of the most misunderstood warning signs in any vehicle. Some drivers panic. Most ignore it and hope it goes away on its own. According to Paul Enck from Encks Auto Repair, neither response is the right one. The check engine light comes on for a reason — and understanding what it means can be the difference between a small repair bill and a very large one.
The short answer is yes — always.
“When the check engine light comes on, you see that little engine, that little yellow or red mark on your dash — should we be concerned? Absolutely. That light comes on for a reason.”
— Paul Enck, Encks Auto Repair
The check engine light does not discriminate between minor issues and major ones. It simply tells you that your vehicle’s onboard computer has detected something outside of its normal operating parameters. The only way to know how serious it is — is to have it properly diagnosed.
Not every check engine light signals an expensive repair. One of the most common triggers is something as simple as a loose gas cap.
If your gas cap is not fully tightened after refueling, the fuel system loses pressure and the vehicle’s computer registers it as a fault. Tightening or replacing the gas cap can clear the light in some cases. It is always worth checking this first before assuming the worst.
Pro Tip: After refueling, always turn your gas cap until it clicks. It is a ten-second habit that can save you an unnecessary trip to the shop.
Here is where the check engine light becomes a financial conversation. Paul walks through a real-world example that illustrates exactly why ignoring the light is never a good strategy.
“This car tells us with this instrument — we’ve gone through and run all the tests — that it has a catalytic efficiency problem, which could be the catalytic converters. There you’re looking at a couple thousand dollars. But in this case it turns out to be oxygen sensors, which are three or four hundred dollars.”
— Paul Enck, during live vehicle diagnosis
The oxygen sensors in this vehicle were the root cause of the problem. Left unaddressed, those failing sensors would have continued to damage the catalytic converter — turning a three to four hundred dollar repair into a two thousand dollar or more replacement.
“If you don’t replace those, then you will be replacing the catalytic converters. So the cost of the maintenance repair and fixing the problem overrides not doing anything about it and hoping the light will go out and go away.”
— Paul Enck, Encks Auto Repair
When your check engine light comes on, a technician connects a diagnostic scanner to your vehicle’s OBD-II port — a standardized connector found in all vehicles made after 1996. The scanner reads fault codes stored by the vehicle’s computer, which point to the system or component that triggered the light.
Here is what the diagnostic process typically looks like:
Step 1 — Connect the scanner
The technician plugs a diagnostic tool into the OBD-II port, usually located under the dashboard near the steering column.
Step 2 — Read the fault codes
The scanner pulls stored and pending codes from the vehicle’s computer. Each code corresponds to a specific system or component that has fallen outside acceptable parameters.
Step 3 — Interpret the codes
Fault codes point technicians in the right direction but do not always identify the exact failed part. A skilled technician uses the codes as a starting point and performs additional tests to pinpoint the true cause.
Step 4 — Confirm the diagnosis
Further testing — such as live data readings, component tests, or visual inspection — confirms which part is actually at fault before any repair is recommended.
Step 5 — Repair and clear
Once the repair is completed, the fault codes are cleared and the vehicle is tested to confirm the light does not return.
The check engine light rarely fixes itself. In most cases, the underlying problem continues to worsen the longer it goes unaddressed — and in many cases, one failing component puts additional strain on related parts.
The pattern Paul describes is extremely common:
Ignoring a warning light does not make the problem go away. It almost always makes the eventual repair more expensive.
Not all check engine lights carry the same urgency. Here is how to read the situation:
Steady light — schedule a diagnosis soon
A steady check engine light means the fault has been detected but is not currently critical. You can typically drive the vehicle but should have it diagnosed within a few days.
Flashing or blinking light — stop driving as soon as it is safe
A flashing check engine light indicates an active misfire that can cause rapid and serious damage to the catalytic converter. Pull over when safe and have the vehicle towed or inspected immediately.
Check engine light combined with other warning lights — treat it as urgent
If the check engine light appears alongside temperature warnings, oil pressure warnings, or other indicators, treat it as an emergency and do not continue driving.
What you can check yourself:
When to go straight to a shop:
1. Is it safe to drive with the check engine light on?
It depends on how the vehicle is behaving. If the light is steady and the car drives normally, you can typically drive it for a short period but should have it diagnosed promptly. If the light is flashing or the vehicle is running poorly, stop driving and have it inspected immediately.
2. Can a loose gas cap trigger the check engine light?
Yes. A loose or faulty gas cap is one of the most common and least serious causes of a check engine light. The fuel system is designed to be sealed, and any pressure loss — including from a loose cap — can trigger a fault. Always check your gas cap first.
3. Will the check engine light go away on its own?
Sometimes, if the issue was temporary — such as a momentary sensor glitch or a loose gas cap that has since been tightened. However, in most cases the light will remain on until the underlying problem is repaired and the codes are cleared by a diagnostic tool.
4. What is the difference between a steady and a flashing check engine light?
A steady light indicates a fault that has been detected but is not immediately critical. A flashing light signals an active engine misfire, which can cause rapid damage to the catalytic converter and other components. A flashing light should be treated as urgent.
5. How much does a check engine light diagnosis cost?
Diagnostic fees vary by shop but typically range from fifty to one hundred fifty dollars. Many shops will apply the diagnostic fee toward the cost of the repair if you proceed with the work. It is a worthwhile investment compared to guessing at parts.
6. Can I use a cheap OBD-II scanner from the auto parts store to diagnose it myself?
Basic scanners can read fault codes, which gives you a starting point. However, fault codes identify a system or circuit with a problem — not necessarily the exact failed component. Misinterpreting a code and replacing the wrong part is a common and costly mistake. Professional diagnosis goes beyond just reading codes.
7. What are oxygen sensors and why do they matter?
Oxygen sensors monitor the amount of oxygen in the exhaust stream and send that data to the engine’s computer, which uses it to regulate the fuel-to-air mixture. When they fail, the engine runs inefficiently and the catalytic converter is forced to work harder, eventually leading to premature failure.
8. How much do oxygen sensor replacements typically cost?
Oxygen sensor replacement generally ranges from one hundred fifty to four hundred dollars depending on the vehicle, how many sensors need replacing, and labor rates in your area. Compared to catalytic converter replacement, which can run from one thousand to two thousand dollars or more, addressing oxygen sensors early is a significant cost saving.
9. What is a catalytic converter and why is it so expensive to replace?
The catalytic converter is an emissions control device that converts harmful exhaust gases into less harmful substances before they exit through the tailpipe. It contains precious metals — including platinum, palladium, and rhodium — which make it expensive to manufacture and replace.
10. Can a bad oxygen sensor really cause catalytic converter failure?
Yes. When oxygen sensors fail, the engine may run rich — meaning too much fuel enters the combustion chamber. Unburned fuel then enters the exhaust system and can overheat and damage the catalytic converter over time. This is exactly the chain of events Paul describes in this Tech Tip.
11. How many oxygen sensors does my vehicle have?
Most vehicles have between two and four oxygen sensors depending on the engine configuration. Vehicles with a V6 or V8 engine typically have four — two upstream sensors before the catalytic converters and two downstream sensors after them. A diagnostic scan will identify which specific sensor has triggered the fault.
12. What other common issues trigger the check engine light?
Beyond gas caps and oxygen sensors, common causes include a faulty mass airflow sensor, failing spark plugs or ignition coils, a malfunctioning EGR valve, evaporative emission system leaks, a failing thermostat, or issues with the transmission. Each requires proper diagnosis to identify accurately.
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