It’s unwise to ignore light telling you to check engine
One of the top reasons a vehicle owner might search the web or head over to their regular service garage is when a dreaded check-engine light, or CEL appears. And it’s dreaded for good reason.
That simple little icon can mean everything from a loose gas cap to a failed engine, and most of us won’t know the reason until a tech scans the vehicle’s computer and completes a diagnostic inspection.
And to add to the confusion, in many cases there are no other symptoms, either before or after the repair. This often leads to the question “Did I really need that or was I just taken for a ride?”
Check-engine lights come on when a circuit, component or system fails a basic self-test that the on-board computer runs on every startup, or when it registers an out-of-spec reading when driving. When these controls and codes were first used in mainstream vehicles in the late 1980s, the check-engine light was strictly reserved for emissions-related items. But with the commonplace use of multiple computers on even the most basic entry-level vehicle, they can now be illuminated for other things, such as transmission faults.
The most common reason for a check-engine light is a loose gas cap, and some automakers are nice enough to display that message in plain English rather than a mysterious icon.
If this was your vehicle’s problem, you’ll have to wait a day or so after tightening the cap for the light to go out.
The system will have to run a test that requires at least one full startup and drive cycle (such as a commute to and from work) before it will turn the icon off.
Resist the urge to disconnect the engine’s battery to reset the system and turn the warning light off. If your vehicle’s radio has any type of anti-theft feature (and most do) you’ll be left with an inoperative audio system until you can get the security code entered. (You wrote that down in the owner’s manual, right?)
What do you risk in ignoring the light?
As there are literally dozens of reasons the light can come on in the first place, the risks are hard to determine simply by looking at the dash.
Leave a coolant temp sensor problem unfixed, for example, and your engine can over-fuel, and if too much unburned fuel gets into the exhaust system, it can ruin a catalytic converter.
Leaving an engine misfire unresolved can also ruin a converter, but if the misfire is caused by a lean-running condition you can damage cylinder head valves and more.
Almost all shops have a menu price for a basic scan, but sometimes a complete diagnosis can take time, especially when corroded or broken wiring is involved. Basic scan prices at the shop can range between $80 and $150.