Check Engine Light Diagnostics

What does the CHECK ENGINE LIGHT usually mean?
There are hundreds of codes that could trigger your CHECK ENGINE LIGHT for dozens of reasons each. Even the most common reasons can have many possible causes. Some top CHECK ENGINE LIGHT codes are:

  • Problem with the Mass Air Flow (MAF) sensor or circuit. You may not notice any serious drivability problems, although there may be symptoms such as a general decrease in power or sluggishness. This could be caused by a simple connection problem of the sensor, a wiring connection may be bad or dirty or the Mass Air Flow sensor may be faulty.

  • System Running Too Lean. An oxygen sensor detected a lean condition (too much oxygen in the exhaust). You may notice a lack of power, detonation (spark knock), and/or a hesitation/surge on acceleration which could be caused by a dirty Mass Air Flow sensor or air filter, or a vacuum or exhaust leak in the system.

  • System Running Too Rich: The oxygen sensor detected a rich condition (or a too-high fuel to oxygen ratio). You may experience misfires with this condition. This condition can be caused by a dirty or faulty Mass Air Flow sensor, air filter, a blockage or restriction in the airstream, a fuel pressure, fuel injector, or fuel delivery problem.

  • Cylinder Misfire: A P0300 series of codes indicates a random or multiple misfire in your engine. You may find your engine harder to start, the engine may stumble, idle rough, and/or hesitate among other driveability symptoms. This could mean anything from faulty spark plugs or spark plug wires, a bad ignition coil, a vacuum or air leak, to a serious mechanic problem in your engine. This code is serious when flashing and can cause faulty catalytic converter(s).

  • Knock Sensor Circuit Malfunction: Your vehicle's computer constantly adjusts and retimes the engine so that it doesn't produce harmful pre-ignition detonation or knock. With this malfunction you may notice drivability problems including -not surprisingly-knocks and a lack of power and hesitation. It could mean the knock sensor is faulty and needs to be replaced, that there is a wiring short/fault in the knock sensor circuit, or that you have other problems that the knock sensor cannot control.

  • Insufficient EGR (Exhaust Gas Recirculation) Flow: Your vehicle recirculates exhaust back into the combustion chamber to better achieve optimal combustion chamber temperature and to reduce NOX (a harmful greenhouse gas). This light triggers when there is insufficient EGR flow in the combustion chamber and you may notice a pinging when the vehicle is at higher speeds. There may also be other symptoms. It could be a faulty sensor, valve or blockage in the EGR (tube) from a carbon buildup.

  • Catalyst System Efficiency below Threshold : The oxygen sensor after the catalytic converter is detecting that the converter is not working as efficiently as it should be (according to specs). You will likely not even notice any drivability problems though your vehicle may have anything from an oxygen sensor not reading (functioning) properly to a damaged exhaust manifold, or a bad catalytic converter.

And these are just a few of the hundreds of codes, causes, and symptoms. Each has multiple fixes.

Computer Diagnostic: As needed when the check engine light appears.

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What happens when I ignore the CHECK ENGINE LIGHT or put off service when my Southeast Auto Service technician tells me what's wrong?

There are two kinds of CHECK ENGINE LIGHT alerts. A non-flashing but lit CHECK ENGINE LIGHT, is usually a less severe problem that shouldn't cause immediate problems but needs to be checked as soon as possible, and a flashing and illuminated CHECK ENGINE LIGHT means your vehicle senses a critical system error (such as a major cylinder misfire ) and you need immediate attention before potentially breaking down and possibly damaging other critical and expensive parts. In this case, continuing to drive can lead to further damage rather quickly or can leave you stranded.

Driving the vehicle with a non-flashing generic code will almost certainly cause an increase in emissions and a decrease in fuel economy-which can be robbing you of up to 20% fuel efficiency at each fill-up. Looking at it a different way, based on $3 per gallon, typically you could be wasting $7.50 per fill-up or upwards of $300 per year.

As quite a few of the systems work interdependent of one another, an error in one system can affect the operation in another. EVAP codes (vacuum related), EGR, temperature, speed sensors, etc. can all have an effect on how the transmission acts and shifts, or how the engine performs, or the cooling fans turn on, etc. By ignoring issue these important warnings, this may be creating other critical issues.

Let us diagnose the reason your check engine light is on. Call (912) 876-4280