All modern vehicles are equipped with an onboard computer diagnostic system (OBDII) that constantly monitors your vehicle’s major operating systems and most importantly the power-train (engine and transmission). The main purpose of monitoring these systems is to insure that the vehicle is operating at top efficiency with the lowest possible emissions. As fuel economy and emission control has become increasingly important and complex, your vehicle’s electronics systems need to constantly adjust and fine-tune various parameters according to driving conditions (such as vehicle load, temperature and air/fuel mix to name just a few). When the computer reads that any of these parameters do not fall within the acceptable range for operating the vehicle, your CHECK ENGINE LIGHT is lit to warn you that you may have a serious problem and to take your vehicle to a certified technician – such as your local AAMCO technician – to check the faults and restore it to manufacturer’s specifications.


What is the check?

Reading the codes from your car’s computer system is similar to a doctor measuring your blood pressure when you schedule a visit. High blood pressure doesn’t tell the doctor what is wrong with you it simply lets the doctor know there is something wrong and points him or her in the right direction to find out what it is. Just like the CHECK ENGINE LIGHT codes tell your AAMCO technician there is something wrong and points him or her in the right direction, too. If the code indicates a problem with your O2 (oxygen) sensor system, it doesn’t necessarily mean you need a new O2 sensor. Additional diagnostics pinpoints the exact cause of the “trouble” code so you don’t pay for parts or services you don’t need. Be wary of garages that read your code and tell you immediately that you need a major repair.

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.

These are just a few of the hundreds of codes, causes and symptoms, each has multiple fixes.


What happens when I ignore the CHECK ENGINE LIGHT?

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. Also, 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. Ignoring these important warnings may create other critical issues.

Finally, if you live in one of the areas that require it, you certainly cannot pass state mandated Emission/Smog inspection with your CHECK ENGINE LIGHT

Clean your engine easily

Try Carbon Cleaning !

Cleans your engine and eliminates carbon build up.
Preventive engine cleaning enables you to restore engine parts rather than replacing them, thereby saving vehicle owners on costly parts, such as a new turbocharger ($ 1.350 – 3.100), catalytic converter ($ 600 – 2.000), DPF ($ 600 – 2.000) or EGR valve ($ 370 – 500).

These problems result mainly from poor combustion, which stifles the engine.

So before replacing your engine parts, try Carbon Cleaning. A dirty engine as the result of carbon deposits is the new threat to vehicle performance.

Spark Plugs Heat Rating

The spark plug heat range has no relationship to the electrical energy transferred through the spark plug. The heat range of a spark plug is the range in which the plug works well thermally.  The heat rating of each spark plug is indicated by a number; lower numbers indicate a hotter type, higher numbers indicate a colder type.

Heat rating and heat flow path of Spark Plugs

Some basic structural factors affecting the heat range of a spark plug are:

  •     Surface area and/or length of the insulator nose
  •     Thermal conductivity of the insulator, center electrode, etc.
  •     Structure of the center electrode such as a copper core, etc.
  •     Relative position of the insulator tip to the end of the shell (projection)

The major structural difference affecting the heat rating is the length of the insulator nose.  A hot type spark plug has a longer insulator nose.  The insulator nose of a hotter spark plug has a longer distance between the firing tip of the insulator, and the point where insulator meets the metal shell.  Therefore, the path for the dissipation of heat from the insulator nose to the cylinder head is longer and the firing end stays hotter.  The insulator nose of a hotter spark plug also has a greater surface area that is exposed to more of the ignited gases and is easily heated to higher temperatures.  A colder spark plug functions in an opposite manner.

The heat range must be carefully selected for proper spark plug thermal performance.  If the heat range is not optimal, then serious trouble can be the result.  The optimal firing end temperature is approximately between 500°C (932°F) and 800°C (1472°F).  The two most common causes of spark plug problems are carbon fouling (< 840°F) and overheating (> 1470°F).

Causes of Carbon Fouling:

  •     Continuous low speed driving and/or short trips
  •     Spark plug heat range too cold
  •     Air-fuel mixture too rich
  •     Reduced compression and oil usage due to worn piston rings / cylinder walls
  •     Over-retarded ignition timing
  •     Ignition system deterioration

Pre-delivery fouling

Carbon fouling occurs when the spark plug firing end does not reach the self-cleaning temperature of approximately 450°C (842°F).  Carbon deposits will begin to burn off from the insulator nose when the self-cleaning temperature is reached.  When the heat range is too cold for the engine speed, the firing end temperature will stay below 842°F and carbon deposits will accumulate on the insulator nose.  This is called carbon fouling.  When enough carbon accumulates, the spark will travel the path of least resistance over the insulator nose to the metal shell instead of jumping across the gap.  This usually results in a misfire and further fouling.

If the selected spark plug heat range is too cold, the spark plug may begin to foul when the engine speed is low or when operating in cold conditions with rich air-fuel mixtures.  In some cases, the insulator nose can usually be cleaned by operating the engine at higher speeds in order to reach the self-cleaning temperature.  If the spark plug has completely fouled, and the engine will not operate correctly, the spark plug may need to be cleaned / replaced and the fouling cause identified.

Causes of Overheating:

  •     Spark plug heat range too hot
  •     Insufficient tightening torque and/or no gasket
  •     Over-advanced ignition timing
  •     Fuel octane rating too low (knock is present)
  •     Excessively lean air-fuel mixture
  •     Excessive combustion chamber deposits
  •     Continuous driving under excessively heavy load
  •     Insufficient engine cooling or lubrication

The most serious result of selecting a heat range that is too hot is overheating.  Overheating will cause the electrodes to wear quickly and can lead to pre-ignition.  Pre-ignition occurs when the air-fuel mixture is ignited by a hot object/area in the combustion chamber before the timed spark event occurs.  When the spark plug firing end (tip) temperature exceeds 800°C, pre-ignition originating from the overheated insulator ceramic can occur.  Pre-ignition will dramatically raise the cylinder temperature and pressure and can cause serious and expensive engine damage.  When inspecting a spark plug that has experienced overheating or pre-ignition, blistering on the ceramic insulator and/or melted electrodes can sometimes be found.

As a general guideline, among identical spark plug types, the difference in tip temperature from one heat range to the next is approximately 158°F to 212°F.