Your Check Engine Light and What it Really Means

It is back on again! Should I have my car towed in? Is my engine bad?

These are just a few of the many things that we have heard over the years regarding that infamous and dreaded little light in your dash: the Check Engine Light (CEL).

But what does that little light actually mean? And unlike the Mayan prediction of the end of the world, your problem may be very minor – or it just may indicate a larger, more obscure problem.

On-Board Diagnostics System

Use of the CEL began with the introduction of the On-Board Diagnostics II system (OBD) starting in 1996. This system is a government mandated vehicle component that automatically checks and tests various vehicle emissions control items.

There is no magic to the way this system operates or what it is telling you; the light is only connected to components that control your vehicle emissions. That’s it! An illuminated light is simply telling you that your car has an item that may be malfunctioning or not performing correctly that ultimately may affect what is coming out of your tailpipe.

Now that we have the doom-and-gloom scenario out of your head (or maybe not…), what does that light mean to you? We recommend that you have the light source fault scanned to identify the code that will point to the root cause. Most of the codes relating to the fault are government mandated and generic, with the exception of some manufacturer specific codes. It may only mean that your car may not pass the state inspection. If your car is not due for a while, then you may be just fine as long as you know what it is on for. Generally any auto service center or auto parts store can see what is causing the light to come on – and it should only take a few minutes. The one advantage of going to a Porsche facility is that we can sometimes read more detail into the codes that may be more common in a Porsche use application.

So now you know what code is causing the light to come on. Now what? You can easily look up the code information to determine what it means. There are a few comprehensive sites online that give you a description of what the numerical code is, such as:

Common CEL faults

Here is a very short list of the most common CEL faults codes on Porsches that we typically see here at POWERTECH. These are fault codes only and not necessarily related to repairs:

  • 993 1996-1998:  Secondary Air Injection (SAI) very common and usually easily repairable, and oxygen sensors.
  • 996 1999-2004:  Cylinder misfires, oxygen sensors, mass air flow meter, and evaporative system.
  • Boxster 1998-2004:  SAI and same as 996 above.
  • 997/Boxster/Cayman 2005-Present:  Cylinder misfires
  • 996 Turbo 2001-2005: Cylinder misfires, mass air flow meter.
  • Cayenne 2004-present: Cylinder misfires, evaporative system.

What are some common issues seen on Porsches?

We have all read where you should tighten your gas cap to shut the light off, but in reality that is seldom the problem. Most often we see issues related to Secondary Air Injection (SAI), oxygen sensors, and cylinder misfires depending on the year of your Porsche. It can also be a lean/rich running condition caused by a mass air flow meter or stuck evaporative system valve. If it is a rich running condition, then that could cause excessive fuel consumption. A lean condition can cause a power loss or even possible engine damage.

Is the CEL flashing?

A flashing code is usually related to a cylinder not functioning correctly and should be considered potentially more serious than a steady light. Porsche’s recommendation for a flashing CEL is to not drive the vehicle as serious engine damage may result, such as cylinder or catalytic converter damage.

If the CEL is not flashing, and you have determined that the fault is not dangerous to the engine, and you are not due soon for state inspection, then the next step is your choice. In theory you should repair the issue as your tailpipe emissions may be altered from the manufacturers’ specification and may be polluting the atmosphere more than it should. But you do not necessarily have to do anything. Until the car needs inspection, having the CEL on will not prevent you from driving the car, however we do definitely recommend at least knowing why the light is on.

Problems incurred

One common problem, however, with Porsche owners attempting to diagnose and repair CEL faults on their own is that they often do not follow through on a complete diagnosis. For example; it is not uncommon for an owner to contact us and explain how they replaced all their oxygen sensors because of an oxygen sensor CEL light code – only to have the same codes come back again. In fact, the codes may have been only clues to another problem, such as a vacuum leak or intake air metering issue that were not corrected. Be careful with understanding what you are reading as this is a case where a little bit of knowledge can be an expensive thing; unnecessarily replaced components that may not be defective!

One final note on CEL faults: these codes are related in some way to an emissions related item. Federal law warranty on emissions components can be as long as 8 years/80,000 miles on items such as catalytic converters. Warranty time is directly related to your vehicle in service date so make sure you know what that date is!