Ask The Experts

Recently a customer phoned the shop looking for help and advice…..

Our caller was distraught, to say the very least. A week ago his check engine light had come on. He phoned a local service center and they informed him that it was a serious issue and he should come in right away. He authorized a diagnostic service and $700.00 later, and several hours later he had a “supposed” fixed vehicle. After driving away the check engine light popped on again. He called the service center back and they told him he would need to return for further diagnostics and most likely something else was wrong. This conversation was not taken well by the customer and he decided to call around to get a second opinion. That is when he called us. I explained that although it could be likely the check engine light could come back on for another issue, the chances are slim. To further understand why the chances are slim, lets look at how the basics of the system works.

The check engine light (also know as a Service Engine Soon light or Malfunction Indicator Lamp) is strictly a way for the computer to notify the driver of a registered malfunction. Most vehicles today, the light looks like a little engine, some just say Service Engine, and some of the luxury and european vehicles have a display that contains a little more information. The actual name of the light is mis-leading. It should say something like “check vehicle” or “system malfunction”. The check engine light can come on for a multitude of reasons, not just issues with the engine. In the majority of times it has found an issue with the emissions control systems or electronics for the powertrain (engine, transmission etc.)

So lets look at how the system determines a fault has been found. The vehicles multiple computer systems monitor the vehicle thousands of times per second while the vehicle is in operation. When it detects an issue after two drive cycles it will turn on the light. A drive cycle is different from vehicle to vehicle, but essentially is about a certain amount of specific driving conditions and warm up and cool down periods. Unless there is a “hard” fault, meaning a serious issue that is a guaranteed recognized problem in the system (which will turn on the light right away and sometimes flash if it is really bad). The computer system waits for two drive cycles to make absolute certain there is an issue before it notifies you. The first step for the technician is to retrieve the fault code or error code. The code the computer gives is very generic and usually not helpful at all, but sometimes can help lead the diagnostic in the right direction. From there testing can be done and a determination can be made.

In a lot of cases, the check engine light will not keep the car from running and is usually not an emergency but should also not be ignored.

So let’s go back to our customers issue. The light came on right after he left the shop. It obviously had just started a drive cycle and was no where near completing two!! This would most likely indicate a “hard” fault. The computer knows with absolute certainty that there is an issue.

I explained this to our customer and he decided to bring it in to us due to the amount of hostility he received when he called the other service center back. Lo and behold, the part that the other service center installed was left disconnected! If they had driven the vehicle they would have realized this, also if they would have asked the customer to come in right away they could have resolved the issue quite easily. Everyone makes mistakes but in this situation poor customer service was the “hard” fault!

Check engine lights can be annoying when they are there staring you in the face but, the system is smart and is trying to save you from a breakdown or other serious issues.

Until next time, thanks for reading and keep those questions coming. We love hearing from you!!

Sincerely,

The Expert