Almost daily we receive inquiries about Check Engine Light Diagnosis. There are a lot of consumers that believe we can just hook a tool to your vehicle and it will tell us what is wrong with the car. A lot of times, the consumer has already retrieved the code and they would like to know what is wrong with their vehicle and what it is going to cost to fix it. We are going to address this issue in the next couple articles.

Check Engine (Service Engine Soon) Light

When the computer (aka – ECM, PCM, or ECU) of your vehicle recognizes a system, circuit or sensor that is working out of parameters, it will signal your Check Engine Soon/Service Engine Soon light to come on. Vehicles that were produced from 1996 on have OBDII or On Board Diagnostics of the Second Generation. This system has a computer that will store a trouble code to indicate the system, circuit or condition that the computer sees has the issue. It may also store freeze frame data about the condition as to how long the engine had been running, the throttle position at the time, the speed being traveled at the time, engine operating temperature, and ambient air temperature. Vehicles produced prior to 1996 have computers that were equipped with On Board Diagnostics that were not as sophisticated, so the information is much less specific.

Trouble Codes

When you scan a vehicle and retrieve the trouble codes, there are a variety of different trouble codes you can encounter. Those that start with a P0 are Powertrain Codes, U0 are Communication Codes, C0 are Chassis Codes and B0 are Body Codes. In this article I will refer to P0 – Powertrain codes on a 1996 or newer vehicle.

I will give you an example of some of the trouble codes that can be stored in your computer:

  • P0300 Random engine misfire detected
  • P0420 Catalyst System Low Efficiency
  • P0401 Exhaust Gas Recirculation Flow Insufficient
  • P0171 Fuel Trim System Lean
  • P0174 Fuel Trim System Rich

None of these trouble codes are telling us what is wrong with the vehicle, just the condition that it sees. Pinpoint testing needs to be performed to find what is causing the computer to see this trouble code. For instance, on the PO401 Exhaust Gas Recirculation Flow Insufficient condition, a lot of people will assume you have an EGR Valve that needs to be replaced. But there are other components in that system like the EGR Solenoid and DPFE Sensor, just to name a couple, that can fail and sometimes blocked passages in the EGR System can cause that condition.

Why You Need An Experienced Technician

It takes time, proper diagnostic equipment, and a very educated and experienced technician to diagnose a Check Engine Light/Service Engine Soon Light. We will go into a little more detail on that topic in our next article.

All About Automotive Offers The Best Quality Auto Repair & Auto Maintenance in Gresham

Steve and Karen Johnston are owners of All About Automotive, providing auto repair and auto maintenance in Historic Downtown Gresham. If you have questions or comments, call them at 503-465-2926 or email them at [email protected].

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