Check Engine Light Testing and Repair
Check engine lights can drive you nuts. The check engine light comes on, you open the hood and sure enough the engine is right there where it belongs. First the light comes on, then it goes off and just when you think it is okay, the light comes back on again.
The check engine light, or Malfunction Indicator Lamp (MIL) on today’s vehicle can check for over 1500 problems and conditions. The computer control system is extremely complex and the MIL is letting you know the vehicle has a problem with the engine fuel and ignition management systems.
When the light comes on a Diagnostic Trouble Code (DTC) is stored in the computer memory. This code can tell us which of the several systems the engine computer saw the problem with. Contrary to what most people believe it does not tell what is wrong with the vehicle.
The trouble code is only the start of the testing process. While the trouble code and freeze frame data help in finding the problem they still may not give you the answer. For example, an oxygen sensor code could set. This code could state the sensor is not responding as the computer
expects it to. This does not mean the sensor is faulty. There are several reasons for this problem to happen. There could be a cracked hose causing a vacuum leak, loose connection, leaking fuel injector or several other things. Any of these problems will cause a change in the fuel mixture which the computer attempts to correct. When the computer reaches the limit of the correction range a code will set and the check engine light will illuminate.
Off to the auto parts store the car owner goes to get the code read. The little code reader shows an oxygen sensor code, the parts house sells an oxygen sensor, the DIY car owner installs it and a couple days later the light is back on with the same code, “stupid cars and their stupid computers” thinks the unhappy car owner.
In this case the code set will usually be one of the oxygen sensor codes.
This code sets because the computer makes a change to the fuel mixture and the oxygen sensor does not respond. The computer sees the lack of response and determines the oxygen sensor is faulty. The computer’s test results are only accurate when the
rest of the system is operating as it was designed. A broke vacuum hose which allows extra oxygen into the engine is not normal. The computer has no way of knowing the hose is broken so the computer’s test results do not show the actual problem.
In this example the vehicle owner changed the part the code indicated and parts store recommended it as well but it did not solve the problem. A trip to Diedrick’s and the broken hose would have been found and repaired for much less than the cost of replacing the oxygen sensor.
This is where it is important to have the proper equipment to find the problems quickly and efficiently. We have most of the original equipment manufacture (OEM) level scan tools for the vehicles we work on. Factory scan tools help find problems quickly, saving you money. We also subscribe to OEM level information to allow us to determine the trouble quickly and accurately as well as having lab scopes that give us a precise look as the signals coming from the sensor to the computers.
If your check engine light comes on, call Diedrick’s to have your problem solved quickly and correctly the first time.