OBD Diagnostics Tips

The check engine light is no reason to get upset and let your cheese slide off your cracker. It simply means that a small problem is presenting itself in the engine and powertrain management system, which is strictly electrical. It has nothing to do with the mechanical aspect of your vehicle.

Today's vehicles have evolved to the point that a computer operates all aspects of the engine and in many cases the transmission as well. In the past, all operation was manual and quite inefficient from a fuel efficiency and power standpoint. The carburetor had a fixed setting for fuel mixture, which had no way of adapting to different air temperatures and altitudes, which is related to air density. The carburetor also had accelerator pumps, which pour fuel into the engine every time you accelerate, to compensate for vacuum deficiencies.

Now your vehicle has a computer that has the ability to sense changes in the environment, such as load, demand from operator, engine temperature and how efficiently the engine is burning fuel. When it comes to efficiency, it senses the amount of unburned oxygen and fuel in the exhaust via the oxygen sensors and adjusts the fuel trim so the engine burns as much of the fuel as possible with as little waste as possible.

To accomplish this feat, the computer has sensors that inform it of all the current conditions that it uses to make determinations as to the plan of attack to optimize the current demands. The computer makes many decisions every second and operates actuators and other devices to control the operation of the engine. Lastly, it has the oxygen sensors to inform it on how effective its operation is at the present. It will control the amount of fuel going into the engine according to these sensors.

If the computer receives an irregular signal from any of its sensors or actuators indicating a problem, it will immediately store the failure in its memory and respond with a code to correspond with the problem. The computer, in response to setting a code, will illuminate the check engine light saying, "Yo, I have a problem," to the operator. All you need to do is hook up an inexpensive code scanner to the OBD (on board diagnostics) port under the driver's side of the dash just to the left of the steering wheel on most cars. It will display the problem in a code that can be cross-referenced with the code sheet for an explanation of exactly what is wrong. You can purchase the code scanner at most automotive parts stores.

Locate the OBD outlet under the dash, generally on the driver's side below the steering column. Insert the cable end of the code reader into the OBD terminal outlet. Turn the ignition key to the "On" position with the engine off. Press the button on the code scanner, which is for reading the codes. It will take a moment or two and the scanner will display a four-digit code in the form of a number, for example 1460. If there is more than one code, press the "Next" button. Write all the codes down.

Use the code interpretation sheet provided with the scanner to cross reference the numbered codes to the explanation for these codes. Check any of the code related items prior to condemning and replacing them. The computer saw a discrepancy in the operation or signal of the item that caused the service engine soon light to come on. Always check the wiring connector and the condition of the component first. In most cases, if there is power to, or no signal from a component, it is likely in need of replacement.

There is one circumstance that requires much more diagnostics. If the code for an oxygen sensor comes on, it means that the computer saw a discrepancy in the fuel mixture. This does not necessarily mean that the sensor is bad. Anything from a bad plug wire, spark plug, mixture, vacuum leak and many other things can produce the same effect. Unless the code says, for example, B1 S1 heater inoperative, (which is a true fault), the sensor is probably good.

After the repair is completed, turn the key on again with the engine off. Push the "Erase" button, and the scanner will erase the codes and turn the light on the dash out until the next failure.