February 2005
OBD-II. I'm sure everyone has heard of the word or abbreviation. What exactly is it? What does it do? All cars currently being built use this system and today we will go into detail to show you what it is, how it works, and if it inhibits or promotes modifications to your car.
OBD-II stands for on-board diagnostics and they are standard on all vehicles manufactured today. In the late 1970s, auto manufacturers began using electronics or computers to monitor and control powertrain functions. This was done as a way to control emissions on new cars to comply with government standards. OBD-II is a set of standards and practices created by the Society of Automotive Engineers (SAE), which was approved by the EPA and CARB for implementation by 1/1/1996. Every car built since 1/1/1996 has OBD-II and actually manufacturers began implementing it on certain models as early as 1994. Some of these vehicles were not 100% compliant, but it was a way for the manufacturers to begin getting acquainted with the new system.
The computer reports to the driver if it encounters a "problem". The "problem" is relayed to the driver by way of a MIL. MIL stands for malfunction indicator light, commonly known to drivers as the "Check Engine" light. There are three types of signals the computer will send to notify the driver. The light will flash occasionally if a momentary problem occurs. If the light comes on and stays on, this is a more serious issue and most likely will affect the emissions or safety of the car. When the light starts flashing, this is evidence of a serious problem and the vehicle should be taken to a repair facility immediately. The powertrain control module, or computer, will store the conditions the vehicle was experiencing when the error occurred; this is known as a "freeze frame." The "freeze frame" will store the speed, tachometer speed and other data to help the technician see what type of driving the car was experiencing when the error occurred.
The creation of OBD-II makes it easier on the technician and repair shop. Instead of needing multiple scan tools to diagnose vehicles, they are able to use one with multiple software. Older vehicles have the diagnostic connector in various locations such as under the hood, under the carpet, or under the dash. Reading the codes was different on older vehicles, on 80's Chrysler vehicles you had to cycle the key off-on-off-on-off-on and the Check Engine Light would blink to signify the codes. On Honda's, you had to lift up the passenger side carpet and watch the blinking LED on the computer to get the codes. With OBD-II, the diagnostic connector is the same and is always located on the driver side under the dash.
In the early days of OBD-II, many performance enthusiasts were afraid that the OBD-II system would not allow for the modification of the engine to the specs and power that they desired. It may have been the case had it not been for the intervention of SEMA. SEMA worked with the manufacturers to develop the program, therefore protecting their industry. OBD-II is designed to allow cars to run cleaner and more efficient and it does just that. Newer cars emit less emissions and have more horsepower than cars before OBD-II.
In the current market there are also products available through the aftermarket that will allow owners to check their own codes and view the data list themselves. These products were created to save the consumer money as repair shops charge a labor charge just to hook up the scan tool and view the diagnostic trouble codes. One such product is the AutoTap (www.autotap.com), which makes a program for Windows or for your Palm Pilot. This software allows the user to view sensor data in real-time to know what their car is doing at that moment.
If my Check Engine light is lit, is my car losing power? The answer is no. Check Engine light will primarily light if the PCM recognizes an error that will cause an emissions problem. These errors will not alter the fuel, spark or boost of the vehicle; therefore you may not experience a drivability problem. OBD-II can also keep your vehicle drivable in problem situations known as limp-home mode. In the old days, if a misfire occurred, fuel being dumped in the exhaust and not being ignited would wreak havoc on the catalytic converter and cause it to overheat. With OBD-II, the PCM can recognize the misfire and shut off fuel to the injector to prevent damage to the converter. On OBD-II systems there is a data table that the PCM will use to determine fuel, spark, timing, etc. It uses inputs from various engine sensors to control this mixture. In this system, if one sensor goes bad the data table can eliminate its input from its formula and use a base setting to determine the fuel and spark settings.
Aftermarket products can cause for Check Engine lights to light. This is only caused by products improperly installed or manufactured. We have heard stories about the Check Engine Light illuminating when swapping out exhausts or intakes, but these codes being set will not affect your power output. This is typically caused by the premature release of a product without the proper research and development.
Let's take a look at how an actual OBD-II code breaks down. A sample OBD-II code is P0105. Each digit in this code means something. The first digit is the system: P for Powertrain, B for Body, C for Chassis and U for Network. The second digit is either a 0 or a 1. The zero is an OBD code, one is a proprietary code. The third digit is the subsystem of the main system, in this case the powertrain: 1 is for fuel/air metering, 2 is for fuel/air metering(injectors), 3 is for ignition system, 4 is auxiliary emission control, 5 is for computer output, and 6 and 7 are for transmission. The last two digits signify the fault code. Therefore, this code is a powertrain code, an OBD code, subsystem is fuel/air metering and the 05 is the fault code.
Today, we have covered many of the basics related to the OBD-II system. Now you know how the diagnostic system in your vehicle operates. So next time your car has a Check Engine light on, you will know the story behind it and how to check and clear it if you so desire. If you have further interest in this system, please view http://www.obdii.com.
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Jason Helferich
www.streetstylecustoms.com
