Friday, March 18, 2011

Emissions Codes - Decoding the OBDII Diagnostic Code

Emissions Codes - Decoding the OBDII Diagnostic Code

When the "check engine" or "service engine soon" light comes on, it doesn't tell you what or where the trouble is, only that there's trouble. You've connected your scanner towards the automobile laptop or computer and retrieved the OBDII diagnostic code. What does it mean?

The "OBD" of OBDII - often written OBD-II or simply plain OBD2 - stands for On-Board Diagnostics. The "II" is the next generation of emissions standards and codes for those autos bought from the U.S. from 1996 to the present, domestic and imports.

The OBD2 method is mainly for emissions control. Its fundamental components are the catalytic converter and strategically-placed oxygen sensors. These as well as every thing in the car having to complete with engine performance and emissions control are continuously monitored by the vehicle's on-board computer system.

The "check engine" or "service engine soon" light is the signal that there's a challenge with all the vehicle's emissions. The computer has assigned a trouble code towards the issue and fired up the trouble light - technically known as the Malfunction Indicator Lamp (MIL).

When you retrieve the data from the computer via an OBDII diagnostic scanner, it does not tell you the situation directly, such as "timing too slow" or "misfire in cylinder quantity four". What you get is a five-digit alpha-numeric code such as "P0304".

The first digit is really a letter corresponding towards the key method causing the trouble code:

B = Body C = Chassis P = Powertrain U = Network

Another four digits are all numbers. There's by no means instructions "O" in the OBDII diagnostic code. It is the numeric digit zero ("0").


The 2nd digit corresponds towards the sort of code, whether it is the generic standard applying to all OBDII-compliant autos, or a manufacturer-specific code.

0 = Generic codes 1 = Manufacturer-specific codes 2 = Includes both generic and manufacturer-specific codes 3 = Includes both generic and manufacturer-specific codes

The next number corresponds for the sub-system where the problem lies.

1 = Fuel and Air Metering 2 = Fuel and Air Metering (injector circuit malfunction only) 3 = Ignition Program or Misfire 4 = Auxiliary Emission Control System 5 = Automobile Speed Control and Idle Control Program 6 = Personal computer Output Circuits 7 = Transmission 8 = Transmission

So our example trouble code P0304 indicates a challenge within the powertrain. This is a generic code for downside to the ignition method or perhaps a misfire.

The fourth and fifth numbers of the code correspond to the section of the system inducing the trouble. The list of all these sections is long, but you can see the way the final "04" inside our example points to some misfire in cylinder quantity four.

Most OBDII diagnostic scanners include a code library of certain code meanings. A list could also be observed on-line by Googling "obd2 codes list".

You will sometimes find a reference to "Bank 1" or "Bank 2" inside the code explanation. These banks are often meant for "V-type" engines. Bank 1 refers to the side from the engine with all the number 1 cylinder (odd-numbered cylinders). Bank 2 refers back to the side of the engine using the number 2 cylinder (even-numbered cylinders).

A misfire is really a "one-trip" or "type A" issue that on it's own will not switch on the MIL unless it really is severe sufficient to wreck the catalytic converter. A severe misfire will not only turn on the MIL but will signal it to flash at one-second intervals.

Other issues are commonly "two-trip" or "type B" issues. Once the computer initially detects a two-trip problem, it shops the trouble code as "pending". If on the next driving trip the situation has passed, the pending code is erased. But if the issue is there on consecutive trips, the pc will switch on the MIL, alerting the driver to a problem.

The MIL can be persistent. The moment on, it's going to stay on until the challenge is resolved for three driving trips. On the other hand, although the light may go out, the codes be in the computer memory for 40-80 trips depending on the dilemma.

Trouble codes keeping the computer memory will cause a failed emissions inspection if the "check engine" light is on or otherwise not.

Not surprisingly, your diagnostic scanner can turn off the MIL and erase the codes from your computer's memory. This will not do a lot great, nevertheless, when the difficulty recurs immediately after two driving trips and regenerates the trouble codes. The information from the scanner ought to be applied to locate and fix the problem, not only turn off the MIL and erase the codes.


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