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 hooked up your scanner to the vehicle computer and retrieved the OBDII diagnostic code. What does it mean?

The "OBD" of OBDII - sometimes written OBD-II or just plain OBD2 - stands for On-Board Diagnostics. The "II" is the next generation of emissions standards and codes for all vehicles sold in the U.S. from 1996 to the present, domestic and imports.

The OBD2 system is primarily for emissions control. Its basic components are the catalytic converter and strategically-placed oxygen sensors. These as well as everything in the vehicle having to do 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 is a problem with the vehicle's emissions. The computer has assigned a trouble code to the problem and turned on the trouble light - technically called the Malfunction Indicator Lamp (MIL).

When you retrieve the information from the computer via an OBDII diagnostic scanner, it doesn't tell you the problem directly, such as "timing too slow" or "misfire in cylinder number four". What you get is a five-digit alpha-numeric code such as "P0304".

The first digit is a letter corresponding to the main system causing the trouble code:

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

The next four digits are all numbers. There is never a letter "O" in the OBDII diagnostic code. It is the numeric digit zero ("0").

The second digit corresponds to the type of code, whether it is the generic standard applying to all OBDII-compliant vehicles, 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 third number corresponds to the sub-system where the problem lies.

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

So our example trouble code P0304 indicates a problem in the powertrain. It is a generic code for trouble with the ignition system or a misfire.

The fourth and fifth numbers of the code correspond to the section of the system causing the trouble. The list of all these sections is long, but you can see how the final "04" in our example points to a misfire in cylinder number four.

Most OBDII diagnostic scanners will come with a code library of specific code meanings. A list may also be found on-line by Googling "obd2 codes list".

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

A misfire is a "one-trip" or "type A" problem that by itself will not turn on the MIL unless it is severe enough to damage the catalytic converter. A severe misfire will not only turn on the MIL but will signal it to flash at one-second intervals.

Other problems are usually "two-trip" or "type B" problems. When the computer first detects a two-trip problem, it stores the trouble code as "pending". If on the next driving trip the problem has passed, the pending code is erased. But if the problem is still there on consecutive trips, the computer will turn on the MIL, alerting the driver to a problem.

The MIL can be persistent. Once on, it will stay on until the problem is resolved for three driving trips. However, though the light may go out, the codes remain in the computer memory for 40-80 trips depending on the problem.

Trouble codes remaining in the computer memory will cause a failed emissions inspection whether the "check engine" light is on or not.

Of course, your diagnostic scanner can turn off the MIL and erase the codes from the computer's memory. This will not do much good, however, if the problem recurs after two driving trips and regenerates the trouble codes. The information from the scanner should be used to locate and fix the problem, not just turn off the MIL and erase the codes.

Emissions Codes - Decoding the OBDII Diagnostic Code

OBDII Vehicles

Emissions Codes - Decoding the OBDII Diagnostic Code

Emissions Codes - Decoding the OBDII Diagnostic Code
Emissions Codes - Decoding the OBDII Diagnostic Code

OBDII Vehicles

Emissions Codes - Decoding the OBDII Diagnostic Code

Emissions Codes - Decoding the OBDII Diagnostic Code

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Emissions Codes - Decoding the OBDII Diagnostic Code

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Emissions Codes - Decoding the OBDII Diagnostic Code

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DM-200 OBDII Wins 2 Major SEMA Awards

DM-200 OBDII Wins 2 Major SEMA Awards

Video Clips. Duration : 3.40 Mins.

DM-200 OBDII Wins 2 Major SEMA Awards
Paul Lowchareonkul, President and CEO of PLX Devices Inc. receives 2 major SEMA 07 awards for the DM-200 OBDII for Best New Interrior Accessory and Best New ...
DM-200 OBDII Wins 2 Major SEMA Awards

DM-200 OBDII Wins 2 Major SEMA Awards

DM-200 OBDII Wins 2 Major SEMA Awards



DM-200 OBDII Wins 2 Major SEMA Awards

What Actually Happens During An OBDII Emissions Inspection

I have seen many people talk about OBD-II emissions tests on various web forums. Often with a puzzled: "I failed readiness!" or "Do I have to do an OBD-II test on my 1994 vehicle?" Since OBD-II has replaced or will replace sniffer tests for 96 and newer vehicles in most states, I thought I'd dump some introductory information about OBD-II emissions tests for people. I don't get into the details about OBD-II, the various protocols, or how to tune an OBD-II vehicle here. Only what to expect in the emissions process.

First, some really quick background: California required emissions control systems (Catalytic converters) on cars sold in California starting the 1966 model year. This was adopted across the US in 1968, and eventually became the Clean Air Act of 1970 which required emissions standards that were hard for manufacturers to meet. Ultimately, car makers found that switching to electronically controlled engine management allowed them to meet these demands. These electronics became more sophisticated and more standardized as time went on, and now we have a standard protocol (OBD-II) that all these computers adhere to.

Today: Many States, California, Massachusetts, New York, Illinois, Washington, New Hampshire, and on and on have mandatory emissions inspections in some or all counties. Typically this is used as part of the car registration and renewal process. Up until 2000, this just meant popping the car on a dyno, sticking a sniffer in the tailpipe and measuring what percentage of the air coming out of the vehicle is clean. However, in 2000 the EPA started pushing an "OBD-II emissions test" and many states adopted it, or are in the process of adopting it.

An OBD-II test consists of the emissions computer plugging into the OBD-ii port on the car (usually under the dash or hidden behind the cigarette lighter) and asking the car's computer whether the emissions equipment on the vehicle is working within the required efficiency limits. This is advantageous over the sniffer because its much faster, more consistent (in theory) and harder for those of us that like fast cars to just jury rig a huge catalytic converter the morning before inspection in order to pass with flying colors in our fire-spitting vicious mobiles

The way OBD-II tests actually work, is pretty simple. The car's ECU waits for a set of conditions that are representative of normal driving and then checks the values of a few sensors to make sure that under that condition the equipment is working exactly as it should. Typically it examines systems such as the catalytic converter, the Exhaust Gas Recirculation (EGR), and the evaporative emissions. It stores these results internally and the computer just queries for these results at inspection time. The inspection machine also checks the computer to see if any error codes are set, and if the check engine light (also know as a Malfunction Indicator Light (MIL)) is set. If the tester determines that the emissions equipment is in order, there are no internal errors which the car didn't see fit to tell you about and the check engine light is not on, the car is given a pass without needing any further emissions related tests.

For the car to definitively say that the vehicle is in working order it needs to examine its systems for a set number of "driving cycles". Driving cycles are defined differently for different car companies. For some a driving cycle is the time between when the key is first turned on, until it is turned off. For others, it is any 10 minute period of non-idle driving, etc. This is where the concept of readiness is introduced. When the vehicle's ECU is reset for any reason (replacement, low battery, faulty sensors, etc) it resets the 'readiness monitors' inside the ECU. These are a number of flags that determine whether or not the car is prepared to validate the condition of the emissions systems. The vehicle then must be driven for a preset number of drive cycles to give the ECU all the information it needs to get out of the unready state and actually test the emissions systems.

If a car is inspected while it is not ready, the car will return 'not ready' to the inspection computer. On cars sold between 1996 and 2000 an emissions test is considered a fail if any 2 of the emissions systems return not ready. On later vehicles, you are only allowed one not ready. The typical remedy for failing readiness is to drive the car around for up to 500 miles and trying the test again. After that, if you still fail, a dealer or somebody with factory diagnosis equipment is required to force the vehicle to run the emissions tests regardless of readiness.

Modified Cars: OBD-II represents a problem for cars with modified emissions systems. In the past, you could just keep the factory exhaust in a corner of your garage and slap it on for inspection, but now the electric tattle-tails will still catch you. You can use a datalogger, such as the car-code logger: http://www.obd-2.com/ to check whether your car has passed readiness and thinks it is in an emissions happy state. This is of course for use with off-road only vehicles only.

A common problem for modified cars is secondary o2 sensors. Part of the OBD-II tests involves determining the efficiency of catalytic converter (or pre-cat catalytic converters) by checking the value of the oxygen sensors which are located after the cat. If your off-road vehicle does not have this equipment the vehicle will likely fail. A common solution for this problem is to install an oxygen sensor simulator which gives the car's ECU a false signal that mimics what it is expecting to see so it thinks everything is in order. A quick internet search for "o2 simulator" will return further information on this topic.

Finally, remember that you will need to drive the car a lot of miles to get readiness to pass. In some extreme cases over 1000 miles is required. So if you are planning on taking the car down for a few months in order to do a long project, and your time for inspection is coming up you are better off getting the vehicle inspected before taking it off the road and resetting the ECU.

What Actually Happens During An OBDII Emissions Inspection

OBDII Vehicles

What Actually Happens During An OBDII Emissions Inspection

What Actually Happens During An OBDII Emissions Inspection
What Actually Happens During An OBDII Emissions Inspection

OBDII Vehicles

What Actually Happens During An OBDII Emissions Inspection

What Actually Happens During An OBDII Emissions Inspection

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What Actually Happens During An OBDII Emissions Inspection

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Global OBD II Modes and Monitors: After Hours, 7-24-2012

Global OBD II Modes and Monitors: After Hours, 7-24-2012

Video Clips. Duration : 45.17 Mins.

Global OBD II Modes and Monitors: After Hours, 7-24-2012
Join our online community for more great resources at workshop.search-autoparts.com. It's free! Every second and fourth Tuesday, technical editor Pete Meier hosts "Motor Age After Hours". This informal webcast features special guests most of the time, but once in a while it's just you and Pete. In this episode, Pete explains what OBD II monitors are, and how to use that information in your troubleshooting. He also covers the 10 modes of OBD II automotive onboard diagnostics and what each offers in completing a successful repair.
Global OBD II Modes and Monitors: After Hours, 7-24-2012

Global OBD II Modes and Monitors: After Hours, 7-24-2012

Global OBD II Modes and Monitors: After Hours, 7-24-2012

Global OBD II Modes and Monitors: After Hours, 7-24-2012

Your Vehicle's Sensors - How to Test Some of Them

After you retrieve the trouble codes from your vehicle's on-board computer, you can now check the sensors. Always refer to your service manual for specifications on your make and model vehicle.

The first trouble code to check is the throttle position sensor (TPS). The TPS is located either on the side of the carburetor or the side of the fuel injected models. It is attached to the throttle body. Visually inspect the sensor for worn insulation on the wires and a loose or cracked connection. Disconnect the sensor.

With the digital volt ohm meter or DVOM in the 20K ohm position, connect the positive DVOM lead to the sensor's center terminal. Connect the negative DVOM lead to one of the other sensors' terminals. Slowly move the throttle lever until it is at the wide-open position. Depending upon which terminal you connected the negative DVOM lead to, the DVOM reading should either increase or decrease steadily. Release the throttle lever slowly. If the DVOM reading is not gradual and steady, but moves instead at an irregular pace, the sensor is defective and should be replaced. Re-connect the sensor. Clear the trouble codes from the ECM memory by disconnecting the negative battery cable for at least ten seconds.

Your next trouble code indicates a mass air flow (MAF). The MAF sensor is located between the air cleaner and engine throttle body. To test, start the engine. Take a screwdriver handle and tap the MAF lightly several times on the plugin side. DO NOT STRIKE THE SENSOR WITH FORCE, IT MAY CRACK. If the engine staggers, misfires, or stops running, the sensor is defective and should be replaced. Clear the trouble codes from the ECM memory by disconnecting the negative battery cable for at least ten seconds.

Start the oxygen sensor performing test by removing the sensor from the vehicle. The oxygen sensor is located either in the exhaust manifold or the exhaust pipe. Visually inspect the sensor for worn insulation on the wire and a loose connection. Start the engine and let it run for about five minutes, then turn the engine off. Disconnect the sensor. Secure the sensor connector away from the exhaust manifold; tape the connector to the fender well, if possible. Turn the digital vote ohm meter to the millivolt setting, connect the positive DVOM lead into the sensor connector terminal, and ground the negative DVOM lead to an unpainted ground. Restart the engine. Observe the DVOM reading. It should fluctuate between 100 and 1,000 mv (0.1 and 1.0 volts). If the voltage does not fluctuate in the pattern indicated above, the oxygen sensor is faulty and should be replaced. Re-connect the sensor. Clear the trouble codes from the ECM memory by disconnecting the negative battery cable for at least ten seconds. Do not set the digital volt ohm meter on the ohm meter setting to do so will damage the oxygen sensor.

The next trouble code indicates manifold air pressure (MAP) sensor. The MAP sensor is usually located on the firewall or the fender well. Visually inspect the vacuum hose and sensor connector for deterioration or loose connections then disconnect the sensor. Connect a jumper wire from terminal A on the MAP sensor to terminal A on the connector. Using a second jumper wire, connect the terminal in the same way. Turn the ignition switch on. DO NOT START THE ENGINE. With the digital volt ohm meter (DVOM) in the 20-volt DC setting, connect the positive DVOM lead to terminal B on the MAP sensor. Ground the negative DVOM lead to an unpainted ground. Observe the reading; it should be between 4.5 and 5 volts. Start the engine, let it idle. Keep the engine at idle and repeat the previous step. If it does not change from the ordinal ones, the sensor is faulty and should be replaced. Reconnect the sensor. Clear the trouble codes from the ECM memory by disconnecting the negative battery cable for at least ten seconds.

This is how to test some of the sensors on a vehicle. There are many more sensors on a car. There are other ways to test them depending on the make and model of the vehicle. When you get ready to retrieve trouble codes or test your sensors, always check the service manual for specifications and how to test your sensors.

Your Vehicle's Sensors - How to Test Some of Them

OBDII Vehicles

Your Vehicle's Sensors - How to Test Some of Them

Your Vehicle's Sensors - How to Test Some of Them
Your Vehicle's Sensors - How to Test Some of Them

OBDII Vehicles

Your Vehicle's Sensors - How to Test Some of Them

Your Vehicle's Sensors - How to Test Some of Them

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How to set Ignition timing: OBD2 Honda/Acura

How to set Ignition timing: OBD2 Honda/Acura

Tube. Duration : 5.35 Mins.

How to set Ignition timing: OBD2 Honda/Acura
this is how you set ignition timing on an obd2 honda/acura. The car in the video is my 2000 integra gsr with a jdm b18c and a bad exhaust leak
How to set Ignition timing: OBD2 Honda/Acura

How to set Ignition timing: OBD2 Honda/Acura

How to set Ignition timing: OBD2 Honda/Acura

How to set Ignition timing: OBD2 Honda/Acura

Your Vehicle's Sensors - How to Test Some of Them

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Innovate Motorsports LM-2 Wideband Air/Fuel Ratio Meter Install & Test

Innovate Motorsports LM-2 Wideband Air/Fuel Ratio Meter Install & Test

Video Clips. Duration : 6.12 Mins.

Innovate Motorsports LM-2 Wideband Air/Fuel Ratio Meter Install & Test
The LM-2 combines an air/fuel ratio meter, a full-function 32-channel datalogger, and powerful software to deliver a complete tuning workshop for less than the cost of one dyno day. Whether you have a piggy-back fuel controller, race carb, aftermarket ECU, ODB-II tuning software, or a flash/chip programmer, an LM-2 is the tool you need to dial in maximum HP. The meter's award-winning digital signal processing technology provides data on exactly how rich or lean an engine is running at any load. The LM-2's self-calibrating circuitry also compensates for changes in temperature, altitude, and sensor condition. -Patented "Direct Digital" Wideband Technology -Wideband O2 Compatible with ALL fuel types -Single or Dual Channel Version Available -OBD-II Scan tool- read/clear DTCs and log up to 16 channels of CAN OBD-II Data -Log directly to SD card (included) -Playback log data on screen and/or with powerful LogWorks software (included) -Large high-contrast graphics LCD -Built-in RPM converter (direct frequency or with optional inductive clamp) 4 fully-differential analog inputs -2 configurable linear analog outputs -Positive lock connectors for all connections -Innovate MTS serial IN and OUT -USB connection to your PC The LM-2 also features two fully programmable linear analog outputs to connect to analog gauges, dyno computers, ECUs, piggyback controllers, and other devices with analog inputs. Analog output 1 comes setup from the factory ready for narrowband simulation; analog ...
Innovate Motorsports LM-2 Wideband Air/Fuel Ratio Meter Install & Test

Innovate Motorsports LM-2 Wideband Air/Fuel Ratio Meter Install & Test

Innovate Motorsports LM-2 Wideband Air/Fuel Ratio Meter Install & Test

Innovate Motorsports LM-2 Wideband Air/Fuel Ratio Meter Install & Test