| I have seen many people talk about OBD-II | | | | the check engine light is not on, the car is given a |
| emissions tests on various web forums. Often | | | | pass without needing any further emissions |
| with a puzzled: "I failed readiness!" or "Do I have | | | | related tests. |
| to do an OBD-II test on my 1994 vehicle?" Since | | | | For the car to definitively say that the vehicle is in |
| OBD-II has replaced or will replace sniffer tests | | | | working order it needs to examine its systems |
| for 96 and newer vehicles in most states, I | | | | for a set number of "driving cycles". Driving cycles |
| thought I'd dump some introductory information | | | | are defined differently for different car |
| about OBD-II emissions tests for people. I don't | | | | companies. For some a driving cycle is the time |
| get into the details about OBD-II, the various | | | | between when the key is first turned on, until it is |
| protocols, or how to tune an OBD-II vehicle here. | | | | turned off. For others, it is any 10 minute period |
| Only what to expect in the emissions process. | | | | of non-idle driving, etc. This is where the concept |
| First, some really quick background: California | | | | of readiness is introduced. When the vehicle's ECU |
| required emissions control systems (Catalytic | | | | is reset for any reason (replacement, low battery, |
| converters) on cars sold in California starting the | | | | faulty sensors, etc) it resets the 'readiness |
| 1966 model year. This was adopted across the | | | | monitors' inside the ECU. These are a number of |
| US in 1968, and eventually became the Clean Air | | | | flags that determine whether or not the car is |
| Act of 1970 which required emissions standards | | | | prepared to validate the condition of the |
| that were hard for manufacturers to meet. | | | | emissions systems. The vehicle then must be |
| Ultimately, car makers found that switching to | | | | driven for a preset number of drive cycles to |
| electronically controlled engine management | | | | give the ECU all the information it needs to get |
| allowed them to meet these demands. These | | | | out of the unready state and actually test the |
| electronics became more sophisticated and more | | | | emissions systems. |
| standardized as time went on, and now we have | | | | If a car is inspected while it is not ready, the car |
| a standard protocol (OBD-II) that all these | | | | will return 'not ready' to the inspection computer. |
| computers adhere to. | | | | On cars sold between 1996 and 2000 an |
| Today: Many States, California, Massachusetts, | | | | emissions test is considered a fail if any 2 of the |
| New York, Illinois, Washington, New Hampshire, | | | | emissions systems return not ready. On later |
| and on and on have mandatory emissions | | | | vehicles, you are only allowed one not ready. The |
| inspections in some or all counties. Typically this is | | | | typical remedy for failing readiness is to drive the |
| used as part of the car registration and renewal | | | | car around for up to 500 miles and trying the test |
| process. Up until 2000, this just meant popping | | | | again. After that, if you still fail, a dealer or |
| the car on a dyno, sticking a sniffer in the tailpipe | | | | somebody with factory diagnosis equipment is |
| and measuring what percentage of the air coming | | | | required to force the vehicle to run the emissions |
| out of the vehicle is clean. However, in 2000 the | | | | tests regardless of readiness. |
| EPA started pushing an "OBD-II emissions test" | | | | Modified Cars: OBD-II represents a problem for |
| and many states adopted it, or are in the process | | | | cars with modified emissions systems. In the past, |
| of adopting it. | | | | you could just keep the factory exhaust in a |
| An OBD-II test consists of the emissions | | | | corner of your garage and slap it on for |
| computer plugging into the OBD-ii port on the car | | | | inspection, but now the electric tattle-tails will still |
| (usually under the dash or hidden behind the | | | | catch you. You can use a datalogger, such as the |
| cigarette lighter) and asking the car's computer | | | | car-code logger: to check whether your car has |
| whether the emissions equipment on the vehicle is | | | | passed readiness and thinks it is in an emissions |
| working within the required efficiency limits. This is | | | | happy state. This is of course for use with |
| advantageous over the sniffer because its much | | | | off-road only vehicles only. |
| faster, more consistent (in theory) and harder for | | | | A common problem for modified cars is |
| those of us that like fast cars to just jury rig a | | | | secondary o2 sensors. Part of the OBD-II tests |
| huge catalytic converter the morning before | | | | involves determining the efficiency of catalytic |
| inspection in order to pass with flying colors in our | | | | converter (or pre-cat catalytic converters) by |
| fire-spitting vicious mobiles | | | | checking the value of the oxygen sensors which |
| The way OBD-II tests actually work, is pretty | | | | are located after the cat. If your off-road vehicle |
| simple. The car's ECU waits for a set of conditions | | | | does not have this equipment the vehicle will likely |
| that are representative of normal driving and then | | | | fail. A common solution for this problem is to |
| checks the values of a few sensors to make | | | | install an oxygen sensor simulator which gives the |
| sure that under that condition the equipment is | | | | car's ECU a false signal that mimics what it is |
| working exactly as it should. Typically it examines | | | | expecting to see so it thinks everything is in |
| systems such as the catalytic converter, the | | | | order. A quick internet search for "o2 simulator" |
| Exhaust Gas Recirculation (EGR), and the | | | | will return further information on this topic. |
| evaporative emissions. It stores these results | | | | Finally, remember that you will need to drive the |
| internally and the computer just queries for these | | | | car a lot of miles to get readiness to pass. In |
| results at inspection time. The inspection machine | | | | some extreme cases over 1000 miles is required. |
| also checks the computer to see if any error | | | | So if you are planning on taking the car down for |
| codes are set, and if the check engine light (also | | | | a few months in order to do a long project, and |
| know as a Malfunction Indicator Light (MIL)) is set. | | | | your time for inspection is coming up you are |
| If the tester determines that the emissions | | | | better off getting the vehicle inspected before |
| equipment is in order, there are no internal errors | | | | taking it off the road and resetting the ECU. |
| which the car didn't see fit to tell you about and | | | | |