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Old 12-19-2009, 09:10 PM   #1
arghx7
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HOW TO: Check if your OBD II car is ready for inspection

I think there's a lot of confusion floating around about what inspection "readiness" really means.

Here's how it works. OBD II was designed to make tailpipe testing unnecessary. Therefore the PCM tests the emissions control systems on its own. The PCM can't always take a "snapshot" of sensor data to know whether a system is working right. It takes time and certain types of driving conditions to know for sure.

The most common/important tests that need to be flagged "Ready" are:

-- Catalytic Converter test: the PCM monitors rear O2 sensor voltage over time to see if your cat is working right

-- Evaporative system: the test that makes you throw a code when the gas cap is loose. EVAP systems are actually crazy complicated.

-- Oxygen sensor: the PCM checks for a particular signal curve over time. The exact test depends on the sensor's position (Front or rear) and whether it is a wide or narrowband sensor. There's also tests for the the O2 sensor heater.

-- EGR system: not many newer cars have this, but you will find it on a lot of early OBD II cars (late 90s).

After you disconnect the battery or clear codes, most of the readiness monitors go to "Not ready." It is a myth that you need to drive x miles for the car to be "ready" for inspection. There's no set number of miles. I've passed inspections after less than 50 miles of driving sometimes. It just depends.

The Do-It-Yourself OBD II Inspection

The best way to determine whether your car is ready for inspection is to hook up to a higher end OBD II scanner if you have one. I have one of the big orange Actron scanners (Actron CP9180) that you usually see being used by auto parts store employees. It was maybe $120 new off ebay when I bought it a while ago.

Now I'm going to demonstrate me checking to see if my car will pass inspection. This is my daily driver, a 1997 Infiniti Q45. My 1988 Rx-7 Turbo doesn't even have a check engine light!



The first shot here is of the main menu in the Actron CP9180. I have two choices. I can select "State OBD Check" to get a summary of my readiness monitors and DTC's. I can also select "I/M Monitors" to get a breakdown of all the readiness checks in the PCM. So first I select "State OBD Check."



From this screen I can see that the check engine light (Malfunction Indicator Light) is not active. I do have one DTC however, but it is a "pending" code that has not yet tripped the MIL. This number could be "3" if I had two active codes and one pending code.

Then the scantool separates my readiness monitors into 3 categores: OK, Incomplete, or Not Applicable. Any 2001+ car must have all but 1 supported monitor set as "OK." Only 1 readiness monitor can be set flagged as "incomplete." This car will pass an inspection because the MIL has not been set and all monitors are ready. Now let's take a more detailed look at my list of readiness monitors in the "I/M Monitors" screen.



Those top three are my continuous monitors. Those three are always active. Any monitor that is not supported is listed as N/A. This particular car has an EGR readiness monitor but it does not have an EVAP monitor.



Any monitor that requires some sort of drive cycle is called a non-continuous monitor. Those are the ones you are waiting on when you visit the inspection station. In my experience the Catalyst monitor and the EVAP monitors take the longest to be set. Here is a drive cycle that may help set the monitors:




I hope that clears up some confusion about OBD II inspections and "readiness" tests. Engines don't just arbitrarily become "Ready" after x number of miles or x number of drive cycles. PCM's go through a series of tests to make sure the components are working, and different criteria must be met for every engine. A lot of inspectors really don't understand this system fully. They just do whatever their inspection tool tells them.
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1999 Toyota Corolla (beater)

Last edited by arghx7; 12-19-2009 at 09:14 PM.. Reason: pics
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Old 12-19-2009, 10:18 PM   #2
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very informative write up. only problem i see with it is most people who have an OBDII scanner, know how to check I/M monitors. the people who dont have OBDII scanner, dont know what the hell I/M monitors are, and i cant justify a normal person going and dropping $100 for a scanner just to know if its ready or not. besides, if a person were willing to go buy a ODBII scanner just to know if its ready or not, they should just buy this:


http://www.ntxtools.com/network-tool...8-p-OTC02.html
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Old 12-19-2009, 10:42 PM   #3
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A scantool of that price level has a lot more than readiness monitor testing. Like many tools, it is an investment.

It can read live data (only at the SAE mandated 5 samples per second rate) and play it back, or give "freeze frame" data from when a fault occured. I have adjusted throttle position sensors and throttle cables using this scantool. I have tested OEM coolant temperature gauges and O2 sensors. I have discovered vacuum leaks from reading MAP sensors. I have tested the health of a car's tune by reading the short and long term fuel trims. You just have to know how to use it, and it helps if you work on a diverse range of cars.

For a lot of people $120 is nothing for a tool. I paid $170 for a coolant pressure tester that will work with any radiator design and it was worth every penny.
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Old 12-19-2009, 10:53 PM   #4
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Quote:
Originally Posted by arghx7 View Post
A scantool of that price level has a lot more than readiness monitor testing. Like many tools, it is an investment.

It can read live data (only at the SAE mandated 5 samples per second rate) and play it back, or give "freeze frame" data from when a fault occured. I have adjusted throttle position sensors and throttle cables using this scantool. I have tested OEM coolant temperature gauges and O2 sensors. I have discovered vacuum leaks from reading MAP sensors. I have tested the health of a car's tune by reading the short and long term fuel trims. You just have to know how to use it, and it helps if you work on a diverse range of cars.

For a lot of people $120 is nothing for a tool. I paid $170 for a coolant pressure tester that will work with any radiator design and it was worth every penny.

i guess i was looking at it from the view points of the customers at my shop who i have to explain all the time to what drive cycles are and when to come back...i usually tell them about a week just to make sure its ready when they come back for an inspection. and yes, i know how the scan tools work, i have 3 myself...and i have invested about $7500 in tools for me this year so i know about being worth the investment.
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Old 12-19-2009, 11:14 PM   #5
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I see what you're saying. That's why the writeup was posted on Horsepower Junkies, not Yahoo! Autos.
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