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Passing OBDII emissions (1996-Present Miata)

Depending on your local area laws, you may need to pass an OBDII emissions test.  These are the requirements for our home state of Texas living in a county that requires emissions testing. 

What systems are checked during the OBDII test?
The On-Board Diagnostics (OBDII) emissions test for 1996 & newer vehicles consists of the following:

  • Check 1 - Malfunction Indicator Lamp (MIL) or Service Engine Soon Light, Check Engine Light, Check Engine Symbol check
    This is considered the bulb check portion of the test. The light must come on when the ignition is turned to the ON position and the light must go OFF when the engine is started. The inspector answers these two bulb check questions as either a PASS or FAIL. If the light is not working, the vehicle will FAIL the test, because the purpose of the light is to alert the driver of the vehicle that there is a problem with the OBDII system (exceeding emissions) and the vehicle needs to be diagnosed and repaired.
  • Check 2 - MIL Command Status and Diagnostic Trouble Codes (DTC's) check 
    If the MIL command status is ON, then the vehicle's Powertrain Control Module (PCM) is commanding the MIL to turn ON, because a problem has been detected within the OBDII system and a DTC has been set. 
    For example, an engine misfire DTC - PO301. If the MIL command status is ON with a DTC set, the vehicle will fail. If the OBDII system is operating properly, the MIL command status will be OFF.
  • Check 3 - OBDII (Non -Continuous) 
    Readiness Monitors check

    These monitors are like self checks of each emissions component (EGR, O2 sensor, etc) within the OBDII system. These non-continuous monitors are considered READY until either DTC's have been cleared with a scan tool or if battery power has been disconnected, then the monitors will reset back to NOT READY. 

    In order to get the monitors set back to READY, the vehicle must be driven through a drive cycle, which is a combination of city/highway driving for a set period of time. This drive cycle relearns the OBDII system and rechecks all of the emissions component's individual systems. As each system completes its own self test, the monitor will set back to Ready.

    Effective October 15, 2008:

    For vehicles year model 2001 and newer, we allow one (1) non-continuous monitor to be NOT READY and still pass the test, but two (2) or more NOT READY's will cause the vehicle to fail.

    For vehicles year model 1996 – 2000, we allow two (2) non-continuous monitors to be NOT READY and still pass the test, but three (3) or more NOT READY's will cause the vehicle to fail.
    There are three (3) continuous monitors that are always Ready: Misfire, Fuel System, and Comprehensive Components. If you look at your Vehicle Inspection Report (VIR), you will see the emissions monitors listed and their Ready/Not Ready status. If any of the non-continuous monitors say N/A (Not Available) or N/S (Not Supported), then there is no monitor for that system. 
To recap, lets say you' ve either recently disconnected the battery or cleared a MIL.  This will cause all the sensors listed in Check 3 above to show as NOT READY.  Providing you've repaired the cause of any MIL you will need to drive the vehicle until all your sensors show READY.  Note: In Texas, we are allowed (one) NOT READY monitor on 2001 and newer vehicles and (two) NOT READY monitors on 1996-2000 vehicles.  Check your local laws for what is required in your area. 

Now most mechanics will just tell you to just drive the car and bring it back.  This vague answer may not allow you meet the various scenarios to have the sensors switch back to READY. 

At Track Dog Racing, we've found the following drive cycle have been very successful to reset the sensors in short order.  

Mazda drive cycle:  

Pre-requisites: MIL off and no DTCs present (this is where clearing your codes comes in); fuel level between 15 and 85%; all accessories OFF; cold start (preferred 8 hour cold soak w/ engine between 68 and 86 deg F at start-up)

 

1) Start vehicle and idle 5 min.

2) Rev engine in neutral or park to 2300-2700 rpm for 15 seconds

3)Rev engine in neutral or park to 3800-4200 rpm for 15 seconds

4)Idle engine for 20 seconds with cooling fan stopped. 

5)Accelerate to 52-55 mph, maintain speed (in high gear) for 1 1/2 minutes

6) Decelerate to 15 mph, and then drive for 13 minutes at speeds ranging from 15 to 35 mph

7) maintain steady 25 mph for 50 seconds.

 

Each step of the drive cycle indicates a test for a different monitor on the vehicle (catalyst, o2 sensor, evap, etc) so each step is important. Some vehicles are a pain and may require a few drive cycles. 

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