What is MIL Status

The MIL status is also known as MIL Readiness and it’s an important factor to passing your emissions test. If your OBDII ECU does not show MIL Readiness or there are at least one condition that is not flagged ready, you won’t pass your smog check. If your OBDII vehicle does not have the MIL status set you will need to complete 2 cycles or two Good Trip conditions to allow your MIL Self Erasure.

Previously in our OBDII FAQ series, we discussed what the Trip Doctor was and how it affects your OBDII freeze frame status. Today we’ll be discussing what conditions set your MIL Readiness so that you can pass your emissions test. Your OBDII statuses are configured and set by what’s known as the Task Manager. This controller is responsible for setting your MIL light as well as checking the test failures.

How do I check my MIL Status?

The Task Manager Screen shows both a Requested MIL state and an Actual MIL state. When the MIL is illuminated upon completion of a test for a third trip, the Requested MIL state changes to OFF. However, the MIL remains illuminated until the next key cycle. (On some vehicles, the MIL will actually turn OFF during the third key cycle) During the key cycle for the third good trip, the Requested MIL state is OFF, while the Actual MILL state is ON. After the next key cycle, the MIL is not illuminated and both MIL states read OFF.

Checking your MIL Status is easy when you have an approved OBDII scan tool. You can rent these at your local auto parts store or purchase one online.


How do my Diagnostic Trouble codes affect my MIL Status?

With an OBDII car there are different DTC faults that have different priorities according to regulations. As a result, the priorities determine MIL illumination and DTC erasure. DTCs are entered according to individual priority. DTCs with a higher priority overwrite lower priority DTCs. Because a stored Diagnostic Trouble code can prevent your MIL status from showing ready, you will need to correct these trouble codes before moving on.

After you are done clearing your OBDII check engine light you will need to complete two Good trip conditions to allow for DTC Self Erasure. What is Self Erasure? With one trip components or systems, the MIL is illuminated upon test failure and DTCs are stored. Two trip monitors are components requiring failure in two consecutive trips for MIL illumination. Upon failure of the first test, the Task Manager enters a maturing code. If the component fails the test for a second time the code matures and a DTC is set.

After three good trips the MIL is extinguished and the Task Manager automatically switches the trip counter to a warm-up cycle counter. DTCs are automatically erased following 40 warm-up cycles if the component does not fail again. For misfire and fuel system monitors, the component must pass the test under a Similar Conditions Window in order to record a good trip. A Similar Conditions Window is when engine RPM is within 375 RPM and load is within 10% of when the fault occurred.

What you need to know about your MIL Status

It is important to understand that a component does not have to fail under a similar window of operation to mature. It must pass the test under a Similar Conditions Window when it failed to record a Good Trip for DTC erasure for misfire and fuel system monitors.

DTCs can be erased anytime with a DRB III. Erasing the DTC with the DRB III erases all OBD II information. The DRB III automatically displays a warning that erasing the DTC will also erase all OBD II monitor data. This includes all counter information for warm-up cycles, trips and Freeze Frame.

How to complete trip cycles

The Trip cycle is essential for running monitors and extinguishing the MIL. In OBD II terms, a trip is a set of vehicle operating conditions that must be met for a specific monitor to run. All trips begin with a key cycle.

Different styles of Good Trip cycle

  • Global Good Trip
  • Fuel System Good Trip
  • Misfire Good Trip
  • Alternate Good Trip (appears as a Global Good Trip on DRB III Scan Tool

Have any questions about this MIL Status FAQ sheet? leave me a message below and let us know.

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