Mode $06: A Tech's Perspective - Opinions on the usefulness of Mode $06 vary greatly. Let's look at it together and then decide. - Search Auto Parts | Automotive News
First, a word on the on-board monitors. Simply put, an OBD II "monitor" (with the exception of the Comprehensive Component
monitor) is a test of a particular emissions-related system that's operated by the Powertrain Control Module (PCM).
Some monitors run all the time, such as fuel system, misfire detection and comprehensive components and are called "continuous
monitors." Others run only once per drive cycle, including EGR, EVAP and catalyst efficiency. These are the "non-continuous
monitors." As mentioned earlier, Mode $01 shows the status of these monitors, typically as "ready" or "not ready," or "complete"
or "not complete," depending on the scan tool. See Figure 1.
Figure 4
Each of these monitors is composed of a number of individual tests. Mode $06 is where you'll find the results and standards
for these tests. In 2002, regulations were passed that also required some misfire monitor test results to be included in Mode
$06, effective in the 2004 or 2005 model-year. You will find these results on those vehicles that went to the CAN protocol
in those model years. Keep in mind that Mode $06 is a little different with CAN than it is with pre-CAN models.
MODE $07: LATEST TEST RESULTS FOR CONTINUOUS MONITORS
Some scan tools refer to Mode $07 as "DTCs detected during last drive cycle" or "Pending DTCs." Many codes are now two-trip
codes, requiring them to be present on two consecutive monitors in order to turn on the MIL. This allows the PCM to ensure
there is a problem and avoid false MILs. While you won't find individual test results like you do in Mode $06, a failed continuous
monitor will log a "pending" code that you will find here. Also, the same regulations that require misfire reporting in Mode
$06 also require non-continuous monitor pending codes to be reported in Mode $07.
A quick note on two-trip codes. Many non-continuous monitor failures are two-trip codes. Because these monitors only run once
per drive cycle, it will take two completed, consecutive drive-cycles with the monitor involved to trigger the MIL.
This is a consideration especially for EVAP monitors, where they will often not complete on a given drive-cycle because all
the conditions were not met. An EVAP code can be "pending" for several trips and waiting for the second consecutive monitor
to complete.
Figure 5
Continuous monitors, on the other hand, run all the time and will turn on a two-trip code on consecutive drive cycles if that
failure is noted during monitor operation. With the exception of misfire or fuel trim codes, the MIL will turn off if three
consecutive monitors are completed with no failure noted. Misfire and fuel trim codes must be retested under the same conditions
three times before the MIL will turn off.
MODE $08: BIDIRECTIONAL COMMUNICATIONS FOR ON-BOARD TESTING
Peter Meier is an ASE-certified Master Technician, member of iATN and full-time tech in Tampa, Fla. His experience reaches back over 30 years, and his contributions to Motor Age reflect a wide variety of experience with almost every make and model.
Articles by Peter F. Meier
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