Figure 1: Mode $01 "readiness codes" or monitor status.
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OK, I admit it. When it comes to my work, I can be a real "geek." But with the ever-changing technology in this business,
you need to stay current in order to survive.
I've heard both sides on the usefulness of Mode $06 data; I have even played with it from time to time. A recent experience
with a Ford Explorer, however, piqued my curiosity so much I started searching for more information. Allow me to share what
I found out.
SOME BACKGROUND
The first-generation of on-board diagnostics (OBD I) left a lot to be desired, at least from an independent tech's point of
view. Every manufacturer had different data link connectors (DLCs), different communication protocols and different code definitions.
In the early 1990s, legislation was passed to address these issues. The legislation also called for more thorough self-diagnostics
for emissions-related systems – beyond that of simple continuity and pass/fail tests. The Society of Automotive Engineers (SAE) developed guidelines for manufacturers and equipment makers to standardize the DLCs,
code identifiers and communications protocols. They also developed standard diagnostic "modes" in a document referenced as
"SAE J1979." You're already familiar with most, if not all, of them, but let's do a quick review. Note: If you didn't already
know it, the "$" sign denotes the number as a hexadecimal. It's for the computer to understand and really has no impact on
us as techs.)
MODE $01: CURRENT POWERTRAIN DIAGNOSTIC DATA
Figure 2: If the monitors aren't complete, Mode $06 tests may be invalid.
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This mode provides access to "active" data, such as fuel trims, oxygen sensor voltages, engine temperature, etc. Some manufacturers
include more data than required; some don't. Controller Area Network (CAN) vehicles, with their increased capability, typically
show more information than non-CAN vehicles. Mode $01 also displays Malfunction Indicator Lamp (MIL) status as "on" or "off."
If "on," it also will indicate which control module requested the MIL. Last, the on-board monitor status is displayed here
– but more on that later.
MODE $02: POWERTRAIN FREEZE FRAME DATA
If a code is set, the conditions that were present at the time the code was registered are listed here. This information can
give a tech an idea of the operating conditions that were present when the fault occurred.
MODE $03: POWERTRAIN DIAGNOSTIC TROUBLE CODES (DTCS)
We all know this one.
MODE $04: CLEAR/RESET DIAGNOSTIC INFORMATION
This mode clears codes and freeze frame data. It also does one more thing. Remember the on-board monitors I mentioned? They
are also cleared and reset.
MODE $05: OXYGEN SENSOR MONITOR TEST RESULTS
This mode is specific to the on-board testing of the oxygen sensors. On CAN vehicles, it is a part of Mode $06. While it's
not specifically a part of this topic, it's a good tool for checking on the health of the sensors.
MODE $06: LATEST TEST RESULTS FOR NON-CONTINUOUS MONITORS
