$06 is one of the nine diagnostic modes that is part of the OBD II
onboard diagnostics system on all 1996 and newer vehicles. As
originally conceived, Mode $06 was not designed for use by technicians.
It was supposed to be “hidden” data used by the OBD II system to detect
faults and set fault codes. It was not supposed to be a readily
accessible scan tool data for analyzing the operation of various
components in the engine management and emission control systems.
Consequently, many older scan tools lacked the capability to access and
display Mode $06 data.
But as time went on, some very tech-savvy
technicians discovered that Mode $06 contained a wealth of diagnostic
information. In fact, it turned out to be the mother lode of diagnostic
information provided you can figure out how to read and use it.
we go any further, we should say that few counter professionals will
ever use Mode $06 to help a customer diagnose a Check Engine light.
Most of the scan tools that parts stores employees typically use to
perform plug-in diagnostic checks on customers’ vehicles are basic code
readers or entry-level scan tools.
So, many of these tools can’t
even access Mode $06. But even if you have a scan tool that has Mode
$06 capability, it’s doubtful you would ever have the need to delve
that far into the on-board diagnostics. That level of troubleshooting
is best left to a professional technician with a lot of experience and
know-how in scan tool diagnostics.
With that said, it’s helpful to
be aware of Mode $06 and how a technician can use it to troubleshoot a
Check Engine light that comes back on after repairs have been made. In
fact, if a technician knows how to use Mode $06 to look for certain
kinds of faults, they can usually keep the Check Engine light out and
prevent unnecessary comebacks.
Mode $06 is often the key to solving
no-code driveability and emission faults, to identifying sensors and
other components that are still operating within acceptable limits but
are on the verge of failure, and for reducing comebacks involving the
catalytic converter, EVAP system and EGR system repairs and engine
WHAT IS MODE $06?
Mode $06 data is information
the OBD II system tracks and compiles on “noncontinuous” monitors. It
is tabulated in hexadecimal code (a base 16 number system that uses
digits 0 to 9 plus letters A through F), which is the computer language
that the PCM uses to manage things. The “$” symbol means the data is in
hex code, not ordinary decimal numbers.
The fact that Mode $06 data
is in hex code means it has to be converted into familiar decimal
values for us to understand it. This requires some math and conversion
factors, or scan tool software that can do the translation for you. You
also need a reference chart from the vehicle manufacturer that
identifies what component or system test each line of code refers to,
and what the acceptable range of values are for that particular test.
Only then can you determine whether or not a particular Mode $06 test
value is good, bad or borderline.
On OBD II systems up to the
introduction of Controller Area Network (CAN) electrical systems, there
are two code identification tags for each line of data. The first is
the Test Identification (TID) that indicates the monitor test, and the
second is the Component Identification (CID) that identifies the sensor
or other component that is being tested. After that come the actual
On CAN vehicles (those from 2003 and newer), the TID
is now called MID for Monitor Identification. It’s the same thing with
a different name. Better yet, the MID test IDs have been standardized
across different vehicle makes and models.
Depending on the the
capabilities and software in the scan tool or scanner software you are
using, the hex code TID and CID values may be translated into plain
English (or Spanish) followed by the hex code or decimal test results,
the range of acceptable values for that particular test, the units of
measure for that test (voltage, pressure, etc.), and a PASS or FAIL
The following is a partial list of the Mode $06 monitor
tests that can be accessed on a late model Ford vehicle with a CAN
MID$01 - Oxygen sensor
MID$02 - Oxygen sensor
MID$03 - Oxygen sensor
MID$05 - Oxygen sensor
MID$06 - Oxygen sensor
MID$07 - Oxygen sensor
MID$21 - Catalyst monitor
MID$22 - Catalyst monitor
MID$31 - EGR monitor
MID$32 - EGR monitor
MID$33 - EGR stepper motor
MID$3A - EVAP monitor
MID$3B - EVAP monitor
MID$3C - EVAP monitor
MID$71 - Air injection monitor
MID$A1 - Misfire monitor
MID$A2 through MID$AB - Misfire monitors for each cylinder
each of these monitor tests are additional subtests of various
components. For example, within the MID$01 oxygen sensor monitor is a
CID$11 O2 sensor switch point test, a CID$80 O2 sensor signal amplitude
test and a CID$81 O2 sensor heater circuit amperage test. Under the
MID$31 EGR monitor there is a CID$80 delta pressure upstream test for
the differential pressure (DPFE) sensor, a CID$81 delta pressure
downstream test, a CID$84 delta pressure EGR leak check test, and a
CID$85 delta pressure EGR flow test.
Each of these tests has an
upper and lower limit that is programmed into the PCM by the
calibration values for that particular year, make and model of vehicle.
The acceptable range of test results for each CID is determined by the
vehicle manufacturer. Cut points are then set to assure emissions
PASS OR FAIL?
As long as all of the
components that are being monitored and tested by the OBD II system
pass, no codes are set and the Check Engine light remains off. If a
component fails a test, it won’t necessarily set a code and turn on the
Check Engine light. It depends on the component that failed the test,
how many times it failed the test (multiple failures may be required
from some tests before OBD II will set a code), and whether or not the
test has actually run because another fault has prevented the test from
An oxygen sensor fault, for example, will prevent any of
the catalyst monitor tests from running. Why? Because the OBD II system
requires reliable inputs from all of the upstream and downstream O2
sensors to check catalyst efficiency. If the vehicle has a bad upstream
or downstream O2 sensor, it can’t compare before and after readings to
calculate converter efficiency. Consequently, an O2 sensor component
test failure will prevent the catalyst monitor from running its tests.
It’s important to keep this in mind when reviewing Mode $06 data
because a failure in one test may prevent other tests from running.
another mystery of Mode $06: Even if a sensor is functioning within the
established limits for a particular CID test, you can’t always assume
the sensor is functioning normally. If it is near the upper or lower
limit of the acceptable test range, it may be enough to cause a
noticeable driveability or emissions problem.
For example, say one
of the oxygen sensors is lazy or is biased rich or lean. It may not be
bad enough to fail its CID tests, but it might be sluggish or biased
enough to throw off the air/fuel mixture, resulting in a loss of fuel
economy, poor throttle response or an engine misfire. That’s why you
need to look closely at the CID test results for that sensor in Mode
$06 so you can see how close the sensor is operating to its upper and
lower limits. If the test results are just within the limits, it would
tell you the sensor is probably causing a problem and will soon fail.
Time to replace it with a new one.
FINDING THE REAL CAUSE
some cases, OBD II may set a fault code for a problem that is being
caused by something else. This includes lean fuel mixture codes,
misfire codes and catalyst efficiency codes. A vehicle cannot pass an
OBD II plug-in emissions test if the Check Engine light is on. You have
to read and clear the code, diagnose the fault and make the required
repairs so all the OBD II monitors will run and pass.
say a vehicle failed an OBD II plug-in emissions test because of a
P0420 catalyst efficiency code. Should you replace the converter, the
oxygen sensors, or what?
Here’s how Mode $06 can help. By looking at
the CID test results data, you can see which catalyst test failed. Then
you can look at the various CID tests for the upstream and downstream
oxygen sensors to see if perhaps one or more sensors are lazy or
biased, and are affecting the test results. In some cases, you may find
the O2 sensors are all functioning well within their normal limits, but
catalyst efficiency is being affected by a crack or pinhole in an
exhaust manifold, Y-pipe or flex pipe ahead of the converter that’s
leaking air into the exhaust.
EVAP codes are always a pain because
EVAP problems can be difficult and time-consuming to diagnose. You can
spend hours with a smoke machine trying to find pinhole leaks when the
real fault may be in the canister purge control solenoid, a vent
solenoid or the fuel pressure sensor in the fuel tank.
Again, you can
use Mode $06 to look at the various EVAP component tests to see why a
particular code might have set. You can also look at the various EVAP
test results to make sure all of the components are well within range
and not operating near their minimum or maximum threshold limits.
OBD II performs a long list of component self-tests, sometimes a test
limit may be set too high or too low, causing codes to set
unnecessarily. For example, a vehicle may be setting a misfire code
repeatedly because the maximum limit for misfires was set too low. The
vehicle manufacturer may revise the limit and offer a new calibration
that can be downloaded and loaded into the vehicle’s PCM. That’s the
beauty of reflashing PCMs. It allows changes in calibration to be
easily updated (assuming you have a J2534 pass-through tool or a scan
tool with flash capabilities).
to watch out for when viewing Mode $06 data are TID/CID tests that
contain old data or bogus data. On some Ford V6 applications, Mode $06
will report misfire rates for cylinders that don’t exist. The CID test
results may show high misfire rates for cylinders 7 and 8. Of course,
there are no cylinders 7 and 8 in a V6. It’s a programming glitch that
OBD II ignores as it monitors misfires. But if you don’t know that, you
may assume the engine has a misfire problem.
The same can apply to
other test lines as well. If the vehicle is not equipped with a
particular sensor or component, there may be bogus data displayed for
that test result.
The bottom line is that Mode $06 is an advanced
diagnostic mode that allows technicians to peer deep into the inner
workings of the OBD II system. It requires a scan tool that can access
and display the TID and CID test results, and an understanding of the
data that is displayed.