When considering the diagnosis of DTC’s as they relate to MIL ‘on’ conditions, or reported MIL ‘on’ conditions, many technicians stop short of doing everything they can to identify a potential trouble spot, or to confirm a completed repair. A tool that may often be overlooked is referred to as Mode $06 (which I’ll refer to hereafter as Mode 6). Mode 6 is a function of the Global OBD II aspect of whatever scan tool the technician is using. Mode 6 allows for a more complete analysis of monitor test results.
In the last article we defined DTC’s as the results of a test, or monitor. This is true in the sense that the DTC is a pass/fail result of the test, or monitor, conducted. If the test(s) passed, then there is no DTC, if the test(s) failed, then a DTC is set. Mode 6 data allows the technician to see by how much the test passed or failed by for each test conducted. How is this useful?
Mode 6 data is useful in two ways: firstly, it can be used to identify whether a DTC for something like an EVAP condition was set by a major failure, or a more minor failure. Secondly, it can be used to determine how successful a completed repair was. For instance, when replacing a catalytic converter, you may have made the DTC disappear, but by how much did the monitor pass with the new catalytic converter? Many times an aftermarket converter will allow the monitor to pass, but not by very much. Over a short period of time an inferior converter will become less effective, possibly causing the monitor to fail and creating a comeback. A technician can spot a potential problem by reviewing Mode 6 data to discover by how much a monitor is passing.
Because monitors are run by the engine control computer, they are very logical. Remember, computers only know one thing – voltage. Therefore, monitor results are determined by thresholds. The computer will run a test, and look for a result that is above or below a certain value. The pass/fail logic is rarely more complicated than “if value is above ‘x’ and below ‘y’, then value is deemed acceptable”.
Mode 6 data tells a technician how close to the threshold the monitor result was. By viewing Mode 6 data, the technician can see if the monitor just barely passed, or just barely failed. You might think of it as “did I pass with a 61, or fail with a 59?” By viewing the monitor result in such detail a more detailed diagnosis can be made.
Each scan tool, and for that matter, each manufacturer, will display the Mode 6 data in a slightly different manner. Some manufacturers will display the values in a graphical format with red and green shading depicting the pass/fail zones. Other manufacturers will display data in numerical format.
A common challenge when viewing Mode 6 data, specifically on non-CAN vehicles, is that the data is often presented in hexadecimal format. OE repair information provides for conversion factors so that actual values can be determined by the technician. I personally, am not convinced that you have to do the actual conversions in order for the data to be useful however.
Mode 6 data will provide an actual value, a minimum value (where applicable), and a maximum value (where applicable). Just knowing what these values are, even if you don’t know what the actual units of measurement are, is enough to tell the technician by now much the computer saw the test passed or failed by.
In the last article I presented a case study of a Toyota Corolla with an EVAP code. In this case the vehicle returned to the shop three times before the actual problem was found. The rest of the story was that the vehicle returned a fourth time, at which point it was shipped to the dealership to have yet more parts replaced.
On this particular vehicle, during the third repair attempt, a cracked fuel pump housing was found. The fuel pump assembly was replaced and the vehicle returned to the customer. A week later the vehicle returned yet again with the same P0446 DTC. Had the repair shop test driven the vehicle in such a manner as to complete the EVAP monitor (see previous article), and then reviewed Mode 6 data, it would have been discovered that the monitor had passed, but not by very much (and certainly not by enough to say with confidence that the completed repair was adequate).
When diagnosing a MIL ‘on’ condition, use Mode 6 data to find intermittent problems (monitor passes three times in a row, but not by much, and then fails the fourth test by a little bit), confirm your repair (make sure monitor passes in the middle of its range), or to determine if you’re looking for a major or minor failure. Using Mode 6 data can be a key to fixed right first time…and a happy customer!
Be sure to use the link below to sign up and follow this column! As always, feel free to contact me with questions, concerns, or observations. I can be reached through www.intelligentmechanic.com. May 2012 bring you all peace and prosperity!
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