Craig Truglia is an ASE A6, A8,and L1 certified technician who presently works as a service writer for Patterson Auto Body, a repair facility in Patterson, N.Y. A former shop owner and editor of several automotive repair magazines, Truglia combines his Columbia University education with the real-world experience he sees daily in the automotive repair field. Technicians Truglia and Fred Byron took part in diagnosing the different vehicles in this article.
Mode 6 has been around for many years now. Technicians have often not made much use of it because they find it confusing and often not that informative.
Yet, there are a school of technicians and instructors who think that Mode 6 is the best thing since sliced bread. They boast that it helps quickly diagnose cars and gives us a window into what the software engineers were thinking when they made the criteria for what turns on the Check Engine Light.
For our purposes here, we are going to cover how to read Mode 6 and in the real world, how it helps us diagnose a vehicle. We leave it to you to decide if it is a worthwhile part of your diagnostic arsenal.
Real-world Mode 6
To begin understanding Mode 6, it helps to know exactly what it is: Mode 6 is the criteria that software engineers use to allow us to see the information that causes the Check Engine light to illuminate on a specific vehicle. This means that every single vehicle has different criteria. It is also worth noting that not every vehicle has it, as it only started finding its way into vehicles beginning in the early to mid 2000s.
To help us understand Mode 6, let’s look at a photo capture on a known good 2004 Toyota Prius using the ATS EScan. As we can see, Mode 6 gives us six different sets of data (see Figure 1). The ATS EScan is the only scan tool that not only decodes Mode 6 information, but allows the user to see it all at once. Further, it lets the technicians pick specific Mode 6 tests and update the test results in real-time.
The OBD Monitor ID (OBD MID) tells us what is being tested. The Test ID (TID) tells us what specific test is being run. The Test Value is the actual result of the test. The Min Limit is the minimal allowable test result that will not set a DTC. The Max Limit is the maximum allowable test result that will not set a DTC. So, anything below the Min or above the Max will set a DTC. Units, simply, tells us what unit of measurement is used for the test.
On the Toyota in Figure 1, we can see the Toyota passes all of its tests with flying colors. With the EScan, the Mode 6 Test Values that come close to failing are highlighted in yellow and when they fail, they are red. These are only “ballpark” estimates if something is close to failing, because only the OEM software engineer really knows how close is “real close” for each individual vehicle. It is best only to take a Test Value very seriously if it is above the Max Limit or below the Min Limit.
On most scan tools, you are not going to be able to decode Mode 6. This means you won’t have the TID translated into English for you. If we look at Figure 2, we can see everything, but no TID translations. This is what Mode 6 looks like without the TIDs translated by the EScan.
Keep in mind, most scan tools will neither translate TIDs nor list all of the Mode 6 tests at once. Instead, you will be forced to go into each test in order to get an idea of what the result of each one is. This is so time-consuming, most technicians will just ignore Mode 6 all together. For this reason, if you are serious about wanting to exploit the functionality of Mode 6, it is wise to get a scan tool that makes it quick and usable.
So, when using a regular scan tool, what should you do if you do not know what the TID is? Most of the time you can simply guess. If a MID fails for an oxygen sensor heater, then you know there is some sort of problem with the circuit. Further, if the OBD MID is Cylinder Misfire and you are still counting any misfires since you last deleted the DTCs, it is obvious you did not fix the misfire in that cylinder. Lastly, if you are diagnosing a P0420 and you think you fixed it with a new rear oxygen sensor, you do not need to know what the TID really says in order to know that a low number on Catalyst Monitor Bank 1 is good.
TIDs become most useful when doing an EVAP diagnostic, as they really tell you which part of the EVAP test for the EVAP Monitor failed. But, even then it might not be helpful, because the software engineers do not always tell you exactly what failure will affect the results of which MID.
What can we learn from this? Use your common sense. You can probably figure out what the Mode 6 tells you is failing by looking at the MID alone.
Outside of the misfire counter MID, Mode 6 alone does not tell you everything you need to know anyway, so you will need to use data stream (PIDs) in order to further diagnose the vehicle.