The more one knows, the more you realize how little one knows! Working with cars is often a humbling experience as you learn something you did not know almost daily. When it comes to scan data and its interpretation, it can be the difference between making a profit that day and losing enough money and sanity to make you question why anyone would get into this business. OBD II has been around since the mid-1990s. Several years ago, I wrote an article on a hidden feature in most scan tools called Mode 6. The article explained what Mode 6 was and where one goes to find the information that may help you diagnose the “problem child” you have sitting in your stall.
The automotive manufacturers established several different scan tool diagnostic modes to comply with the SAE J1979 OBD II standards. Many of the modes you use daily, but you may be unaware that they were implemented to meet the J1979 government standard. Information such as the Exhaust Gas Sensor Monitor, Catalyst Monitor, EGR Monitor, VVT Monitor, EVAP Monitor, Exhaust Gas Sensor Heater Monitor, Heated Catalyst Monitor, Secondary Air Monitor, Fuel System Monitor, Boost Pressure Control Monitor, NOx Adsorber Monitor, NOx/SCR Catalyst Monitor, Misfire Cylinder Data, PM Filter Monitor are likely part of the Mode 6 data monitor systems on your OBD II application.
J1979 scan tool modes include:
- Mode 01 – Data stream (sensor readings, switch status, output commands)
- Mode 02 – Freeze frame data (if DTCs are present) as well as failure records on some applications.
- Mode 03 – Diagnostic Trouble Codes
- Mode 04 – Clear codes and freeze frame data
- Mode 05 – Oxygen sensor monitor
- Mode 06 – Non-continuous monitors (EVAP, catalyst, EGR, to name a few)
- Mode 07 – Continuous monitors (Misfire, Electrical circuits as examples)
- Mode 08 – Bidirectional communication (onboard tests and control)
- Mode 09 – Vehicle VIN, PCM calibration, etc.
Mode 6 is one of the least known standards as it was designed as an engineering feature, not a feature designed to aid service. Through the years, technicians have discovered that Mode 6 information can be of great value, especially when diagnosing intermittent concerns or when one wants to monitor just how close the system you are monitoring is to setting a DTC.
In the old days, the Mode 6 information was displayed in a ‘hexadecimal” format, and you had to have a “cheat sheet” to interpret the values shown. The Mode 6 data was displayed in 3 columns: TID (Test Identification), CID (Component identification), and a column that identified if the test that ran had passed or failed. This means you would see data displays like TID $07, which represented the hex values for the O2 sensor monitor, or CID #90, which represented the O2 sensor heater amperage. In the old days, to find the Mode 6 information on your scan tool, you may have been required to choose your scanner’s “enhanced” mode to see the information the computer was recording. Confusing, I know, and that is why many technicians never really got into the whole Mode 6 thing. Nowadays, it is much simpler as the scan tool will typically decipher the Hex values and display the information in simple terms known as flags or IM test monitors.
So, you are probably wondering how to use this feature to help with the car setting in your stall right now. Three things come to mind:
- Many times, you want to verify the repair. Mode 6 testing indicates when the system in question is being tested and what its test results were, pass or fail.
- Many vehicles will display the parameters for the IM test being conducted. In addition, you may also have the specifications for the DTC related to that test shown. That information lets you see how close your vehicle is to setting a DTC. If you had a vehicle whose values were at the edge of the specifications for setting a code, the vehicle may not set the DTC. But the DTC will set as soon as there is a slight change in the values. This means that you now have an intermittent DTC to deal with. By monitoring the actual values you see for the IM monitor in question, you can anticipate when/if a DTC is likely to set.
- GM, Ford, and many others provide the MODE 6 data for each of the ECM/TCM DTCs for the specific vehicle you are working on. Some, like Ford and GM, provide the information for free, while others require you to pay for access. Having access to this information is invaluable as it tells you exactly what the controller is looking for to set the DTC.
GM is easy to access using the GM parts website (gmparts.com). Simply click on the “technical recourses” tab and then the Mode 6 data tab. This will take you to a matrix showing the years. Click on the year and select either the engine or transmission. On later applications, you will need to open the “diagnostic parameter file matrix” to determine which file will access your vehicle information. Once you have determined which file should be opened, click on the file, and the MODE 6 DTC matrix will open. Scroll through the DTC’s until you locate the DTC in question. The information displayed represents the information the controller uses to set the DTC in question. Figures 1 through 4 are examples of the website pages.
Ford also uses the official Ford service website at motorcraftservice.com. Choose your country and language. Select the “free resources,” then the OBD II theory and operations tab, and finally, the application you desire to review. Figures 5 and 6 show these website pages.
As with everything you work on, repairing today’s vehicles is getting more difficult, so it is important to use all the tools you can to make your task easier. Mode 6 is simply another tool in the toolbox. Until next time, remember, “The more you take care of your car, the more it takes care of you”.
