Global OBD-II Diagnostics: Massive Amount of Data Available

Feb. 11, 2022

There is plenty of proof that 80% of the top 10 emission diagnostic trouble codes (DTCs) can be solved by diagnosing the data from the global side of a scan tool. In addition, many other issues can be diagnosed using the 10 modes from the global side of a scan tool. I know of shops, mine included, when a customer comes in for a standard oil change we plug it into the diagnostic link connector (DLC) and utilize the global side of the scan tool to check for DTCs or pending DTCs.

Over the years, there has been a lot of debate over brands of aftermarket scan tools as to which brand is best and which brand has the most coverage. In addition, there have been some credible arguments as to the value of the original equipment manufacturer (OEM) scan tools. I know that most of us technicians spend the bulk of our time on the enhanced side of an aftermarket scan tool. In this article, our objective is to create some awareness of the diagnostic value from the massive amount of diagnostic information available from the 10 modes from the global side of a scan tool. (See Fig. 1). I call this side of the scan tool the plug-and-play side whereas no VIN is required. If your scan tool is behind on several updates, you can still access the global side of the scan tool on a 2021 model year vehicle.

Mode 1

Mode 1 gives us all the important powertrain data. All of this data is raw data meaning that no substituted values will be displayed. In the event of a sensor or circuit failure, the failed value will be displayed. On the enhanced side of a scan tool, you could be looking at a substituted sensor or circuit failure value. Take a look at Fig. 2 screen 1 from Mode 1. This data is from a 2012 Chevy Equinox. Notice that we are pointing out the commanded equivalent ratio. This data represents the corrected air-fuel ratio the engine is presently under. Numbers below .9 mean the engine has been running too rich and the powertrain control module (PCM) is correcting.

Numbers above 1.10 mean the engine is running too lean and the PCM is correcting. Ideally, this value should be between .9 and 1.10.  Lean codes are among the top 10 DTCs on mass airflow-equipped (MAF) vehicles. Most technicians know that a faulty MAF sensor could be the cause. Other causes could be low fuel pressure, a vacuum leak, restricted injectors or E-85 fuel in a non-E-85 engine. Take a look at Fig. 3  from Mode 1. Notice the MAF reading captured at idle on a 3.0L engine. The grams per second at idle should be slightly higher than the liter size of the engine. You can also monitor the MAF grams per second at wide-open throttle (WOT) and at 5,000 RPM. You would simply multiply the liter size of the engine times 40 on engines equipped with fixed valve timing. On engines such as this 3.0L with variable valve timing, multiply the liter size of the engine times 50. This engine should pull a minimum 150 grams per second at WOT and 5,000 RPM. This rule applies to altitudes below 1,000 feet above sea level. If the freeze-frame conditions show that the lean code was captured during idle and low load conditions, we may strongly suspect a false air or vacuum leak. Lean conditions across all engine RPMs and load conditions lead to suspected E-85 fuel in a non-flex-fuel vehicle. Under road load conditions, as RPMs increase and fuel trim values increase, we would strongly suspect a faulty MAF sensor.

This is where Mode 2 freeze-frame data can be very helpful. Restricted converters and retarded valve timing issues also will have a major effect on the engine’s ability to breathe. Monitoring the MAP value under engine-loaded conditions would also be necessary. Retarded valve timing issues and restricted converters will cause the fuel trim values to go into double-digit negative values under loaded conditions. If you are working on an Asian or European vehicle, where the MAF values are not indicated in grams per second, then simply use the calculated load parameter. A minimum calculated load of 80% would be needed at WOT conditions and 5,000 RPM. All of these parameters are available in Mode 1. While we are looking at the data in Mode 1 Fig. 3 notice the barometric pressure (Baro) and manifold absolute pressure (MAP) readings. Baro minus the MAP values equals the engine vacuum. In this case, the manifold vacuum is 16.5 inches. In addition, notice the short-term and long-term fuel trim values combined together represent the total fuel trim values. In this example, the total fuel trim values are minus 3.9%. Total fuel trim values should be within plus or minus 10% of the number 1. One disadvantage of Mode 1 is that the data speed is much slower than that of the enhanced side of the scan tool. This does not minimize the importance of the reliable raw data available from the global side of the scan tool in Mode 1. Take a look at more Mode 1 data in Fig. 4. Notice on this gasoline direct injection (GDI) vehicle, the low side fuel pressure value is displayed at 56.1 PSI. In addition, the O2 voltages are displayed as well as an 18% duty cycle command to the purge solenoid. With this purge on time, we should see a vacuum in the evaporative emission control (EVAP) system by monitoring the EVAP pressure sensor, which is also available from the Mode 1 data. In Fig. 5, including Mode 1 data, we can see the high side fuel rail pressure on this GDI engine at 587.2 PSI captured during idle, no-load conditions.

At WOT condition, you should see this value will exceed 2,000 PSI. If you recall, from Fig.4 that the duty cycle to the purge solenoid was 18%, then we should be building a vacuum in the EVAP system. This is indicated in Fig. 5 with the EVAP pressure sensor indicating 100 kPa (Kilopascal). Another important parameter is the distance since the malfunction indicator lamp (MIL) has been requested. This tells us how many miles the car owner has driven with the MIL on. This can be critical in the event of a misfire code where raw fuel can build up in the converter and light off and destroy the converter. Keep in mind that in cases of a misfire the PCM will suspend the catalyst monitor. After fixing the misfire, we would not initially clear the MIL. A short test drive will allow the PCM to run the catalyst monitor. We could then go to the Mode 6 menu and view the catalyst monitor test results to see if the converter survived the misfire. Most modern-day systems will disable the injector from a misfiring cylinder to prevent damage to the converter.     

Mode 2

Mode 2 contains the freeze-frame data in the event of a MIL and a DTC. It is always advisable to spend some time here and analyze what the conditions were when the PCM set the code and requested the MIL (conditions such as temperature, engine load, vehicle speed, time since startup, throttle angle and engine RPM). There are usually a lot of clues here that can help us in our diagnostics. Take a look at an example of a freeze-frame from a P0302 DTC in Fig. 6 from a 2010 Toyota Prius. Are there any clues that would be helpful in diagnosis? Notice that the misfire occurred 40 seconds after startup with an engine load of 54%. The engine temperature was barely warm at 77 degrees with the engine RPM at 1,492. It is very likely the engine is in closed-loop condition. These would be the conditions we would most likely have to duplicate. Since we have this information we strongly suspected an air-fuel ratio problem causing the misfire. The number 2 coil easily fired an ST125 spark tester. Compression values from the number 2 cylinder were within a normal range. With the injectors on the flow bench, we found three of the four injectors with excessive flow rates causing a rich condition. This resulted in the PCM to lean out all four injectors, causing a lean density misfire on the number 2 cylinder. 

Mode 3

Mode 3 displays the current emission trouble codes. Remember the majority of the top 10 emission DTCs require two consecutive failures before the PCM requests the MIL.

Mode 4

Mode 4 clears all emission DTCs. When using this function, remember that the code or codes will be cleared along with the valuable freeze-frame data, which will also be lost. More importantly, the test results from the once per trip monitors we will cover in the Mode 6 area of this article will also be cleared and the status from all of the once per trip monitors will go back to incomplete. This means that a specific long comprehensive drive cycle must be completed to reset all of the once-per-trip monitors to complete status and update the Mode 6 test results. Many technicians do not initially clear the code. After the repair is made a test drive is conducted to allow the specific monitor related to the DTC to run. You can then analyze the specific monitor test results to verify a good fix.

This works for most of the top 10 emission trouble codes except for the EVAP monitor. In many cases, it takes a six-hour cold soak, which is part of the enable criteria that must be met be before the EVAP monitor runs. Technicians in emission test areas are known to leave the MIL on. In most cases with two to three good drive cycles with no repeat failures, the PCM will turn off the light and dump the code. The reason here is that the once-per-trip monitors will indicate complete rather than incomplete. If the vehicle owner needs to go into an emission test, if the once per trip monitors indicated incomplete, the car will fail the emission test. Keep in mind that some DTCs will cause the PCM to suspend some monitors. For example, in cases of a misfire code, the PCM will suspend the catalyst monitor. After the misfire problem is corrected and the MIL is not cleared, a test drive can be done to allow the catalyst monitor to run to ensure the converter survived the misfire problem by viewing the Mode 6 test results from the catalyst monitor.

Mode 5

Mode 5 was originally designed to indicate the once-per-trip monitor’s test results from the O2 sensors and O2 heating circuits. However, most scan tools incorporate these O2 sensor test results into the Mode 6 section, which is what we will do in this article.

Mode 6

Mode 6 information includes the valuable test results from the last time a once-per-trip monitor ran. Take a look at all of the possible once per trip monitors in Fig. 7. No vehicles will have every one of these once-per-trip monitors as they will vary depending on the year, make and model. Mode 6 test results can be used to determine which component failed to set the code and also be used to confirm a good fix. Early Ford systems, for example, have as many as six Mode 6 test results just from their early exhaust gas recirculation (EGR) system, which covers all of the components of the EGR system. The information you will see here from Mode 6 data is phenomenal and very comprehensive. Many technicians will initially scan the test results briefly to simply note a pass-or-fail status of the once-per-trip monitors. Because of the massive amount of information available from Mode 6, we will need to do a condensed coverage in this article in that we will cover a few of the many Mode 6 test results. Beginning in model-year 2010, Mode 6 also contains individual cylinder misfires from the last 10 drive cycles. See Fig. 8. This data has proven very valuable, especially on the GDI engines that have a reputation of a misfire during a cold startup from restricted injectors or leaking injectors. The misfire usually goes away after a few seconds. I have found in these cases that the Mode 6 info usually points out the misfiring cylinder. 

Some early onboard computer (OBD-II) systems did not disable the injector from the misfiring cylinder. On these systems, raw fuel will end up in the converter and light off, creating extreme converter temperatures, which crystallize the converter substrate. When the PCM detected the cylinder misfire, the converter monitor was suspended. After the misfire problem was corrected from a faulty injector, we simply left the MIL on and took the vehicle for a test drive, allowing the B1 converter once-per-trip monitor to run and to update. Notice the B1 converter monitor test results in Fig. 9, indicating a pass with good test results. The test results indicate a .969 while the minimum value test result indicates a .350 and the maximum value is 8.00. These values represent the switching ratio between the front and rear O2 sensors. This is how the PCM determines the O2 storage capacity and the use of the O2 molecules to burn off the HC and CO. You may have had a customer request that you check out a used car for them before they decide to buy it. Once the under car components are checked out and the underhood inspection is done, spend some time analyzing the Mode 6 test results.

Let’s say this vehicle is a relatively high mileage vehicle. Noting the Mode 6 test result from the once-per-trip catalyst monitor let’s assume the max test result is 7.034. This is very close to the maximum limit of 8.00. We then could inform the customer that the converter is losing its efficiency and the PCM is very close to setting a converter code. The catalyst monitor also will be suspended in the event of an upstream or downstream O2 failure. Let’s say the MIL is on with an upstream or downstream O2 code. We now have replaced the faulty O2 sensor with a known good brand. We did not clear the MIL. A short startup is needed for the O2 heater monitor to run and the monitor for the O2 switching times. Take a look at the Mode 6 test results after a faulty O2 sensor was replaced in Fig. 10. The Mode 6 test results from the rich-to-lean and lean-to-rich switching test results show a pass. In addition, note the minimum and maximum values. Notice that the switching time test result for a rich-to-lean indicated 22 milliseconds while the test results for a lean-to-rich transition indicate a good value of 13 milliseconds. Not all manufacturers display these values in milliseconds as in this General Motors (GM) system. The strategy here is that if the test results are very close to the minimum or maximum values on any of the once-per-trip monitors, it could mean a predictable failure. Let’s examine the O2 heater monitor test results after the O2 sensor was replaced. Notice the O2 sensor heater monitor test results in Fig. 11. Notice an initial pass with a test result of 0. Notice the max value of 8. We now know that the B1 S1 sensor was online very quickly.

Valve timing issues on engines equipped with variable valve timing codes can be caused by a number of issues such as sludge buildup in the oil, low oil pressure, a loose timing chain, a faulty cam actuator, or a faulty control solenoid or its circuit. A vehicle came in with a cam position code on Bank 1. The oil level was two quarts low, and sludge buildup was evident. The control solenoid was removed only to find more sludge buildup. An ohmmeter test indicated a good value of 10.9 ohms resistance. We informed the car owner we could try an oil change followed by an engine flush and replace the control solenoid. Please note that no guarantee was expressed to the car owner. The word try comes into place here.

There are times when we simply have to make a judgment call and that needs to be communicated to the car owner, much like a medical doctor writes a prescription to his patient and informs him to report back as to whether or not there were any improvements to his symptoms. Let’s look at the Mode 6 test results from the variable valve timing (VVT) monitor from Bank 1 after the control solenoid was replaced and the engine flush and oil change completed in Fig. 12. Initially notice that the monitor passed. The test results show a 0. The minimum value is 0, and the max value is 100. The scale being used is not fully understood, but the 0 appears to indicate no cam variance.

One of the most popular Mode 6 test results covers the EVAP system. A generic P0440 code is a general EVAP failure that could include a large leak, lack of purge or a vent solenoid stuck in the open position. Let’s look at the purge monitor test results from Mode 6 in Fig. 13. Did you notice the initial pass? This tells us that purge is working and the issue would likely be a large leak. In addition, remember you have individual Mode 6 test results for a .020 small leak and a .090 large leak. Keep in mind, there are many other Mode 6 test results we didn’t have the space to cover in this article. You can easily see these by spending some time on the global side of the scan tool.

When Ford initially came out with the Mode 6 test results back in the mid-90s, the scan tool indicated a TID (test identification) number in a hexadecimal format, and it did not specifically identify what monitor it was applying. Also, the term (CID) was used to mean “component ID.” In addition, we had to use some very complex conversion formulas to arrive at some understandable value. This is one of the reasons why a lot of technicians were confused with this data. For example, on early Ford systems, Mode 6 gave individual cylinder misfire data. You would need to multiply the test results times .000015 to obtain an individual cylinder misfire value on a percentage scale. With the advent of controller area network (CAN) compliant systems, the two terms now used are MID (monitor id) and TID (test id). Now each individual monitor is identified in English terms. 

Mode 7

Mode 7 contains the pending or pending codes. Most of the top 10 emission DTCs are two trio codes, meaning that the PCM must see two consecutive failures before lighting the MIL and setting a code. A single failure will set a pending code along with freeze-frame data. Even when a car comes into your shop with an issue with no MIL, we should access this mode and look for a pending code. What could happen is once you have worked on the car and say, two days later, the pending code has finally matured and the PCM lights the MIL. We all know what customers think is that you worked on the vehicle two days ago and now they have a MIL. The customer’s normal approach to us is that we must have done something wrong. Have you been there before?

 In addition, Mode 7 will display the status of the continuous monitors. Unlike the once-per-trip monitors, these monitors run continuously. The continuous monitors include the misfire monitor, the air-fuel ratio monitor and the comprehensive component monitor. The codes from these monitors are usually one-trip failure codes with a MIL.

Mode 8

Mode 8 is what I refer to as the worthless mode. It sometimes is called the output control monitor. On some vehicles and some scan tools, it will command the vent solenoid to close during key on, engine off (KOEO) conditions so that we can seal the EVAP system while smoke pressurizes the system. Most of us technicians opt for the enhanced side of the scan tool for this procedure.

Mode 9

Mode 9 displays the VIN and the present PCM calibration. In my opinion, it is much easier to read the VIN from the scan tool in Mode 9 rather than looking thru the windshield. This mode is where we go to find the last PCM calibration number before we go online to see if a later calibration is needed to correct a variety of possible issues. See Fig. 14.

Mode 10

Mode 10 contains the permanent DTCs. Codes displayed here are permanent DTCs that consistently fail on every key cycle. Some refer to these codes as “hard codes.” These codes are usually caused by a component failure or a circuit failure.

Many of us technicians will do a complete bus circuit sweep test to confirm whether or not any module on the network has reported a trouble code. This procedure is available from the enhanced side of the scan tool. If a module has reported a DTC, we should always make a note of it on the work order.

The objective of this article is to bring some awareness to the vast amount of information available from the global side of the scan tool. Good technicians are more than just code readers. Access all of the information from the global side of the scan tool in your journey down the diagnostic road. This industry is better because of your commitment. 

About the Author

Bill Fulton

Bill Fulton is the author of Mitchell 1's Advanced Engine Performance Diagnostics and Advanced Engine Diagnostics manuals. He is also the author of several lab scope and drivability manuals such as Ford, Toyota, GM and Chrysler OBD I and OBD II systems, fuel system testing, many other training manuals in addition to his own 101 Lab Scope Testing Tips. He is a certified Master Technician with over 30 years of training and R&D experience. He was rated a Top Technical Trainer and has instructed for Mitchell 1, Precision Tune, OTC, O'Reilly Auto Parts, BWD, JD Byrider, Snap-on Vetronix and Standard Ignition programs. You may have also seen Fulton in many Lightning Bolt Training videos and DVDs and read his articles in many auto service magazines. He currently owns and operates Ohio Automotive Technology, which is an automotive repair and research development center.