Mode Six Onboard Test Results is the OBD-II service that reports the detailed outcomes of the self-tests your engine computer runs on emissions systems. Instead of a simple pass or fail, it shows the measured test value alongside the minimum and maximum limits the computer used to judge it.
For a DIYer, this service can reveal a system that is close to failing before a trouble code sets, or confirm that a repair actually brought a test result back within its limits. It is also one of the least understood scan-tool functions, so this guide explains what it contains and how to read it carefully.
The Report Card Behind the Check Engine Light
Your engine computer, the powertrain control module (PCM), constantly tests its own emissions systems. These tests are called monitors. Some run continuously, such as misfire detection, while others run only under specific conditions, such as the catalyst, evaporative emissions, and oxygen sensor monitors.
When a monitor finishes, the computer compares the result with its limits. If the result falls outside them, a pending code may set, and repeated failures can turn on the check engine light. Most scan-tool screens only show this final outcome as codes and readiness status.
Mode 06 shows the details underneath. It reports the actual numbers the monitor produced and the limits it used. Think of it as seeing the score on each exam rather than only whether the student passed the course. That extra detail is what makes Mode 06 so useful.
How Mode 06 Results Are Organized
Mode 06 data is grouped by the monitor that produced it. Within each group, individual tests have their own identifiers. The way these identifiers work depends partly on the vehicle’s communication protocol, which affects how easy the data is to read.
Monitor and Test Identifiers
On vehicles using ISO 15765, the CAN protocol required on US vehicles from model year 2008, results are organized by monitor identifiers, often called MIDs, and test identifiers, called TIDs. The standard defines how many of these are scaled and which units they use.
A capable scan tool translates these identifiers into names, such as a catalyst monitor test for bank 1, and shows the values in readable units.
Older Pre-CAN Vehicles
On earlier vehicles using SAE J1850, ISO 9141-2, or ISO 14230 (KWP2000), Mode 06 results were often reported with test and component identifiers whose meaning and scaling were defined by the manufacturer.
For these vehicles, the raw numbers may be difficult to interpret without the manufacturer’s documentation. Some scan tools show unlabeled values, which should not be interpreted by guesswork.
Test Value, Minimum, and Maximum
Each test result typically includes three numbers: the measured test value, a minimum limit, and a maximum limit. If the value falls between the limits, the test passed; if it falls outside them, it failed.
Some tests use only one limit, with the other shown as a default value. The tool may also display a pass or fail label to make reading easier.
Monitors Commonly Reported in Mode 06
The monitors available in Mode 06 depend on the vehicle and engine, but several appear frequently on gasoline vehicles. Knowing them helps you find the right test when a code or concern points to a particular system.
- Catalyst monitor results for each bank, related to codes such as P0420.
- Oxygen sensor and sensor heater tests, including response and switching behavior.
- Evaporative emissions (EVAP) leak tests, related to codes such as P0442.
- EGR system tests on vehicles equipped with exhaust gas recirculation.
- Misfire data by cylinder on many CAN vehicles.
Diesel vehicles report different monitors, such as those for particulate filters and other aftertreatment systems. Interpretation for those systems is more complex and is best left to the service manual and qualified technicians.
Reading a Result Step by Step
A Mode 06 screen can look intimidating, but a consistent routine makes it manageable. Work through one monitor at a time and focus only on the tests related to your concern.
Start by identifying the monitor, such as the catalyst monitor for bank 1. Then look at the test value and its limits. Ask two questions: did it pass, and how close is it to the limit? A value well inside the limits means little concern; a value right at the edge deserves attention.
Check the units and the direction of the limit. For some tests, a higher number is worse; for others, a lower number is worse. The position of the limits tells you which way failure lies. If the tool does not label the units or test name clearly, do not guess at the meaning.
Finding Problems Before a Code Sets
One of the most practical uses of Mode 06 is spotting a marginal system. A monitor can pass while producing a result close to its limit. No code sets, yet the system may be on its way to failing, and the next cold morning or long drive could push it over.
This is common with misfire data on vehicles that report per-cylinder misfire counts. A cylinder that shows occasional misfires in Mode 06, while others show none, may be developing a problem long before the misfire monitor sets P0301 or a similar code.
Treat these findings as early warnings, not diagnoses. A marginal result points you toward a system to inspect and test. It does not prove a component has failed, and replacing parts based on a near-limit value alone often wastes money.
Using Mode 06 With Codes and Live Data
Mode 06 works best alongside other OBD-II services. Each one provides a different kind of evidence, and together they give a more complete picture than any single screen.
- Read stored, pending, and permanent codes to see which monitors reported a problem.
- Review the freeze frame to understand the conditions when the fault was recorded.
- Check Mode 06 for the related monitor to see how far the result was from its limit.
- Watch live data from Mode 01 to observe the system under similar conditions.
For example, with a pending P0420, Mode 06 can show how far the catalyst test value was from its limit, and live data can show the upstream and downstream oxygen sensor behavior. That combination guides your next tests, such as checking for exhaust leaks or misfires.
Confirming a Repair With Test Results
Mode 06 is also valuable after a repair. Once the monitor runs again, its new result shows whether the repair actually moved the test value safely within its limits, rather than only proving that no code has returned yet.
Remember that clearing codes resets the monitors and their results. After clearing, the monitors must run again before fresh Mode 06 data appears. The conditions each monitor needs, such as temperature, speed, and fuel level, vary by manufacturer and are described in the service information.
Comparing before-and-after results is a strong way to verify your work. If a catalyst result moved from the edge of its limit to comfortably inside it after an exhaust leak repair, you have good evidence the repair addressed the cause.
Common Misreadings to Avoid
Mode 06 is precise, which makes misreading it easy. The most common error is assuming every value can be compared with a universal number. Test values and limits are specific to the vehicle, engine, and calibration, so a result from one car cannot be judged against another car’s limits.
Another mistake is reading tests that have not run. If a monitor has not completed since codes were cleared, its Mode 06 entries may show default or zero values. Check readiness status in Mode 01 before trusting any result.
A third mistake is interpreting unlabeled or manufacturer-defined values on older vehicles. Without correct scaling and definitions, the numbers can be completely misleading. When the tool cannot identify a test clearly, rely on the service manual or a technician rather than an assumption.
Scan Tool Support for Mode 06
Not every code reader displays Mode 06. Basic readers often focus on codes, freeze frame, and readiness. Mid-range generic scan tools usually include Mode 06 screens, though the quality of their labels and unit conversion varies.
A good Mode 06 display names each monitor and test, shows values with units, and marks results as pass or fail. If your tool only shows raw hexadecimal numbers, it can still communicate with the vehicle, but you will need documentation to make sense of the data.
Before relying on Mode 06 for an important decision, test your tool on a vehicle you know is healthy. Seeing what normal results look like on your own car helps you recognize unusual values later and confirms that your tool presents the data in a readable way.
Making Monitor Results Work for You
Add a Mode 06 check to your routine whenever a code appears or a monitor seems slow to complete. Save the results with the date, mileage, and the conditions of recent driving, so you can compare them over time and spot a system that is gradually weakening.
Use the results to decide what to test next, then follow the manufacturer’s diagnostic procedure for the related system. Inspect wiring, check for leaks, and confirm the component’s operation before replacing anything. Mode 06 tells you where to look, not which part to buy.
For diesel aftertreatment, hybrid systems, or results you cannot interpret confidently, bring your saved data to a qualified technician. Clear records of Mode 06 results help them confirm the issue quickly, and they give you a meaningful way to check the repair afterward.