Using OBD2 Mode $06 for advanced car diagnostics

What is Mode $06?

Mode $06 is an advanced diagnostic functionality mode included as part of the On-Board Diagnostic standard (OBD2). It keeps track on how emission control components and other systems and sensors are functioning. Mode $06 allows access to the results for on-board diagnostic monitoring tests of these systems. These systems or components can be either continuously monitored (e.g. misfire monitoring) or non-continuously monitored (e.g. catalyst system). Continuous monitors run all the time while the non-continuous monitors run only after certain conditions are met.

OBD2 Mode $06 is sometimes referred just as Mode 6. The Mode 6 reveals the actual self-test data that is used by the OBDII system to detect faults and readiness monitor results. It enables more complete analysis of the DTCs and readiness monitor test results.

Mode $06 monitors

Here’s a list of the On-Board Diagnostic Monitors defined by the OBD2 standard at the moment. OBD Auto Doctor supports them all.

  • 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

In addition to these standard defined monitors, manufacturers can have proprietary monitors. Our software can access the manufacturer specific Mode $06 data but it won’t be able to give the monitors or tests a name. It will give you the Monitor ID (OBDMID) and the Test ID (TID) and the data values. You will have to look up the meaning of those from the service manuals, or you can search the Internet for more help. For example, if you have GM vehicle, check out the OBD Mode $06 definitions for GM cars.

How can Mode 6 help?

The Mode 6 data can help you in many ways depending on your level of expertise and experience with cars. OBD Auto Doctor will give you the result and limit numbers plus the test result (pass/fail). The numbers can reveal a lot of the inner workings of the car if you are able to give the them a more detailed meaning in the correct context. The data can help you for example in the following ways:

  1. You can detect emerging problems before they set an active error code.
  2. You can find issues that are causing runnability problems, but that have not developed into active errors yet.
  3. You can use the data to identify whether a Diagnostic Trouble Code was set by a major failure or if the test just barely failed.
  4. You can verify that the repairs made have actually fixed the correct problem. You don’t need to wait for days for certain OBDII self-tests to run and possibly turn the Check Engine Light on.

Mode 6 data can reduce a lot of guesswork by eliminating components and systems out of the problem. But to get the most out of the data, you need to have a bit of knowledge of how the engine works.

Example: Engine Misfires

Many technicians find the misfire checking the most useful part of the Mode $06. Every time a cylinder misfires, the system increases the misfire counter for that cylinder. Only if the misfire count exceeds a certain threshold, it will result in a misfire trouble code. If the misfire count stays below the limit, no trouble code is set and no notice is provided for you. But you might be still able to feel the misfire when the engine is under heavy load or acceleration.


OBD2 Mode 06 misfire data
Example of OBD Auto Doctor reading OBD2 Mode $06 misfire data. Click to open larger image!


With the help of the OBD Auto Doctor, you can read the actual misfire counts recorded for each cylinder. The purpose of the misfire data is to help you identify which cylinders are currently misfiring and identify which cylinders have been consistently misfiring in previous driving cycles. Typically the misfire count should be equal or close to zero. In this case, there’s no problem. If a single cylinder misfire count is relatively higher compared to the other cylinder misfire counts, it indicates a possible issue. It tells that the cylinder is experiencing an abnormal behavior, and that there’s a problem with the ignition, fuel or compression in that cylinder. Remember that misfire counts for cylinder should only be compared relative to each other.

Final words

In this article, I explained the basics of the OBD2 Mode $06 also known as the On-Board Diagnostic Monitors. I hope the text gave you clear introduction to these monitors and how then can be used for car diagnostics. To get started analyzing your car, download the OBD Auto Doctor software for a PC or Mac now!

Please note that not all On-Board Diagnostic Monitor IDs or Test IDs are supported by all systems. The software is able to show only the monitors and tests that the car provides. Moreover, some older cars might not even support the Mode $06 at all. Use the free version of the software to see what data your car provides. Even the free version will list the available monitors and tests.



OBD Readiness Monitors Explained

Once in a while we get questions about OBD Readiness Monitors. This post will explain what the readiness monitors are.

The purpose of readiness monitors in a car is to self-test the car’s emission systems. Readiness monitors are self check routines that observe the performance of specific vehicle emissions control systems. Cars may perform up to 11 system tests; these are so called readiness monitors. The output of readiness monitors identify whether the car’s computer has completed the required tests while the car is being driven.

Readiness Monitor types

There are two different types of monitors: continuous and non-continuous. Continuous monitors are different in design from the non-continuous monitors. Continuous monitors are being constantly tested and evaluated by the car’s computer while the car is running. Conversely, the non-continuous monitors require certain conditions to be met before a test or series of tests can be completed. The conditions necessary for the car to run these self-diagnostic tests vary. Some monitors require that the car follows a predefined “drive cycle” routine. Some require two drive cycles due to the need for a cool down and warm up periods in between.

Continuous Monitors

  • Misfire
  • Fuel System
  • Comprehensive Component


Continuous readiness monitors read with the Windows Phone app
Continuous readiness monitors read with the Windows Phone app


Non-Continuous Monitors

Non-continuous monitors are different for spark ignition cars (gasoline engines) and compression ignition cars (diesel engines).


Spark ignition vehicles (Gas)
  • Catalyst (CAT)
  • Heated Catalyst
  • Evaporative (EVAP) System
  • Secondary Air System
  • Oxygen (O2) Sensor
  • Oxygen Sensor Heater
  • EGR (Exhaust Gas Recirculation) and/or VVT System
Compression ignition vehicles (Diesel)
  • NMHC Catalyst
  • NOx/SCR Aftertreatment
  • Boost Pressure
  • Exhaust Gas Sensor
  • PM Filter
  • EGR and/or VVT System


Non-continuous readiness monitors read with the Android app
Non-continuous readiness monitors read with the Android app


Monitor status

Each readiness monitor will have it’s own output status. The completion status can be:

  • Ready or complete (green mark) meaning that the test has been completed e.g. the OBD-II system has checked this emissions control system.
  • Not ready (red mark) meaning the test is uncompleted e.g. the OBD-II system has not checked this emissions control system.

OBD Auto Doctor reports the status only for supported monitors in the mobile apps. The desktop version (Windows, Mac, Linux) lists the unsupported monitors too. They are marked as unsupported. It simply means that the car doesn’t have that monitor and therefore it can’t be tested.


OBD readiness monitors read with the Mac version
OBD readiness monitors read with the Mac version


Monitor “not ready”

Clearing the diagnostic trouble codes (DTCs) will reset the monitor statuses. This typically occurs during vehicle repair. Statuses are reset in case of power failure too. This usually happens when the battery has been disconnected. Therefore it is not advisable to disconnect the battery. If you need to disconnect the battery for example to replace it, read further to learn how to get the monitors back to complete.

Note! Depending on your country and state, OBDII vehicle may not pass the annual inspection unless the required monitors are “ready”. For example, the US Environmental Protection Agency guidelines allow up to two monitors to be in a “not ready” state for model year 1996 through 2000 vehicles and one monitor “not read” for 2001 and newer model year vehicles.

How to get the monitors “ready”?

  1. First, make sure that the MIL (Malfunction Indicator Light) is not commanded on. Having stored or even pending diagnostic trouble codes active may prevent a monitor from running to completion.

  2. Second, make sure that you have enough fuel in the car. Some monitors, for instance the EVAP monitor, may require the fuel level to be between 35% and 85% to initiate the diagnostic testing.

  3. Third, complete the so called “drive cycle”. About one week of combined city and highway driving is usually enough to allow the monitors to reach complete status. The drive cycle is explained in more details in the next paragraph.

OBD drive cycle

The purpose of the OBD2 drive cycle is to let your car run on-board diagnostics. This, in turn, allows monitors to operate and detect potential malfunctions of your cars’s emission system. The correct drive cycle for your car can vary greatly depending on the car model and manufacturer. Also, the monitor in question affects the required drive cycle.

Today, many vehicle manufacturers include these drive cycles in the vehicle owner’s manual. Typically, a few days of normal driving, both city and highway, will make the monitors ready. The following generic drive cycle can be used as a guideline if a specific drive cycle is not known. It will assist with resetting monitors when a car specific drive cycle is not available. However, it may not work for all cars and monitors.

The drive cycle can be difficult to follow exactly under normal driving conditions. Therefore, it is better to drive it in restricted area!

  1. The universal OBD-II drive cycle begins with a cold start (coolant temperature below 50 C /122 F, and the coolant and air temperature sensors within 11 degrees of one another). This condition is easily achieved by letting the car to sit overnight.

  2. The ignition key must not be left on prior to the cold start. Otherwise the heated oxygen sensor diagnostic may not run.

  3. Start the engine and idle the engine in drive for two and half minutes, with the A/C and rear defroster on if equipped.

  4. Turn the A/C and rear defroster off, and accelerate to 90 km/h (55 mph) under moderate, constant acceleration. Hold at a steady speed for three minutes.

  5. Decelerate (const down) to 30 km/h (20 mph) without braking or depressing the clutch for manual transmissions.

  6. Accelerate back to 90-100 km/h (55-60 mph) at 3/4 throttle. Hold at a steady speed for five minutes.

  7. Decelerate (const down) to a stop without braking.

Get ready for inspection

To avoid being rejected in the annual inspection, you can prepare your car for it yourself. Do not wait until the annual inspection with your issues. If the check engine light comes on, read the diagnostic trouble codes and engine status immediately. It could save you a lot of time as well as future repair and fuel costs. You can do all this with OBD Auto Doctor diagnostic software. You can read all the monitors statuses even with the free version. Try the software now!



How OBDII helps you when buying a used car

Purchasing a used car can be a tedious process. The chances that you make a good deal might not be so good. However, if you succeed in it, you can save a lot of money and trouble. Read more about how OBD Auto Doctor assists you to achieve this goal.

But how can you make such good a deal, how can you be sure that the car has real mileage and was properly maintained, for example? Even more, some of the problems can be hidden, such as engine and transmission problems. These hidden problems might not have come out during the test drive. The key to closing the deal successfully is to eliminate these potential problems beforehand.

Reveal the Hidden Problems

First of all, one of the most beneficial means to making a good deal on buying a used car is to reveal the hidden problems immediately. OBD Auto Doctor is the tool for accomplishing this task. With our software, you can verify that the Check Engine Light (Malfunction Indicator Lamp, MIL) is really turned off, thus revealing a broken light bulb, for example. You can also check that the Diagnostic Trouble Codes (DTCs) were not incorrectly previously turned off without fixing the real problems that caused the issues. The OBD2 software also reports the pending DTCs with a click of a button. A pending DTC is a diagnostic trouble code that is stored permanently only if the fault occurs a certain number of times. A pending DTC indicates a future issue and you should take them seriously when buying a used car. The pending trouble code will remain pending until the fault condition occurs the required number of times. In this case, the DTC will be then stored permanently. A permanent diagnostic problem will light up the MIL and requires you to fix the issue as soon as possible. On the other hand, if the malfunction does not re-occur during a set period of time, the pending DTC will be automatically cleared.

Some interesting OBD parameters when examining a car:

  • Distance traveled while MIL is activated
  • Number of warm-ups since DTCs cleared
  • Distance traveled since DTCs cleared
  • Engine run time while MIL is activated
  • Engine run time since DTCs cleared

Note that the actual list of available parameters is vehicle specific and not every car supports every parameter.

Check the VIN

Secondly, you should absolutely check the car’s history records before proceeding any further. You can do this easily even on-line with Vehicle Identification Number (VIN). The VIN is a helpful identifier in this case, since a VIN is a unique for every car and it specifies the fingerprint of the vehicle. Typically, the VIN can be found by looking at the dashboard near windshield on the driver’s side of the vehicle (refer the car’s user manual for the specific location). You can also fetch the VIN with OBD Auto Doctor, and verify that the car engine has the same VIN as the physical tag. By comparing the physical VIN and the VIN reported by the OBD2 software, you can tell for sure that the car has the right engine in it.



What to do when Malfunction Indicator Light illuminates?

Check Engine Light

It is not unusual for people to get interested in On-Board Diagnostic when the Malfunction Indicator Light (MIL) lights up on the dashboard of their vehicles. The purpose of the Malfunction Indicator Light, which is also known as Check Engine Light, is to indicate a detected problem with the vehicle’s engine, transmission or emission control system and alert the driver about the issue. The OBD system illuminates the light only for a reason and it should not be ignored; the cause should always be investigated.

The Check Engine Light indicator can signal three different types of problems.

  • Occasional flashes indicate temporary engine malfunctions. In this case, it is good to be aware of the possible forthcoming issues which can later on turn to more serious ones.
  • The most common case is when the indicator light stays on constantly. It indicates more serious problem that requires action to be taken; the sooner the better. Although, sometimes the issues aren’t that serious but can affect the emissions of the vehicle, for example.
  • The most serious type of signaling is when the MIL flashes constantly. It is a sign that your vehicle’s engine is seriously misfiring. The issue is major and the engine should be stopped immediately to prevent serious damage. For instance, the condition might cause the catalytic converter to overheat and even cause a fire.

N.B. It is totally normal for the light to illuminate for a few seconds when a vehicle is first started and extinguish when the engine is running.

Some OBD-II issues are relatively small and don’t really have much impact on engine operation. On the other hand, some of the issues are major and require appropriate measures to be taken. Unfortunately, there is no way to distinguish between them by just looking the MIL. The only way to find out what’s wrong with the vehicle is to plug in a OBD2 scan tool and read the Diagnostic Trouble Code(s) from the system. Every time the OBD system illuminates the MIL light, it will also store a Diagnostic Trouble Code (DTC) in the engine control unit of the vehicle to give information about the detected issue.

It is possible for the OBD system to turn the MIL off automatically if the conditions for the problem cease to exist. After evaluating a system or component under test for three consecutive times without detecting the problem, the light can be extinguished. However, usually the light remains ON. If you happen to own a OBD-II scantool (for example one with ELM327 chip) and a OBD diagnostic software, you can check the reason for the problem yourself immediately. For example, OBD Auto Doctor gives you the DTC code and description that guides you towards the main cause of the problem. With diagnostic software, you can even reset the MIL yourself after fixing the problem. It is important to clear the Check Engine Light because, for example, a vehicle will fail emission testing if the MIL light is ON when being tested.

Below is a screen shot of OBD Auto Doctor diagnostic tool for OBD systems. From the image, you can see how the DTC, system and textual description of a trouble code are illustrated. You’ll also see the button for clearing the trouble codes and the MIL.


Diagnostic Trouble Codes Illustrated


Scantool Garage Open

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