Lesson 1: What to do when Check Engine Light illuminates.
Hi, great to see you again! Let”s make sure you know what to do when the check engine light illuminates.
People usually get interested in the On-Board Diagnostics when the Check Engine Light illuminates on the dashboard of their car. The Check Engine Light is also known as the Malfunction Indicator Light (MIL). The purpose of this warning light is to indicate a detected problem with the car and alert you about the issue.
The OBD2 system illuminates the light when there is a problem with the car’s engine, transmission or emission control system. The light turns on only for a reason and you should not ignore it. You should always investigate the cause.
What does the Check Engine Light mean?
The light 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. Yet, 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 all the time. It is a sign that your vehicle’s engine is misfiring. The issue is a major one and you should stop the engine immediately to prevent serious damage. For instance, it 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 you start the engine. But it should go out when the engine is running.
How to get more information about the issue?
Some of the OBD-II issues are relatively small. Those don’t have much impact on engine operation. On the other hand, some of the issues are major and need appropriate measures to be taken. Unfortunately, there is no way to distinguish between them by just looking at the MIL.
The only way to find out what’s wrong with the car is to use on-board diagnostic tool. The tool and accompanied software can read the Diagnostic Trouble Code(s) from the system. Every time the OBD system turns on the MIL light, it will also store a Diagnostic Trouble Code (DTC) in the electronic control unit. The DTC will give information about the detected issue.
What are the next steps?
If you have an OBD-II adapter already and OBD diagnostic software installed, you can check the reason for the problem yourself. For example, OBD Auto Doctor can read the DTC code from the car and give you description of the code. Those will guide you towards the main cause of the problem.
With diagnostic software, you can even reset the MIL yourself. It is important to clear the Malfunction Indicator Light after fixing the problem. This is because, for example, the car will fail emissions testing if the MIL light is ON when tested.
Now that you know what you should do when the light comes up, in the next email I will show you how to read the diagnostic trouble codes and reset the check engine light.
OBD Auto Doctor
OBD Auto Doctor
Lesson 2: How to read trouble codes and reset the Check Engine Light (CEL)
In Lesson 1 you learned that the Check Engine Light indicates that there is a problem with the car. Either the engine is having a problem or the emission control system has detected an issue. This malfunction is indicated by triggering the Check Engine Light (CEL).
This warning light is the main indicator to warn you about problems with the vehicle. Ignoring the warning can cause serious damage to the car.
There is always at least one OBD2 diagnostic trouble code associated with the check engine light. When the vehicle detects an issue, it will set an active trouble code and trigger the light. Today I will show you how to read the diagnostic trouble codes and reset the Check Engine Light yourself.
Read the Diagnostic Trouble Codes
Reading the diagnostic trouble codes (DTCs) is an important step to start with. The DTCs will tell you the reason for the fault. The codes help you identify the issue and determine the cause.
Reading the codes is easy.
- Prepare the vehicle for connection by turning ignition key to the ON position. Don’t start the engine because to reset the light, the engine shouldn’t be running.
- Launch the OBD Auto Doctor software and connect to the dongle.
- To read the DTCs with the desktop software, navigate to Trouble Codes from the left navigation panel. The software will read and show the information.
- Change the tab in the top to switch the view between confirmed, pending and permanent DTCs and freeze frame.
Reset the Check Engine Light
Most of the time the diagnostic trouble codes appear for a good reason. You should investigate the codes and fix the issues causing the errors. Only after fixing, you should proceed to resetting the check engine light. If you haven’t fixed the issues, the same codes might come back immediately.
However, sometimes the error codes occur from a random failure and there’s nothing to fix. In this case, you can reset the check engine light and hope the issue doesn’t come back. If it wasn’t just a random failure, the error returns. Yet, you should ensure that there are no problems with the car every time before doing the reset.
Resetting the check engine light will clear the diagnostic trouble codes too. It will also clear all other diagnostic information such as stored freeze frame data and status of test results. After the reset, the car may run poorly while it performs re-calibration.
One important thing to note is that resetting the CEL will reset the readiness monitors. This means that your car will not pass emissions inspection immediately after the reset. Because the emissions data is deleted, the smog device will fail your car. We will cover the readiness monitors the day after tomorrow.
After you have read the DTCs, you can continue to clearing the codes and the warning light. To reset the Check Engine Light with your computer:
- Click the Clear the DTCs button in the Trouble Codes view. Read and acknowledge the information presented.
Now, the reset command is send to the car and the light is cleared.
Resetting the Check Engine Light is a very easy process. More work is required for analysing the root cause of the warning and fixing the possible issues. Luckily, the car itself helps you to get started. It provides the Diagnostic Trouble Codes and other diagnostic information about the problem.
You can avoid expensive dealer visits by reading the codes and resetting the warning light yourself. It’s a good idea to get the software and dongle right now. Waiting for the actual issues to appear might be too late. Getting yourself familiar with the tools when everything is working fine is a great start.
Tip: Avoid battery reset
Resetting the DTCs is sometimes also possible by disconnecting the battery for awhile. We do not recommend this method. New vehicles can have systems that need constant battery voltage. Disconnecting the battery can cause new issues with these systems. For example, the car theft system or infotainment system might be reset. Resetting the DTCs with a OBD tool is the recommend way. That’s how the professional mechanics do it and you should too.
In the next leasson, Lesson 3 I will explain you the formula of the diagnostic trouble codes.
See you then,
OBD Auto Doctor
Lesson 3: Diagnostic Trouble Codes explained:
We have learnt how to read the diagnostic trouble codes in Lesson and reset the check engine light in Lesson 2. I will now explain the format of the trouble codes in more details.
Diagnostic Trouble Codes or OBD2 Trouble Codes are codes that the car’s OBD system uses to notify you about an issue. Each code corresponds to a fault detected in the car. When the vehicle detects an issue, it will activate the corresponding trouble code.
A vehicle stores the trouble code in it’s memory when it detects a component or system that’s not operating within acceptable limits. The code will help you to identify and fix the issue within the car.
Each trouble code consists of one letter and four digits, such as P1234. This lesson will teach you how to interpret the meaning of the codes.
Format of the OBD2 Trouble Codes
System or Category
The OBD2 Trouble Codes are categorised into four different systems.
- Body (B-codes) category covers functions that are, generally, inside of the passenger compartment. These functions provide the driver with assistance, comfort, convenience, and safety.
- Chassis (C-codes) category covers functions that are, generally, outside of the passenger compartment. These functions typically include mechanical systems such as brakes, steering and suspension.
- Powertrain (P-codes) category covers functions that include engine, transmission and associated drivetrain accessories.
- Network & Vehicle Integration (U-codes) category covers functions that are shared among computers and systems on the vehicle.
The first letter of the code will mark the system related to the trouble code.
Generic and manufacturer specific codes
The first digit in the code will tell you if the code is a generic or manufacturer specific code.
Codes starting with 0 as the first digit are generic or global codes. It means that they are adopted by all cars that follow the OBD2 standard. These codes are common enough across most manufacturers so that a common code and fault message could be assigned.
Codes starting with 1 as the first digit are manufacturer specific or enhanced codes. It means that these codes are unique to a specific car make or model. These fault codes will not be used generally by a majority of the manufacturers.
The first digit might be also 2 or 3. In this case the type depends on the system. B2xxx and C2xxx codes are manufacturer controlled while B3xxx and C3xxx codes are reserved at the moment. P2xxx codes are generic codes while P3xxx codes are manufacturer controlled. U2xxx codes are manufacturer controller as well as U3xxx codes.
Subsystem or functional area
Previously, the second digit defined the sub-system of the codes. However, the latest document defining the diagnostic trouble codes (J2012 revised in 2016-12) had some changes to this.
According to the document, as the DTC usage has increased with the introduction of new technology to vehicle systems, it was necessary to remove the grouping of DTCs into functional areas.
The last two or nowadays three digits define the actual fault description. These numbers will tell the particular problem and each code is defined separately. There’s no formula to decode these codes automatically.
Luckily, OBD Auto Doctor software contains the fault description for over 18 000 diagnostic trouble codes. There’s no need to memorize the format of the codes because you can read them with the car diagnostic software.
Next is Lesson 4. We will learn about readiness or emissions monitors.
Until next time!
OBD Auto Doctor
=========Lesson 4 next==========
Lesson 4: What are OBD2 Readiness Monitors?
Welcome back to the next section of our on-board diagnostics email course!
In the previous Lessons you learnt about diagnostic trouble codes and the check engine light. Now, we continue to other aspects of on-board diagnostics. Today I will explain you what the OBD2 readiness monitors are.
OBD2 Readiness Monitors are simple yet powerful self check routines. They provide insight to the car’s self-diagnostics.
The purpose of readiness monitors is to self-test the car’s emission control systems. The monitors are also known as Emissions Monitors. Like the name indicates, they observe the performance of car’s emission related systems.
Cars may perform up to 11 system tests or routines. These tests are so called readiness monitors. The output of readiness monitors tell you whether the car’s computer has completed the tests successfully.
Readiness Monitor types
There are two different types of readiness monitors: continuous and non-continuous. Continuous monitors are different in design from the non-continuous ones. Continuous monitors are being constantly tested and evaluated while the engine is running. The non-continuous monitors need certain conditions to be met before a test can be completed.
The conditions necessary to run the non-continuous self-diagnostic tests vary. Some monitors require that the car follows a predefined drive cycle routine. Some require two drive cycles because of the need for a cool down and warm up periods between. Each emission monitor can have different requirements for the conditions.
Previously, the OBD2 standard (SAE J1979) categorised each defined monitor as either one. In the latest standard edition, this definite allocation is no longer present for all of them. Thus, OBD Auto Doctor doesn’t follow the categorization anymore either.
Continuous or Non-continuous Monitors
These monitors can be of either type. It’s up to the manufacturer to decide.
- Fuel System
- Comprehensive Component
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
Traditionally, the only monitor status was the status since the diagnostic trouble codes were cleared. This readiness monitor status is mandatory for all OBD2 compliant vehicles. It will show the long term status after the check engine light was reset and the DTCs cleared.
As the OBD2 has evolved, newer vehicles can now report emission monitor status also for the current driving cycle. These monitors start from the beginning every time when the monitoring cycle begins. Older cars might not support this feature. In that case, OBD Auto Doctor will mark it as NA or Not Available.
Readiness monitor test result yields the monitor status. Each readiness monitor will have its own output status. The completion status can be:
- Complete or ready meaning that the test has been completed. It means that the OBD-II system has checked this emissions control system and it has passed the test. OBD Auto Doctor indicates this by green check mark.
- Incomplete or not ready meaning the test is not completed. It means that the OBD2 system has not been able to run this routine or it has failed. OBD Auto Doctor indicates this by red exclamation mark.
- Disabled meaning that the test has been disabled for the rest of this monitoring cycle. A monitor can be disabled when there is no easy way for the driver to operate the vehicle to allow the monitor to run. For example, the ambient air temperature might be too low or too high.
OBD Auto Doctor lists all the defined monitors in the software. But the actual status can be reported only for the ones that the car supports too. It is not required for a car to support all the monitors. NA or not available monitor means that the car doesn’t have that monitor. Thus it can’t be tested.
Why is a monitor incomplete or “not ready”
Clearing the diagnostic trouble codes (DTCs) and the Check Engine Light will reset the monitor statuses too. This typically occurs during or after vehicle repair.
Statuses are also reset in case of power failure. This usually happens when the battery has been disconnected. That’s why it is not advisable to disconnect the battery.
For the current monitoring cycle, or “this drive cycle”, the status is set to incomplete upon starting a new monitoring cycle. It is a normal situation for these monitors to be incomplete when starting the engine.
Get ready for inspection
Depending on your country and state, OBDII vehicle may not pass the annual inspection unless the required monitors since reset are complete. For example, the US Environmental Protection Agency guidelines allow up to two monitors to be not ready for model year 1996 through 2000 vehicles. For 2001 and newer model year vehicles only single monitor status can be incomplete or not ready.
To avoid rejection in the annual inspection, you can prepare your car for the check yourself. You should at least read the readiness monitors and make sure they are ready. This will save you from almost guaranteed rejection.
You can do all this with free version of OBD Auto Doctor diagnostic software.
And remember, do not wait until the annual inspection with the issues. Acting immediately could save you a lot of time as well as future repair and fuel costs.
That was a lot to go through. Let’s take some rest. We’ll continue the series tomorrow by learning OBD Mode $06 for more advanced diagnostic.
OBD Auto Doctor