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OBD codes Explained: Learning how to interpret OBD codes

OBD codes Explained

OBD II codes are essential in diagnosing car issues. With the right tools, anyone can read and possibly interpret them correctly. Read on for more on reading OBD II Codes. Some people know these codes as Diagnostic trouble Codes DTC or OBD II codes. There are several hundred codes that belong to 4 popular groups.

While you don’t need to know all of them, there are some popular codes that are worth learning as a vehicle owner. OBD II codes are specific to OBD II compliant vehicles like light trucks, SUVs and the likes. These codes are based on the onboard diagnostics system that generates a code whenever a problem is detected. This unique code is helpful to interpret and understand the nature of the problem. Read on for more on reading OBD II codes.

How to Read OBD II codes – A quick guide to OBD II codes

OBD is short for on board diagnostics. It forms part of the self-diagnosis OBD II code system that help monitor various parts of your vehicle. These include the control module, body, engine and the works. The codes generated typically start with a letter indicative of the part of the vehicle at fault. Before we can breakdown the codes and teach you how to read them, it is important you learn how to insert your code reader.

Inserting and reading an OBD scanner

In order to read these codes, you need a proper reading device or scan tool. Because the connectors on all OBD compatible models are the same, you do not need to worry about a special adapter. The software required to read these codes however may vary. You will therefore need to a tool equipped with software compatible to year, make and model of your car. Here is a quick guide to properly inserting your scanning device;

First locate the 16-pin Diagnostic Link Connector usually underneath the dash close to the steering column. Not all the connectors are located here; some models have the connector on the center console or elsewhere.

Next, you will plug in your scanning device and turn on the ignition without staring the engine. This way, you are able to connect the code reader to the vehicles computer.

Lastly, push the read codes button or select read codes option depending on the device model you are using.

The scanning tool will run a diagnostic and present you with the diagnostic fault codes in numerical order. Take a record of these codes for reference. Your device might not display the meaning of the codes, which may require you to look up the definitions somewhere else.

Interpreting the result

If you are unfamiliar with OBD II codes, you might not be able to recognize the issue right away. You don’t need to know all the codes and what they mean, but there are some popular diagnostic codes vehicle owners should familiarize themselves with. Before you can learn the different codes, you may want to acquaint yourself with how these codes are structured in the first place. This will make learning the codes and making a self diagnosis way easier.

As we mentioned, codes are generated with a starting code that denotes the art of the vehicle with an issue. Here are the OBD categories and what they represent.

  • U Network and vehicle integration which includes the functions managed and shared by the onboard computer systems.
  • P Power train that includes the engine, transmission and other associated accessories.
  • C Chassis which includes the mechanical systems and functions
  • B Body that includes the parts found in the passage compartment zone

A number to complete the code follows these letters. The number is either 1 or 0. Zero if the code is a generic or standardized one and 1 if it manufacturer specific.

The third character identifies a particular vehicle system. These run from 0 to 7 making them eight systems in total. The fourth and fifth characters complete the DTC. The two digits run between 0 to 99 and help identify the exact issue you are dealing with.

The two types of OBD II Codes

Apart from the category system of OBD II codes, there are two types of DTC that apply to OBD II codes: type 1 and type 2. Type 1 codes are more immediate issues that are associated with quick and severe damage. Type 2 are not as important and can wait, however, they must be dealt with eventually. The presentation of codes in either group varies depending on what type they are. Type 1 codes for example are presented in a single freeze frame after one driving cycle fails while types two codes will set a pending trouble code after a single failed driving cycle, and then store a freeze frame after two consecutive failed cycles.

Codes for check engine light

Formally, the check engine light is known and the Malfunction Indicator Lamp MIL and it will inform you when there is an issue with your engine. Depending on the manufacturer, the light can be yellow, amber or orange and even red. This engine light may sometimes start flashing, indicative of a much serious problem. While there are some common codes that are worth knowing, it is difficult to describe all check engine lights.

TIP: Some manufacturers have color coded the indicating light, orange for a common issue and red for a more serious one.

The PD after an engine code

You might be familiar with OBD II codes but once in a while soothing might surprise you. The PD after your engine codes for example, is indicative of pending DTC. The intermittent code will prompt the system to store the pending code that hasn’t matured to trigger the engine check light. Some codes require a consecutive series of faults to show up; hence they are stored ad pending issues.

Permanent Trouble codes – what they are and what they mean

Permanent codes can be a pain especially when you don’t understand how to handle them, or why they are there. OBD II or DTC are codes that notify you of an issue with your vehicle. There are multiple types of codes that can be generated depending on the nature of your problem. Each code has its own unique 5 digits, with each constituent digit carrying significant information regarding the nature of the problem. Using the second digit, which is either 1 or 0, you may establish whether the code is manufacturer specific or generic. If you are interested in permanent codes, then understanding this difference should be useful to start you off on learning about permanent codes. Read on for more on permanent codes.

What is a permanent code?

These are a type of generic/standard codes. As we mentioned, OBD II codes have a special arrangement that allows you to determine whether they are generic or manufacturer codes. The second character of the code will help you establish this. Zero is the notation given for standardized codes. P0XXX for instance is a generic code while P1XXX is a manufacturer code.

Pending codes, confirmed codes and permanent codes form art of the generic group of codes. Pending codes indicate that a system in the vehicle is behaving strangely and will not turn on your check engine light. Confirmed codes on the other hand are indicative of one of the systems experiencing issues that require your attention. Confirmed codes will turn on any indicators to alert you of the faulty system.

Lastly permanent codes are those that cannot be cleared from the scanning tool. They only go away once the vehicle is checked, repaired and enough data of normal functioning of the system is recorded by your computerized car management systems. Permanent codes are relatively new compared to pending and confirmed codes. They are emission related and are useful when it comes to emission related inspections.

Clearing a OBD II Permanent Fault Code

Unlike other codes, PDTCs cannot be cleared by standard means like disconnecting the battery or erasing the scanning tool. They are intended to ensure that a vehicle does not pass in use inspection even if the codes are cleared or erased prior. You can only clear these codes in one of two ways.

First is running three consecutive error or issue free monitoring cycles. The check engine light will turn off and the Permanent trouble codes will be cleared after a fourth fault free monitoring run. Alternatively, you could run a confirmed error free monitoring cycle and follow it up with a clear codes request on your scanning tool. These drive patters affirm to the computer that the fault has been repaired and the vehicle can now continue to run safely.

What does a successful monitoring / driving cycle entail?

  • The total time since the engine starts running must be more than ten minutes
  • The vehicle must operate for above 25 miles per hour for more than five minutes
  • Your vehicle must continuously be idle i.e. operate at under one mile per hour for more than thirty seconds
  • Your OBD monitor must run and establish that the fault is no longer present.

TIP: you might detect a PDTC without the check engine coming on. This only means that the system is yet to verify the permanent code.

Permanent Trouble Codes and emissions

PDTCs have evolved over the years and can now be used to make emissions testing easier. As we mentioned, you can’t just clear these codes by conventional means. This will stop any dishonest individuals from clearing the codes prior to inspection. Once the computer systems know that the issue has been handled for sure, then the PDCTS will go away.

What happens when you clear ODB codes on your car?

Learning about OBD II codes is essential for the welfare of your vehicle. As a car owner, must know everything from reading the codes, interpreting the most common ones and clearing them when necessary. OBD II codes are helpful especially for pinpointing where the issue is. Knowing how to read and interpret them is only a part of these codes. Additional knowledge in resetting your Check engine light, clearing the codes and checking if they have been cleared will help further your know how on these codes. Take a look at clearing OBD II codes for more insight.

Ways you can clear OBD II codes

Before you clear the codes, you must hook up a scanner to the vehicle so you can read the automated diagnosis. Here are some ways you can reset your check engine light.

With an OBD II Scanner

Vehicles made since 1996 have standard OBD II systems that use a computer system to detect errors throughout the car and generate codes to indicate where the fault has occurred. You can read these codes with a scanning tool that attaches to the 16 pin diagnostic port, usually found below the dash. After you successfully hook on the device, turn on the scanner and then turn on the car. The device will check for any codes generated by the system once you press the read button. Do not attempt to clear codes without first handling the maintenance issues that the codes have raised. Next press erase on the scanner and your check engine light will turn off as the codes are cleared.

TIP: Because of all the different brands and models of scanning tools, the layout or button instructions may vary from tool to tool.

In case you do not own a scanning tool, you may ask the people at your service center to reset the check engine light with their code readers. Again, they will want the faults addressed before clearing them and the best option is to comply. If you only want a reset, ask them kindly to reset the service engine soon light and if it turns on again, you will visit for a diagnosis.

Disconnect the battery

This is an easy way to reset the check engine light without a scanner, this old school method is ideal for some car sad n might not work that well with some vehicles. First, remove the positive and negative terminals and then drain any available electricity the battery, you can do this by honking for a minute or 30 seconds.

TIP: If the check engine light is still on after removing and reconnecting the battery, then you might need to see a mechanic for more professional advice.

Word of caution on battery disconnection

Disconnecting the battery in attempt to clear OBD II codes might also reset some other settings like the radio, clock or memory settings. Some newer models have a sleep mode that allows you to disconnect the battery without interfering with other settings; you should check your manual for details on this feature.

Clearing Permanent DTCs

Unlike the other codes, you cannot erase permanent fault codes by these means. There is a specific driving pattern that you must follow in order for the computer to recognize that the fault has been repaired and the codes can then be cleared. The module strategy involved in clearing Permanent Diagnostic Trouble Codes is strict and must follow the instructions provided by the driving pattern in order to successfully complete a driving cycle and register it as successful for the system to detect.

TP: Permanent codes are emissions related and therefore stop anyone trying to pass their emission inspection from erasing them. This way, the system forces you to keep your vehicle at acceptable pollution levels.

Driving with the Check Engine Light on: What are the risks?

Pulling over because the Check Engine Light came on can be quite bothersome, especially if the situation doesn’t count as an emergency. That blinking yellow or red light is something every driver is familiar with. Most of the times when the Check Engine Light comes on, you just want to ignore it. It isn’t such a big deal right? Wrong! Sometimes, ignoring the Check Engine Light is safe, however, there are instances when the issue is serious enough to warrant stopping.

What does Check Engine Light mean?

The Check Engine Light is a malfunction indicator that is generated from your vehicles computerized engine management system. It tells you if there is something wrong with the emissions system. Any change or faulty functioning of the components or sensors triggers the light which is displayed on the dashboard. Just because the check engine comes on does not mean you go into frenzy and start to panic. There are instances when the light is harmless, such as when you turn on your car, the Check Engine Light comes on. It should turn off after 6 seconds if nothing is unusual with the components or sensors.

Telling the Check Engine Lights apart

While the color of this indicator does not change, the light can either be steady or blinking. When the light is steady, your vehicle has a minor fault, but when flashing, it means that there is a severe fault with your car. There are different engine or emissions issues that trigger the light all of which vary in severity.

TIP: For a more specific diagnostic, you can read the OBD II code/ readings with a special code reader or scanning tool. The code generated will pin point the exact issue with your vehicle.

How many miles can you drive safely with the check engine light on

As I said, the nature of the Check Engine Light should guide your next steps. When the light comes on and it is FLASHING, you may want to take the risk. Because flashing is indicative of immediate cause for alarm, you should consider getting your vehicle checked out as soon as possible. The mechanics could run a diagnostic checkup and help solve the issue as quickly as they can. Alternatively, you could run a self-diagnosis and visit a professional for further insight.

Once you establish the urgency of the situation, try and reduce your speed. Try and avoid erratic surges and take it easy on the engine. Lastly, you might want to check your gas cap. If the light comes on after refueling, it might be that the cap isn’t tightly placed. Once the cap is tightly corked, then the light should be reset.

Driving with the check engine light on all depends on the severity of the situation. Yes, you can drive with your check engine light on but the question is should you? Your decision should be based on the collective information you gather from observing how your vehicle is functioning even with the light on. As long as the vehicle isn’t performing strangely, driving with the light on shouldn’t be a big problem. However, you will still need to run a diagnosis and determine what exactly could be the cause.


Reading and interpreting OBD II codes is an important part of diagnostics. Without this computerized system, identifying the issue with your vehicle might be difficult even for professionals let alone self-diagnosis. You may want to know common codes and what they mean just in case your engine light starts blinking in the middle of the road. This way, you can gauge the severity of the issue and determine when it is best to go for a checkup.


Where can I have my check engine light?

When this light comes on it is a source of concern to many people. What many know is that it can relate to minor issues like not closing your gas pump to serious engine problems. When this light turns on, go slow on the gas pedal and stop by the roadside. First, check the gas cap, then open your bonnet and check the condition of your engine. You can have the real cause for the “check engine light” diagnosed at the nearest auto shop or use a scan tool to self-diagnose yourself.

Can I purchase an OBD scanner?

The tool is available for purchase by anyone. Cars have undergone lots of changes since the 1990s and most today come with onboard computers. The On-Board diagnostic scanner is a tool that enables you to understand what your car’s engine error codes really mean. The codes will start been illuminated whenever the check engine light comes on. In the engine computer system you will have a microprocessor that in real time reads all the inputs from the various engine sensors. If the readings are not optimal it will send Diagnostic trouble codes.

How much does an OBD scanner cost?

Unlike in the past today we have a wide variety of OBD scanner tools each equipped with a wide variety of reading options. The cost can range anywhere from $30 to over $1000. The cheaper versions will only read some selected information while the more expensive ones are more detailed and ideal for highly computerized cars. If you are not sure about the model to get for your car, talk to your mechanic for assistance. Most of them have interacted with a wide variety of ODB scanner tools in the market. Ensure that the buttons used are not complex and the screen is wide enough to display the error codes.

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Steven Reilly is a qualified mechanic and his passion for cars goes beyond just the technical aspects. He is also an amateur racer and all round car enthusiast. When he is not driving them, he can often be found in his garage under the hood of a rare model. Steven Reilly has lost track of the number of hours he has spent setting up his fine collection of rebuilt models. He believes that cars can provide a constructive and fun opportunity to teach the youth important life skills. In line with this, he is developing a community outreach program, potentially dubbed ‘Cars for change'.



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