Modern vehicles are marvels of engineering, packed with sophisticated control units – about ten times more than cars from the 1990s. This technological leap means diagnosing car troubles can often be as simple as reading error codes. This is where On-Board Diagnostics (OBD2) scanners become indispensable tools for car owners.
Learning how to use an OBD2 scanner can save you significant time and money on car repairs. This guide provides everything a typical driver needs to understand about these handy devices.
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What is an OBD2 Scanner and Why You Need One?
An OBD2 scanner is a powerful diagnostic tool that connects to a special port in your car to gather data from its various control units. This data includes diagnostic trouble codes (DTCs), also known as fault codes, and real-time information, often called live data. Live data encompasses readings from various sensors throughout your vehicle, such as pressure, temperature, and speed.
Alt text: Car mechanic using an OBD2 scanner for computer diagnostics to read fault codes.
This information originates from numerous sensors embedded within the car’s systems. Fault codes typically appear when a sensor reading falls outside of the normal operating range or if a sensor stops responding altogether. When your car’s computer detects an issue, it stores a fault code and often illuminates the “check engine light” on your dashboard.
More advanced OBD2 diagnostic tools offer additional functionalities beyond reading fault codes. These can include performing service resets, activating service functions needed for tasks like brake pad replacement, and even module coding, which is necessary when replacing certain electronic components in modern vehicles.
On-board diagnostic systems became a standard feature for all cars manufactured in the United States from 1996 onwards and in Europe from 2004. This standardization ensures compatibility across different makes and models, making OBD2 scanners universally useful.
Types of OBD2 Scanners: Choosing the Right Tool
The market offers a wide variety of OBD2 scanners to suit different needs and budgets.
The most affordable and basic option is a Bluetooth OBD2 code reader. These compact devices pair with your smartphone via Bluetooth and, when used with a compatible app, can read fault codes and display basic live data. Typically costing just a few dollars, Bluetooth OBD2 readers are a convenient entry point for the average driver wanting to understand their car’s basic health.
For car owners who are more inclined towards DIY car repairs, a more capable standalone OBD2 scanner is a worthwhile investment. These devices, often priced starting around $100 and upwards, not only read fault codes and live data but also offer features like resetting service lights, initiating service procedures for tasks like replacing brake pads, and accessing more in-depth live data parameters.
Professional mechanics and automotive technicians often require even more advanced tools. Standard OBD2 scanners may fall short when dealing with the complexities of modern vehicle systems and the diverse range of issues they encounter, from routine oil changes to complex engine repairs. Professional-grade OBD2 diagnostic tools offer extensive capabilities beyond basic fault code and live data retrieval.
With specialized software and hardware, professional OBD2 tools can perform advanced coding and programming functions. This level of access allows experienced technicians to adjust virtually every configurable option within a modern car’s electronic systems. However, these professional tools can cost thousands of dollars and are generally too complex for the average car owner to operate effectively.
How to Read OBD2 Fault Codes: A Step-by-Step Guide
Reading fault codes is the foundational step in OBD2 diagnostics. If you intend to use an OBD2 scanner, learning this process is crucial. While the specific controls and menu layouts may differ slightly between various scanner models, the underlying principle remains consistent.
Here’s a step-by-step guide on How To Scan Obd2 fault codes:
1. Locate and Connect the Scanner
All modern cars are equipped with a standardized OBD2 port. This port is typically located beneath the steering wheel, often in the driver’s side footwell area, or sometimes in the center console. The OBD2 port is often concealed by a small plastic cover, so you may need to look carefully to find it. Once located, plug your OBD2 scanner firmly into the port.
Alt text: Diagram showing the typical location of an OBD2 scanner port under the steering wheel in a car.
Many newer OBD2 scanners and code readers utilize Bluetooth connectivity instead of physical wires. If you are using a Bluetooth scanner, ensure it is properly paired with your smartphone or other device according to the manufacturer’s instructions.
2. Turn On the Ignition (Accessory Mode)
Computer diagnostics via OBD2 require the car’s electrical system to be active, so you must turn the ignition on before initiating a scan. The “ignition on” position, also known as accessory mode, provides power to the car’s electrical systems without starting the engine. To minimize electrical load during the scan, it’s advisable to turn off unnecessary accessories like headlights, the radio, and the air conditioning.
While some vehicles allow fault code scanning with the engine running, accessory mode is generally sufficient and preferable for initial diagnostics. Fault codes are stored in the car’s computer memory and will persist until they are intentionally cleared. Starting the engine might be necessary when you want to observe live data readings under different engine conditions.
3. Identify Your Vehicle
Once the OBD2 scanner is connected and the ignition is on, the next step is to identify your specific vehicle to the scanner. This typically involves selecting your car’s make, model, and year from the scanner’s menu. This information is essential for the tool to correctly recognize your car’s control units and accurately interpret the data readings.
Many modern diagnostic tools are equipped with an automatic vehicle identification system. This feature can automatically detect your car’s VIN (Vehicle Identification Number) and use it to automatically configure the necessary vehicle information. If the automatic VIN recognition fails for any reason, you can also manually enter the VIN into the scanner.
4. Initiate the Fault Code Scan
With the vehicle information entered, you can now proceed to initiate the fault code scan. Locate the fault code reading or diagnostic scan option in your OBD2 scanner’s menu. Most scanners offer options to scan specific control units individually or to perform a comprehensive scan of all available control units in the vehicle.
If you are unsure about navigating the scanner’s menus, consult the integrated help section within the tool or refer to the user manual provided by the scanner manufacturer. These resources should provide clear guidance on how to initiate and perform a fault code scan on your specific device.
The duration of a full system scan can vary depending on the car model and the number of control units it has, typically ranging from a few seconds to several minutes.
5. Analyze the Fault Codes
After the scan is complete, the OBD2 scanner will display any stored fault codes. These fault codes are the key indicators that trigger warning lights on your instrument cluster, such as the check engine light, ABS light, or airbag light.
Sometimes, fault codes are relatively straightforward and descriptive. For example, a code like “C0031- Right Front Wheel Speed Sensor Circuit” clearly points to a potential issue with the right front wheel speed sensor or its circuit. In such cases, the fault code provides a strong indication of the faulty component.
However, it’s important to understand that fault codes often indicate a symptom or a system malfunction, not necessarily the direct cause of the problem. For instance, a common fault code “P0171 – System Too Lean (Bank 1)” indicates that the engine’s air-fuel mixture is too lean. While the code signals a lean mixture, the underlying cause could be various factors, such as a clogged fuel filter, a failing fuel pump, a vacuum leak in the intake system, faulty oxygen sensors, or issues with other engine management components.
Pro Tip: Utilizing Live Data for Deeper Diagnostics
Beyond reading fault codes, the ability to access and interpret live data is a valuable asset for diagnosing complex car problems. Most OBD2 scanners provide a live data or real-time data section, allowing you to monitor various sensor readings and system parameters as the car is running.
How can live data assist in troubleshooting? Consider a scenario where your car is experiencing a noticeable power loss, and the only fault code present is a generic “limp mode” notification. In this situation, live data can be incredibly helpful. By monitoring parameters such as fuel pressure, boost pressure (for turbocharged engines), intake airflow, and intake manifold pressure, you can assess whether these readings are within their normal operating ranges. Deviations from expected values can pinpoint the source of the issue.
Alt text: Close-up of an OBD2 scanner displaying live data readings during a car diagnostic process.
However, even with access to fault codes and live data, diagnosing car problems can sometimes be challenging. Interpreting the data, understanding complex fault code descriptions, and pinpointing the root cause often requires automotive knowledge and diagnostic experience. In complex cases, seeking professional help from a qualified mechanic is advisable.
OBD2 Scanners: An Essential Tool for Used Car Inspections
The used car market can present potential pitfalls for buyers. Dishonest sellers may attempt to conceal vehicles with hidden issues, ranging from mechanical problems and electrical faults to undisclosed accident history or even legal encumbrances.
While obtaining a vehicle history report is a crucial step in used car due diligence, a thorough pre-purchase vehicle inspection is equally vital to avoid unexpected and costly repairs down the line.
Before purchasing any used vehicle, it’s highly recommended to always obtain a vehicle history report and perform an OBD2 scan to check for stored fault codes. If you don’t own an OBD2 scanner or are unsure how to use one effectively, it’s wise to take the car to a trusted mechanic for a professional pre-purchase inspection. A mechanic can perform a comprehensive check, including an OBD2 scan, to identify potential issues before you commit to the purchase.
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Clearing OBD2 Fault Codes: Proceed with Caution
Scanning for fault codes is a diagnostic step to identify potential issues. Fault codes themselves rarely reveal the direct cause of a problem. Even when an OBD2 scan indicates a faulty mass airflow sensor, experienced mechanics will typically use a multimeter to test the sensor and its wiring to confirm the fault before replacing any parts. Surprisingly often, fault codes can be triggered by issues like damaged wiring, loose electrical connections, or corrosion rather than a faulty sensor itself.
After addressing the identified problem and performing the necessary repairs, it’s essential to re-scan the car for fault codes. If the original fault code no longer appears after the repair, it suggests the issue has been successfully resolved, and you can confidently get back on the road.
However, simply clearing fault codes without addressing the underlying problem is not recommended. While clearing codes will turn off the check engine light and other warning lights, the underlying issue will likely persist, and the fault codes may reappear soon. Furthermore, clearing codes indiscriminately can erase valuable diagnostic information that could be helpful for future troubleshooting.
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Article by
Evaldas Zabitis
Evaldas has been writing since middle school and has had a passion for cars for as long as he can remember. Right after getting his driver’s license, he spent all of his savings on shoddy cars so he could spend time fixing, driving, and selling them. Evaldas is always interested in automotive technical innovations and is an active participant in automotive community discussions.
