Modern vehicles are significantly more complex than cars from the 1990s, boasting ten times more control units. This sophistication means a greater capacity for self-diagnosis, accessible through error codes. This is where On-Board Diagnostics (OBD2) scanners become invaluable tools for car owners.
Learning how to use an OBD2 scanner can save you considerable time and money on car repairs. Here’s a comprehensive guide for the average driver to understand and utilize these devices effectively.
What is an OBD2 Scanner and What Does it Do?
An OBD2 scanner is a diagnostic tool that connects to your car’s OBD2 port, allowing it to communicate with the vehicle’s computer system and retrieve data from its control units. This data includes diagnostic trouble codes (DTCs), also known as fault codes, and real-time information, such as sensor readings for pressure, temperature, and speed.
Alt text: A mechanic uses an OBD2 scanner connected to a car to perform computer diagnostics.
This information originates from various sensors throughout your vehicle. Fault codes typically appear when a sensor reading falls outside of the normal operating range or if a sensor becomes unresponsive. Think of it as your car telling you, “Hey, something isn’t quite right here!”.
More advanced OBD2 diagnostic scanners offer additional functionalities beyond reading codes. They can perform service resets, activate specific service procedures like retracting brake calipers for pad replacement, and provide more in-depth live data streams. Some even offer coding capabilities necessary when replacing electronic components in newer cars.
Since 1996 in the United States and 2004 in Europe, OBD2 compliance has been mandatory for all new cars, making these diagnostic systems a universal feature in modern vehicles.
Understanding the Types of OBD2 Scanners
The market offers a wide array of OBD2 scanners, each with varying capabilities and price points to suit different needs.
For the budget-conscious and those needing basic diagnostics, a Bluetooth OBD2 code reader is an excellent entry-level option. These affordable devices pair with your smartphone via Bluetooth and, when used with a compatible app, can read fault codes and display basic live data. They are user-friendly and perfect for quick checks and understanding the ‘check engine light’ warnings.
If you’re a DIY enthusiast planning to undertake more involved car maintenance, investing in a more feature-rich OBD2 scanner is advisable. These scanners, often priced starting around $100, can reset service lights, perform service functions like electronic parking brake release, and access a broader range of live data parameters. These are often handheld devices with their own displays and interfaces, offering more independence and functionality than basic Bluetooth readers.
Professional automotive technicians require the most sophisticated tools. While standard OBD2 scanners are helpful, they lack the advanced capabilities needed for complex repairs and programming. Professional-grade OBD2 diagnostic tools provide extensive features like module coding, component programming, and in-depth system analysis. These powerful tools can cost thousands of dollars and require specialized training to operate effectively, making them suitable for professional workshops.
Step-by-Step Guide: How to Read OBD2 Fault Codes
Reading fault codes is the foundational skill for anyone using an OBD2 scanner. If you want to diagnose car problems yourself, this is the essential first step to learn.
While the specific controls and menus may differ slightly between OBD2 scanner models, the general process for reading codes remains consistent.
1. Locate and Connect the OBD2 Scanner
Every modern car equipped with OBD2 has a designated OBD2 port. This port is typically located beneath the steering wheel column or within the center console area. It’s often hidden by a small plastic cover, so you might need to look closely to find it. Once located, plug your OBD2 scanner firmly into the port.
Alt text: Diagram showing the typical location of an OBD2 port under the steering wheel in a car.
Many newer scanners and code readers utilize Bluetooth for wireless connectivity. If you’re using a Bluetooth scanner, ensure it is properly paired with your smartphone or chosen device according to the manufacturer’s instructions.
2. Turn on the Ignition
OBD2 diagnostics require the car’s ignition to be turned on to power up the computer systems. Before initiating a scan, turn the ignition to the “ON” position. This is typically the position just before you would start the engine. To minimize battery drain, it’s advisable to turn off unnecessary electrical loads like headlights, radio, and air conditioning.
While some vehicles allow fault code scanning with the engine running, keeping the ignition on is generally sufficient for retrieving stored fault codes. Starting the engine becomes more relevant when you want to observe live data readings in real-time. Remember, fault codes are stored in the car’s computer memory and will not disappear until they are intentionally cleared, regardless of whether the engine is running.
3. Vehicle Selection
Once the OBD2 scanner is connected and the ignition is on, the next step is to identify your vehicle to the scanner. This allows the tool to correctly interpret the data from your car’s specific control units and sensors. You will generally need to input the make, model, and year of your vehicle.
Most modern diagnostic tools are equipped with an automatic VIN recognition system. This feature automatically detects your car’s Vehicle Identification Number (VIN) and uses it to retrieve the necessary vehicle specifications. This streamlines the setup process and ensures accurate communication with the vehicle’s systems. If automatic VIN recognition fails, you can manually enter the VIN. The VIN number provides all the details the scanner needs to identify your car precisely.
4. Scan for Fault Codes
With the vehicle information correctly entered, you can now proceed to initiate a fault code scan. Most OBD2 scanners offer options to select specific control units for scanning, or to perform a full system scan which checks all available control units in the vehicle. For a general diagnostic check, a full system scan is usually recommended to ensure no potential issues are overlooked.
If you are unsure how to navigate the scanner’s menus to initiate a scan, consult the device’s integrated help section or the user manual. These resources will provide specific guidance for your particular scanner model.
The duration of a full system scan can vary depending on the car model and the complexity of its electronic systems, typically ranging from a few seconds to several minutes.
5. Interpreting Fault Codes
After the scan is complete, the OBD2 scanner will display any detected fault codes. These codes are the reason why warning lights, such as the check engine light, might be illuminated on your dashboard. Sometimes, fault codes are relatively descriptive and straightforward, such as “C0031-01 – Left Front Wheel Speed Sensor – General Electrical Failure.” This code clearly indicates a potential issue with the left front wheel speed sensor.
However, it’s crucial to understand that fault codes often point to a symptom rather than the root cause of a problem. For example, a common code like “P0171 – System Too Lean (Bank 1)” indicates that the engine’s air-fuel mixture is too lean. While the code identifies the symptom, the underlying cause could be a variety of issues, including a clogged fuel filter, a failing fuel pump, a vacuum leak, faulty sensors (like MAF or O2 sensors), or other problems within the fuel or air intake systems.
Diagnosing the root cause often requires further investigation, potentially involving additional tests and analysis beyond simply reading the fault code.
Pro Tip: Utilizing Live Data for Deeper Diagnostics
Beyond reading fault codes, the ability to access and interpret live data is a powerful feature of OBD2 scanners that can significantly enhance your diagnostic capabilities. Most scanners allow you to view real-time data streams from various sensors and systems while the engine is running.
This live data can be invaluable in pinpointing intermittent problems or understanding system behavior under different operating conditions. For example, if your car is experiencing a lack of power and the only fault code is related to “limp mode” (reduced engine power mode), live data can help you investigate further. You can monitor parameters like fuel pressure, boost pressure (for turbocharged engines), intake airflow, and intake manifold pressure to see if any of these readings are outside of their expected ranges. Deviations in live data can provide crucial clues to the underlying issue.
Alt text: Close up image of an OBD2 scanner screen displaying live data readings during car diagnostics.
However, even with access to fault codes and live data, diagnosing complex automotive issues can be challenging. You may still need to consult repair manuals, online resources, or seek professional help to fully understand the fault codes and effectively troubleshoot the problem.
OBD2 Scanners in Used Car Inspections
The used car market can present potential risks for buyers. Unfortunately, some sellers may not fully disclose a vehicle’s history or pre-existing issues. Used car buyers can use OBD2 scanners as a valuable tool in pre-purchase inspections.
While vehicle history reports, like those from carVertical, can reveal important background information, a physical inspection and a diagnostic scan are essential for a comprehensive assessment, especially when buying a used car.
Always consider using an OBD2 scanner to check for fault codes before purchasing a used vehicle. Hidden fault codes could indicate existing or potential mechanical or electrical problems that might not be immediately apparent during a visual inspection or test drive. If you are unfamiliar with using an OBD2 scanner, or unsure how to interpret the results, it is wise to take the car to a qualified mechanic for a professional pre-purchase inspection. This proactive step can save you from unexpected and costly repairs down the road.
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Clearing Fault Codes: What to Know
Scanning for fault codes is a diagnostic step, but it’s important to remember that simply clearing fault codes without addressing the underlying issue is not a proper repair. Fault codes are indicators of problems, and clearing them only hides the symptom, not the cause.
Even when a diagnostic scan points to a specific component, such as a mass airflow sensor, experienced technicians often perform further tests, like using a multimeter to verify the sensor’s functionality. This is because fault codes can sometimes be triggered by related issues like damaged wiring, loose connections, or corrosion, rather than a faulty sensor itself. Replacing parts based solely on fault codes without thorough verification can lead to misdiagnosis and unnecessary repairs.
After identifying and rectifying the underlying problem, it’s appropriate to clear the fault codes using the OBD2 scanner. After clearing the codes, it’s important to rescan the system to confirm that the fault codes do not reappear. If the codes remain clear, and any related symptoms have been resolved, the issue is likely fixed, and the vehicle is ready for use.
Frequently asked questions
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.
