Performing a car diagnostic used to require a trip to the mechanic, but with the advent of OBD2 scanners, you can now troubleshoot many car issues from the comfort of your own garage. Learning how to run diagnostic on car with code reader is a valuable skill for any car owner, potentially saving you time and money. This guide will walk you through the process, making it easy to understand and use this powerful tool.
The first step in running a diagnostic is locating your vehicle’s OBDII port. In almost every passenger car manufactured since 1996, you’ll find a standardized 16-pin Diagnostic Link Connector (DLC), commonly referred to as the OBDII port. The most frequent location for this port is underneath the dashboard on the driver’s side. You’ll typically find it near the steering column or around the area above the pedals. While the driver’s side dashboard is the most common location, there are instances where manufacturers might place it in slightly different spots. Don’t be surprised if you find it tucked away in the center console or even under the passenger side dashboard in some vehicle models. It’s designed as a female connector with a distinctive trapezoidal shape, making it easily identifiable.
Connecting your OBD2 scanner is designed to be straightforward. The male plug on your code reader is engineered to fit the OBDII port in only one orientation, eliminating guesswork. Simply align the trapezoidal shape of the scanner’s plug with the port under your dashboard. Then, gently but firmly push the two connectors together. You might encounter slight resistance, and a little wiggle can sometimes help ensure a complete and secure connection.
To properly connect an OBD2 scanner and initiate a diagnostic session, follow these steps in order:
- Turn off the ignition completely. Ensure your car’s engine is off and the key is in the “off” position. This is a crucial safety step and ensures proper communication between the scanner and your car’s computer.
- Connect the scan tool to the diagnostic port. Plug the OBD2 scanner into the OBDII port you located earlier. Make sure it’s firmly seated.
- Turn the ignition to the “on” position, without starting the engine. Turn your key to the position just before starting the engine. This is often referred to as the “key on, engine off” (KOEO) position. This action powers up your car’s electrical systems and the OBDII port.
- Wait for the scan tool to power up. In most cases, the OBD2 port itself provides power to your scan tool. Once connected and the ignition is in the “on” position, the scanner should automatically turn on.
- Allow the device to complete its boot sequence. Like any electronic device, your OBD2 scanner needs a moment to start up. Wait until it has fully booted up and displays its main menu or prompts.
Once the scanner has booted up, it will usually guide you through any additional information it requires. This might include prompting you to input your vehicle’s engine size, Vehicle Identification Number (VIN), or instructions on whether to start the engine for certain tests.
Navigating the Menu Options
After successfully connecting your OBD2 scanner and it has completed its start-up process, you’ll be presented with a menu on its display screen. The options available in this menu can vary based on whether you are using a basic code reader or a more advanced diagnostic scan tool. Advanced devices often offer more comprehensive system monitoring and testing capabilities. However, common options you can expect to find typically include some or all of the following:
- Read Codes: Selecting this option is the primary function for most users. It instructs the scanner to retrieve and display any Diagnostic Trouble Codes (DTCs) that are currently stored in your vehicle’s computer system. Along with the DTC number, many scanners will also provide a brief text description of the fault. If there are multiple codes, the scanner will usually scroll through each of them.
- Erase Codes: This menu option allows you to clear or reset the Diagnostic Trouble Codes that are stored in your car’s computer. When selected, the scanner will typically ask for confirmation to prevent accidental code deletion. It’s important to understand that erasing codes clears the fault data and can turn off the Check Engine Light, but it doesn’t fix the underlying problem that caused the code in the first place.
- Live Data: This feature, available on scanners with live data monitoring capabilities, allows you to view real-time readings from your vehicle’s sensors and systems. You can scroll through a list of parameters, such as engine temperature, RPM, oxygen sensor readings, and more, to see if they are within normal operating ranges. This is invaluable for diagnosing intermittent issues or observing sensor behavior in real-time.
- Freeze Frame: Freeze Frame data captures a snapshot of various engine parameters at the precise moment a DTC was set. This information is extremely helpful for diagnosing the conditions under which a fault occurred. It provides valuable context, such as engine speed, engine load, and sensor values at the time of the fault.
- Vehicle Info: This option typically displays basic information about your vehicle, which is pulled from the car’s computer system. This may include the VIN, calibration IDs, and other vehicle-specific data.
- I/M Readiness: “I/M” stands for Inspection and Maintenance. This section is particularly useful for emissions testing or smog checks. It displays the readiness status of various emission-related systems in your vehicle. It indicates whether these systems have completed their self-tests and are ready for an emissions test. If any system shows as “not ready,” it could indicate a problem that might prevent your vehicle from passing a smog check.
Most OBD2 scanners are equipped with buttons to navigate through the menus. Even Bluetooth or Wi-Fi enabled scanners, which are controlled via smartphones, will have on-screen buttons or intuitive interfaces. Arrow buttons are generally used to scroll through menu options, and a selection button is used to confirm your choice. A “back” or “escape” button is usually included to navigate back to the previous menu screen.
Deciphering Diagnostic Trouble Codes (DTCs)
OBD-II scanner displaying diagnostic trouble codes
When you select the “Read Codes” option on your OBD2 scanner, it will retrieve and display any stored Diagnostic Trouble Codes (DTCs). Sometimes, a brief description of the fault might appear on the screen, but often you will only see the code itself. DTCs follow a standardized format: a single letter followed by four numerical digits, such as P0301.
The initial letter of the DTC provides the first level of system identification, indicating which vehicle system is experiencing the fault:
- P (Powertrain): “P” codes relate to issues within the powertrain system. This is the most common category and includes problems with the engine, transmission, fuel system, and emission control systems.
- B (Body): “B” codes indicate problems with the body control systems. This can encompass a wide range of issues related to the vehicle’s interior and body functions, such as airbags, power windows, central locking, and comfort or convenience features.
- C (Chassis): “C” codes refer to problems within the chassis systems. These codes relate to systems like the anti-lock braking system (ABS), traction control, electronic stability control, suspension, and power steering.
- U (Network/Communication): “U” codes denote network communication issues. These codes indicate problems with the communication network within the vehicle, often involving the Controller Area Network (CAN) bus or other communication protocols between different electronic control units (ECUs).
The numerical digits that follow the letter provide further detail about the specific fault. The very first number (the second character in the DTC) is either a ‘0’ or a ‘1’.
- 0: If the second character is ‘0’, it signifies a generic or standard code. Generic codes are defined by the Society of Automotive Engineers (SAE) and are common across virtually all vehicle manufacturers.
- 1: If the second character is ‘1’, it indicates a manufacturer-specific code. These codes are defined by the specific car manufacturer and may have a more detailed or nuanced meaning compared to generic codes.
The third digit in the DTC provides even finer system identification:
- 1: Fuel and Air Metering
- 2: Fuel and Air Metering (Injector Circuit)
- 3: Ignition System or Misfire
- 4: Auxiliary Emission Controls
- 5: Vehicle Speed Control & Idle Control System
- 7, 8, 9: Transmission related codes
- A, B, C: Hybrid Specific Codes
The final two digits (fourth and fifth positions) are used to pinpoint the specific component or circuit that is malfunctioning within the identified system. There are hundreds of potential combinations for these last two digits, each with a corresponding fault description.
Let’s revisit our example code, P0301. Breaking it down:
- P: Powertrain system.
- 0: Generic code (common to all manufacturers).
- 3: Ignition system or misfire.
- 01: Specifically identifies cylinder #1.
Therefore, P0301 indicates a generic powertrain code related to the ignition system, specifically a misfire detected in cylinder #1.
Saving Money with DIY Diagnostics
Using an OBD2 reader offers several ways to save money on car repairs and maintenance. Firstly, if your Check Engine Light illuminates or you experience a performance issue, a quick scan can provide an initial indication of the potential problem area. While it doesn’t give you a definitive diagnosis, it’s a crucial first step in understanding what might be wrong.
Secondly, an OBD2 scanner can help you determine if your vehicle is likely to pass an upcoming smog check. The I/M Readiness test can reveal if there are any emission-related faults that could cause your vehicle to fail. Addressing these issues beforehand can save you the cost and inconvenience of a failed smog test and re-test fees.
Furthermore, by using an OBD2 scanner, you can potentially save money on both diagnostic fees and repair costs if you are comfortable performing some repairs yourself. For instance, if a scan reveals a code like P0138, indicating a “bank 1 sensor 2 oxygen sensor high voltage,” it often suggests a faulty oxygen sensor. Oxygen sensors are typically a DIY-friendly replacement. By identifying the faulty sensor yourself with the code reader and replacing it, you can avoid diagnostic charges at a repair shop and potentially save on labor costs for the repair. After replacing the sensor, you can use your OBD2 scanner to clear the code and confirm the issue is resolved.
Consider investing in an OBDII scanner to expand your DIY car repair capabilities and take a more proactive approach to vehicle maintenance. Alternatively, explore options like AutoZone’s Loan-A-Tool program, where you can borrow a scan tool at no cost, making car diagnostics accessible to everyone.
FAQ/People Also Ask
How do you use OBD II scanner?
To use an OBDII scanner, locate the OBDII port under your car’s dashboard, plug the scanner into the port, turn your car’s ignition to the “on” position (without starting the engine), and then follow the on-screen prompts on the scanner to read diagnostic codes and perform other functions.
Does car have to be running to use OBD2 scanner?
No, in most cases, the car does not need to be running to use an OBD2 scanner for reading trouble codes. You typically only need to turn the ignition to the “on” position (KOEO) to power up the scanner and the car’s computer system for diagnostics.
How do I read my OBD scanner?
To read your OBD scanner, navigate to the “Read Codes” option in the scanner’s menu. The scanner will then display any active and pending diagnostic trouble codes (DTCs). Note down these codes. The first letter of the code indicates the system affected (P=Powertrain, B=Body, C=Chassis, U=Network), and the numbers provide more specific information about the fault.
Can you plug in OBD scanner while car is running?
While it is technically possible to plug in an OBD scanner while the car is running, it is generally not recommended. It’s best practice to turn the ignition off before connecting or disconnecting an OBD2 scanner. If you need to perform tests with the engine running (like monitoring live data), connect the scanner with the ignition off, then start the car after the scanner is connected and powered up.
