Yes, it is perfectly safe to scan your car’s computer for diagnostic trouble codes while the engine is running. In fact, in some situations, it can even be beneficial. Let’s delve into why this is the case and what you need to know about scanning your vehicle’s onboard diagnostics system.
To understand why scanning with the engine running is not harmful, we need to look at how your OBD-II (On-Board Diagnostics II) scanner gets its power and communicates with your car’s computer network, also known as the CAN (Controller Area Network) system. Your OBD-II scanner, or dongle, draws power directly from your car’s battery through the OBD-II port. Specifically, pin 16 of the OBD-II port is directly connected to the battery. This means the scanner receives power even when the ignition is switched off.
However, while your OBD-II scanner might be powered on, the car’s CAN system, including various control modules, typically enters a sleep state when the ignition is off. This sleep state is designed to minimize battery drain when the vehicle is not in use. In this sleep state, the primary diagnostic communication module, often called the Gateway module, cannot communicate effectively with other modules in the car.
Turning the ignition to the “ON” position (without necessarily starting the engine) wakes up the CAN system and allows all the modules to communicate with each other. When you initiate a scan, your OBD-II software sends a request through the Gateway module. The Gateway then communicates with each module in the car, requesting a report of any stored fault codes or errors. This process of retrieving diagnostic trouble codes generally works whether the engine is running or not.
Scanning with the Engine Off vs. Engine Running: What’s the Difference?
When you perform a scan with the engine off, you will retrieve all the “historic” fault codes stored in the car’s computer memory. This is often sufficient for identifying past issues. Scanning with the engine off is also the standard practice and minimizes any potential battery drain, although the drain from a quick scan is minimal anyway.
However, scanning with the engine running allows you to go beyond just retrieving stored fault codes. With the engine running, various sensors and systems are actively operating. This means you can access “live data” or real-time parameters from these systems. For example, you can monitor the readings from your oxygen sensors (lambda sensors), engine temperature, RPM, and many other parameters while the engine is running.
Benefits of Scanning with the Engine Running
Scanning while the engine is running is particularly useful for diagnosing intermittent issues or performance problems. If you are experiencing a problem that only occurs when the engine is warm or under load, scanning with the engine running allows you to monitor sensor data in real-time and potentially catch the fault as it happens. This can be invaluable in diagnosing issues that don’t leave permanent fault codes or are related to sensor performance under specific operating conditions.
Furthermore, if you are testing the functionality of specific components, such as oxygen sensors, scanning with the engine running is essential to observe their real-time behavior and ensure they are operating within the expected ranges.
Are There Any Risks to Scanning with the Engine Running?
For modern vehicles, there are virtually no risks associated with scanning with the engine running. The car’s electrical system and diagnostic communication protocols are designed to handle this. The only minor consideration might be a slightly increased battery drain compared to scanning with the engine off, but this difference is negligible for typical scan durations.
Conclusion
In conclusion, scanning your car for diagnostic codes with the engine running is perfectly safe and often advantageous. While scanning with the engine off is sufficient for retrieving stored fault codes, scanning with the engine running unlocks the ability to monitor live data and diagnose performance-related issues in real-time. So, feel confident in using your OBD-II scanner in either scenario to keep your car running smoothly.
