For many car owners and DIY mechanics, the ability to clear diagnostic trouble codes (DTCs) is a key function of OBD2 scanners. But can an OBD2 scanner clear all types of codes, and what are the nuances involved? As an auto repair expert at obd-de.com, let’s delve into the different types of DTCs and clarify the capabilities of OBD2 scanners when it comes to code clearing.
It’s crucial to understand that not all DTCs are created equal. According to automotive repair guidelines, specifically from sources like the Bureau of Automotive Repair (BAR), some codes are designed to be more persistent than others. This persistence is directly related to the nature and severity of the fault detected by your vehicle’s onboard diagnostic system.
Permanent Diagnostic Trouble Codes (PDTCs): The Unclearable Codes
Permanent Diagnostic Trouble Codes (PDTCs) are a special category of DTCs that, unlike regular codes, cannot be simply erased using an OBD2 scanner or by disconnecting your car battery. This is a critical distinction to grasp.
The very nature of a PDTC is to remain in your vehicle’s computer memory until the underlying issue that triggered the code is properly fixed and the vehicle verifies the repair through its diagnostic monitors. As BAR clearly states, “The only way to clear a PDTC is to fix the underlying problem with the vehicle that originally caused the PDTC and its corresponding DTC to set, and then allow the vehicle sufficient drive time to re-run the monitor that identified the problem in the first place. When the monitor runs without identifying a problem, the PDTC will clear itself.”
Essentially, if you’re facing a PDTC, simply using an OBD2 scanner to attempt a reset will be futile. The scanner might indicate a successful clearing process, but the PDTC will immediately reappear. This is because the root cause of the problem still exists. PDTCs are designed to ensure that vehicle owners address genuine issues affecting emissions or vehicle performance, rather than just masking symptoms. Therefore, the focus must be on accurate diagnosis and repair of the fault that initiated the PDTC in the first place.
Pending Diagnostic Trouble Codes: Waiting in the Wings
Pending DTCs, sometimes referred to as intermittent DTCs, represent a different scenario. These codes are set when the vehicle’s Powertrain Control Module (PCM) detects a potential fault, but it needs further verification before setting a full, active DTC and potentially illuminating the check engine light.
Pending codes often arise from faults that occur sporadically or from conditions that need to be observed over multiple driving cycles. The PCM is programmed to monitor for these faults over a specific number of warm-up cycles. A “warm-up cycle” generally refers to the engine reaching its normal operating temperature and then cooling down.
If the intermittent fault does not reoccur within approximately 40 warm-up cycles, the pending code will typically be automatically cleared from the PCM’s memory. However, if the fault persists or reappears within this timeframe, the pending code can “mature” into a regular DTC. This maturation process often involves the PCM detecting the fault in two consecutive warm-up cycles. Once matured, the DTC will likely trigger the check engine light, alerting the driver to a persistent issue.
OBD2 scanners can typically read and clear pending codes. Clearing a pending code with a scanner might seem like a quick fix, but it’s essential to understand that if the underlying issue is still present, the pending code, or potentially a more serious DTC, is likely to return. Treating pending codes as early warning signs and investigating potential problems is a proactive approach to vehicle maintenance.
History Diagnostic Trouble Codes: Records of Past Issues
History DTCs, also known as “inactive” or “memory” codes, provide a valuable record of past faults that were once active but are no longer currently detected. Think of them as a log of previous issues that your vehicle has experienced and, in many cases, resolved.
The behavior of history codes regarding clearing varies depending on the specific code and vehicle manufacturer. Some history codes can be readily cleared using an OBD2 scan tool during a standard code clearing procedure. Others might require a “double code clearing” process, which involves performing the clearing function twice in succession.
Furthermore, certain history codes are designed to be more persistent and will only clear after a predetermined number of ignition cycles or drive cycles have been completed, and specific operating conditions are met. This persistence is often built in for codes related to systems that require rigorous testing to ensure proper functionality.
The purpose of retaining history codes is to aid in diagnosing intermittent problems. If a vehicle has experienced an issue in the past that then disappeared, the history code can provide crucial clues for technicians when troubleshooting recurring or related problems. For codes that are resistant to clearing, consulting the vehicle’s service manual is essential. The manual will specify the conditions and procedures required to clear the history code effectively. Often, these procedures involve driving the vehicle under specific conditions to allow the diagnostic monitors to run and confirm that the fault is no longer present.
Conclusion: OBD2 Scanners and Code Clearing Realities
In summary, while OBD2 scanners are valuable tools for reading and clearing many types of diagnostic trouble codes, their ability to clear codes is not universal.
- Yes, OBD2 scanners can clear many regular DTCs and pending DTCs. This can be helpful after repairs are made to turn off the check engine light and confirm the fix.
- No, OBD2 scanners cannot clear Permanent DTCs (PDTCs). These codes are designed to remain until the underlying problem is resolved and verified by the vehicle’s system.
- History DTCs present a mixed bag. Some can be cleared easily, while others require specific procedures or will clear automatically over time.
Understanding the different types of DTCs and the limitations of code clearing is essential for effective vehicle maintenance and repair. Using an OBD2 scanner responsibly involves not just clearing codes, but also diagnosing the root cause of problems and ensuring proper repairs are performed. Simply clearing a code without addressing the underlying issue is often a temporary fix and can lead to more significant problems down the road. Always prioritize accurate diagnosis and repair over simply making warning lights disappear.
