The dreaded words “OBD2 Monitor Incomplete” can be a major headache when you’re trying to get your car inspected or diagnose an issue. You plug in your OBD2 scanner, hoping for a clean bill of health, but instead, you’re met with the frustrating message that some monitors are not ready. This doesn’t necessarily mean there’s something wrong with your car right now, but it does mean your vehicle’s onboard diagnostic system hasn’t finished all its self-tests. So, why does your OBD2 test keep saying incomplete, and what can you do about it? Let’s dive into the common causes and solutions.
Understanding OBD2 Readiness Monitors
To understand why your OBD2 test might be incomplete, it’s crucial to know about readiness monitors. These are self-tests that your car’s computer (Engine Control Module or ECM) performs on various emission control systems. Think of them as health checks for your car’s pollution control equipment. These monitors ensure systems like your catalytic converter, oxygen sensors, evaporative system, and EGR system are functioning correctly. When these monitors are “ready” or “complete,” it signifies that these systems have been tested and are working as expected, or at least haven’t reported any failures recently.
There are different types of readiness monitors, broadly categorized into:
- Continuous Monitors: These run constantly during normal driving. Examples include Misfire, Fuel System, and Comprehensive Components.
- Non-Continuous Monitors: These require specific driving conditions to run and complete their tests. Examples include Catalyst, Evaporative System, Oxygen Sensor, EGR, and others.
It’s the non-continuous monitors that often cause the “incomplete” issue, as they need specific parameters like speed, engine temperature, and driving time to activate and finish their diagnostic routines.
Common Reasons for Incomplete OBD2 Monitors
Several factors can lead to your OBD2 test showing incomplete monitors. Here are some of the most frequent culprits:
1. Recent Battery Disconnection or Diagnostic Trouble Code (DTC) Reset
This is the most common reason for incomplete monitors. Whenever your car’s battery is disconnected or Diagnostic Trouble Codes (DTCs) are cleared using a scan tool, the readiness monitors are reset to an “incomplete” state. This is because the ECM’s memory of completed tests is erased. This is normal, and your car needs to re-run these tests.
Solution: If you’ve recently had battery work or cleared codes, you simply need to drive your car. Normal driving over a few days usually allows most monitors to complete.
2. Not Enough Driving or Incorrect Driving Conditions (Drive Cycles)
As mentioned earlier, non-continuous monitors need specific driving conditions to run. If your daily driving doesn’t include these conditions, some monitors might remain incomplete. Manufacturers design specific drive cycles – a set of driving conditions – to help complete these monitors quickly. These drive cycles often involve a combination of highway and city driving, specific speeds, and durations.
Solution: Consult your vehicle’s owner’s manual or a repair manual for the specific drive cycle for your car make and model. Performing the correct drive cycle can often set the monitors to “ready.” However, be sure to perform drive cycles safely and legally.
3. Underlying Vehicle Problems
Sometimes, an incomplete monitor can indicate an actual problem preventing the monitor from running or completing. If there’s a fault in a system, the corresponding monitor might not be able to finish its self-test and will remain incomplete. This could be related to issues with sensors, actuators, or other components within the emission control system.
Solution: Use an OBD2 scanner to check for pending or stored Diagnostic Trouble Codes (DTCs). Even if your check engine light isn’t on, there might be pending codes that are preventing monitors from completing. Address any DTCs you find. If no DTCs are present, a more thorough diagnostic process might be needed to pinpoint the issue preventing monitor completion.
4. Vehicle-Specific Issues and Design Anomalies
Certain vehicle makes and models are known to have issues setting specific monitors, even under normal driving conditions. This could be due to software glitches, design anomalies, or overly sensitive monitoring systems. In some cases, manufacturers release Technical Service Bulletins (TSBs) or software updates to address these issues.
Solution: Research if your car make and model is known to have issues with OBD2 monitor readiness. Online forums, repair databases, and websites like techcarusa.com can be valuable resources. Check for any TSBs or recalls related to OBD monitor issues for your vehicle. Sometimes, a software update from the dealer is required. In some rare cases, particularly with older vehicles or certain heavy-duty vehicles, the OBD system design might be such that certain monitors are not expected to be always “ready” under all circumstances, and inspection systems are designed to accommodate this (as seen in the original article’s tables for specific vehicle exceptions).
5. Permanent Diagnostic Trouble Codes (PDTCs)
Vehicles from model year 2010 and newer are equipped with Permanent Diagnostic Trouble Codes (PDTCs). These codes are similar to regular DTCs but cannot be cleared by simply using a scan tool or disconnecting the battery. PDTCs are designed to ensure that a fault is properly repaired and verified before the code is cleared. If a PDTC is present, it can sometimes interfere with readiness monitors.
Solution: If a PDTC is present, it needs to be addressed. Often, this requires proper diagnosis and repair of the underlying issue that triggered the code. Once the repair is done and the system verifies the fix, the PDTC should clear itself after a number of drive cycles.
Troubleshooting Incomplete OBD2 Tests
Here’s a step-by-step approach to troubleshooting why your OBD2 test keeps saying incomplete:
- Check for Diagnostic Trouble Codes (DTCs): Use an OBD2 scanner to check for any stored or pending DTCs. Address any codes present, as they might be the reason for the incomplete monitors.
- Perform a Drive Cycle: Consult your owner’s manual or a reliable repair source for the specific drive cycle for your vehicle. Execute the drive cycle carefully and safely.
- Drive Normally for a Few Days: If a drive cycle doesn’t immediately set the monitors, simply drive your car under normal conditions for a few days. Vary your driving – include both city and highway driving if possible.
- Re-scan for Readiness: After driving for a while, use your OBD2 scanner again to check the readiness monitor status.
- Investigate Vehicle-Specific Issues: If monitors are still incomplete after driving and performing drive cycles, research if your vehicle is known to have OBD monitor issues. Look for TSBs, recalls, or online discussions related to your car model.
- Seek Professional Help: If you’ve tried the above steps and monitors remain incomplete, it’s best to consult a qualified mechanic. They can perform a more in-depth diagnosis to identify any underlying mechanical or electrical issues preventing monitor completion. They can also advise on vehicle-specific issues and potential software updates.
When Incomplete Monitors Are Acceptable
It’s important to note that in some situations, having a few incomplete monitors is acceptable, especially for older vehicles. Smog check regulations in many areas allow for one or two incomplete monitors depending on the model year and fuel type of your vehicle. For example, for gasoline vehicles from model year 2000 and newer, typically only the Evaporative System monitor can be incomplete to pass a smog check. For diesel vehicles, the rules may be different. Always check your local smog check regulations to understand the specific requirements in your area.
| Model Year | Fuel Type | Number of Incomplete Monitors Allowed (for Smog Check in some regions) |
|---|---|---|
| 1996-1999 | Gasoline | One |
| 2000 and newer | Gasoline | Evaporative System only |
| 1998-2006 | Diesel | Zero |
| 2007 and newer | Diesel | Particulate Filter and NMHC only |
Note: Regulations can vary by location. Always verify local requirements for emissions testing.
Conclusion
Seeing “OBD2 Test Incomplete” can be concerning, but understanding the reasons behind it can help you take the right steps. Often, it’s simply a matter of driving your car enough to allow the monitors to complete. However, persistent incomplete monitors can sometimes indicate underlying issues that need attention. By following the troubleshooting steps and seeking professional help when needed, you can address the issue and ensure your vehicle is running efficiently and cleanly. And remember to always consult resources like techcarusa.com for more in-depth information and vehicle-specific guidance on OBD2 systems and automotive diagnostics.
