"Monitor Status Since DTCs Cleared" vs "Monitor Status This Drive Cycle"

When using an OBD2 scanner to check your vehicle's readiness for a smog test, you might come across two different monitor statuses:

• Monitor Status Since DTCs Cleared
• Monitor Status This Drive Cycle

These two sections often cause confusion, especially when preparing for an emissions or smog test.

What Do They Mean?

• “Since DTCs Cleared” shows the results of all onboard diagnostic monitors since the last time diagnostic trouble codes (DTCs) were cleared or the battery was disconnected. This is the standard reference used for emissions testing.
• “This Drive Cycle” resets every time the key is turned off and on again. It only reflects what has happened during the current ignition cycle, which makes it less relevant for smog testing purposes.

How to Prepare for a Smog Test

If monitors under "Since DTCs Cleared" are not complete or show failure, the vehicle may not pass a smog test. Here's how to address this:

1. Follow a proper drive cycle procedure, which usually involves a mix of highway and city driving with specific speed and idle times.
2. Re-scan the vehicle and focus on the “Since DTCs Cleared” section.
3. If most or all required monitors now show “Complete”, your vehicle is likely ready for inspection.

What to Ignore

Even if the “This Drive Cycle” section still shows failures, they typically do not affect smog testing results. This is because they only reflect temporary conditions from the most recent key cycle.

Summary

• Focus on "Since DTCs Cleared" for emissions readiness.
• Ignore "This Drive Cycle" unless you're troubleshooting live issues.
• Always complete a proper drive cycle after clearing codes or disconnecting the battery.