Smog Check Readiness Monitors Explained
OBD-II 'readiness monitors' are self-tests your vehicle runs while driving. They must be 'complete' to pass California smog. Battery disconnect, code clearing, or low fuel can reset them — requiring 50-100 miles of mixed driving to recomplete.
Key facts
- ✓ Readiness monitors = OBD-II self-tests (Catalyst, EVAP, O2 sensors, etc.)
- ✓ Must be COMPLETE to pass smog — California rejects 'NOT READY' vehicles
- ✓ Disconnecting battery resets them — drive 50-100 mixed miles to recomplete
- ✓ Clearing codes resets them — same fix: drive more
- ✓ Hybrid/EV-specific monitors are NOT required for hybrid testing
What to do
- If you recently disconnected battery or cleared codes: drive 50-100 mixed miles before testing
- Mix of highway (30+ min at 55+ mph) and city (stop-and-go)
- Multiple cold starts help (let car sit overnight, drive next morning)
- Avoid: lots of stop-and-go-only driving, very short trips
- Bring vehicle to our shop — we can pre-scan readiness status free for first-time customers
Most common causes
- Recent battery disconnect (most common)
- Mechanic recently cleared codes
- ECU reflash or tune update
- Vehicle sat unused for weeks
- Constant short trips (engine never reaches operating temp)
Common questions
How many readiness monitors must be complete?
California allows ONE 'incomplete' for 1996-1999 vehicles, ZERO incomplete for 2000+ vehicles. Most failures are catalyst, EVAP, or O2 sensor monitors not yet complete.
How do I check readiness status myself?
Plug an OBD-II scanner (or borrow one from AutoZone, $0) into the dash port — most scanners show readiness status. Or visit our shop for a free pre-test scan.
Why are my monitors stuck on 'not ready'?
Could be: vehicle hasn't been driven enough since reset, specific driving cycle not completed (e.g., EVAP requires specific fuel level + driving pattern), or a hardware issue (failed sensor) preventing the test from completing.