Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Purpose of the Readiness Tests: Notes
The On-Board Diagnostic (OBD II) system is designed to monitor the performance of emission-related components and report any detected abnormalities in the form of Diagnostic Trouble Codes (DTCs). Since the various components need to be monitored during different driving conditions, the OBD II system is designed to run separate monitoring programs called Readiness Monitors. Many state emissions inspection and maintenance (I/M) programs require that vehicles complete their Readiness Monitors prior to beginning an emissions test.
The readiness monitor status will be reset to incomplete if:
- The battery is disconnected.
- DTCs have been cleared.
- The monitor drive cycle has not been completed.
The monitor status can be checked using an OBD II scan tool. When using hand-held tester, monitor status can be found in the Enhanced OBD II Extended Data List or under CARB OBD II. In the event that any monitors show incomplete, follow the appropriate Readiness Monitor Drive Pattern to change the readiness status to "complete".
| Pattern No. | Readiness Code Patterns |
|---|---|
| 1 | EGR Monitor (Except 1FZ-FE engine) |
| 2 | EGR Monitor (For 1FZ-FE engine) |
| 3 | Catalyst Monitor (Front and rear heated oxygen sensors equipped) |
| 4 | Catalyst Monitor (A/F sensor equipped) |
| 5 | EVAP Monitor (Fuel tank pressure monitor) |
| 6 | EVAP Monitor (Vacuum monitor and LEV II) |
| 7 | EVAP Monitor (Engine RPM monitor) |
| 8 | Heated Oxygen Sensor Monitor (Front and rear heated oxygen sensors equipped) |
| 9 | A/F Sensor and Heated Oxygen Sensor Monitor (Front A/F sensor and rear heated oxygen sensor equipped) |
| 10 | Oxygen Sensor Heater and A/F Sensor Heater Monitor |
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
Rather have a pro handle this?
A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.
No obligation. See pricing before you book.