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.
Read the readiness code
Read off diagnostic trouble codes (DTCs) and the readiness status.
If readiness is "OK" and no diagnostic trouble codes are stored, two cycles have run, i. e. the system's diagnostic functions have run two times without detecting a fault.
HINT: Readiness is reset (to "NOT OK") when the diagnostic trouble codes are cleared or if power is cut off to the engine control module (ECM).
US government information (US only)
The United States Environmental Protection Agency (EPA) has issued a guidance letter, "Performing On Board Diagnostic System checks as Part of a Vehicle Inspection and Maintenance Program" (EPA420-R-01-015 June 2001), that incorporates various implementation issues associated with OBD-I/M testing. One being that the EPA has revised the readiness criteria to allow states to not reject MY 1996-2000 vehicles with two or fewer unset readiness codes, or MY 2001 and newer vehicles with no more than one unset readiness code. As mentioned herein this is suggested practice. Each individual state may abide by this guidance or enforce state regulations suited to their individual environmental needs. Please consult your State Department of Motor Vehicle for your current I/M testing regulations and procedures.
Select the appropriate remedy depending on this status:
- If diagnostic trouble codes (DTCs) are stored
Refer to Diagnostic Trouble Code (DTC) stored
- If readiness is "NOT OK".
- If readiness is "OK" and no diagnostic trouble codes (DTCs) are stored.
OKAY: Troubleshooting has been completed.
Use the Manual With the Right Hardware
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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.
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