It sounds like your 2003 Hyundai Elantra failed the smog check because one or many Emission Monitors has been erased when your changed the battery.
The Generic OBD II Drive Cycle below will more then likely be sufficient in setting your Hyundai Elentras emission monitors (such as the EVAP monitor, CAT monitor, Oxygen Sensor monitor) the necessary emission monitors. This OBDII drive cycle begins with a cold start (coolant temperature below 122 degrees F). We recommend achieving this by letting your Hyundai cool down overnight, and beginning the drive cycle process the next day. Take extra caution while performing drive cycles on public roadways. Drive cycles can be difficult to follow under normal driving conditions.
Begin by:
- Start the engine. Idle the engine in drive for two and a half minutes with the A/C and rear defroster on.
- Turn the A/C and rear defrost off, and accelerate to 55 mph at half throttle.
- Hold at a steady speed of 55 mph for three minutes.
- Decelerate (coast down) to 20 mph without braking or depressing the clutch.
- Accelerate back to 55 to 60 mph at ¾ throttle.
- Hold at a steady speed of 55 to 60 mph for five minutes.
- Decelerate (coast down) to a stop without braking.
If all other emissions systems are functioning properly, completing the drive cycle above will set the "readiness flags" required to pass the smog check. It will not hurt to perform the drive cycle 2 or 3 times before the smog inspection.
