While your Nissan Xterra had engine work done they may have disconnected the battery (erasing the Emission Monitors). The emission monitors are internal self tests which the ECU conducts to ensure the main emission systems are functioning properly.
You want to drive your Xterra approximately 100-200 miles in order for the ECU to complete the self-tests and set the Monitors. The following is a Generic Drive Cycle.
Begin by: (Make sure you have between 1/4 and 3/4 fuel in the gas tank. The EVAP test will not run while your Nissan has a full tank of gas or the gas tank is near empty) .
- 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.
- 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 should set the emission monitors (also known as "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. Take caution when performing drive cycles on public roadways.
