How to Lower NOX That Is Too High

1). Put on the gloves and goggles for safety. Ensure that the engine has not run for four or five hours. The EGR valve can be hot if you attempt to remove it after operating the engine.
2). Consult the owner's manual of your vehicle to identify the position of your car's intake system. Once you have done that, locate the EGR valve. It has a shape resembling a mushroom.
3). Detach the vacuum hose and electrical connector attached to the EGR valve by unclamping them from the valve.
4). Unscrew the two bolts found on the side of the valve with a wrench that corresponds with the size of the bolts. Disconnect the pipe underneath the valve using a wrench that corresponds with the size of the pipe.
5). Inspect the passages of the EGR valve. If there is heavy carbon buildup inside the passages, gently use the scratch awl to clear out the carbon deposits. This is the likely cause of the high NOx reading and won't require a new EGR valve. If you find little to no carbon deposits, the EGR valve itself is likely damaged and must be replaced.
6). Return the old valve or put the new valve back in position. Reattach the pipe and volts. Clamp the vacuum hose and electrical connector back in their original positions.