Dating back to 1995, Diesel engine manufacturers were required to rate thier engines based on their emission levels. Understanding that reducing emissions was the goal and going foward, diesel engine manufacturers were required to meet minimum requirements and those requirements were rated in tiers. The mandate was to reduce emission levels one tier at a time and that time line is shown on the chart below.

June 30, 2015 will be the last day ARB(Air Resources Board) will be accepting registration applications for Interim Tier 4 engines rated 75 bhp and above.

Effectively July 1, 2015, all diesel engines must meet the Tier 4 Final requirements or be a flex engine certified under the flex provision of Federal 40 CFR 1039.625, or Califronia Code of Regulations section 2423 (d).