What is a Certified Diesel Emissions Retester?

Certified Diesel Emissions Retesters (or CDERs) are an integral part of Maryland's Diesel Vehicle Emissions Control Program. CDERs are responsible for certifying Safety Equipment Repair Orders (SEROs) that have been issued for diesel vehicles that have failed the emissions test under this Program. Owners who receive such a SERO are required to have their vehicles repaired and retested. Although vehicles can be retested free of charge at designated weigh stations, CDERs employed at private diesel vehicle repair facilities will be the primary individuals responsible for clearing SEROs and certifying compliance with the emission standards.

How do I Become a Certified Diesel Emissions Retester?

Individuals who wish to become Certified Diesel Emissions Retesters (CDERs) will need the authorization of their employers. CDERs will need at least one State-approved smokemeter, a set of wheel chocks, a copy of the applicable regulations and statutes, and a copy of the test procedure SAE J1667. Employers must also have an enclosed testing area that is at least 12 feet wide by 40 feet long. Copies of smokemeter printouts (or "receipts"), Safety Equipment Repair Orders (SEROs), and smokemeter maintenance and calibration records will need to be kept on the premises.

CDERs will be required to work a minimum of 30 hours per week at a facility whose primary business is the repair of on-road heavy-duty diesel vehicles or a State Authorized Station licensed to inspect vehicles over 10,000 pounds.  Although CDERs are required to work a minimum of 30 hours per week, their duties do not need to be restricted to only conducting retests. A shop owner may want to help bring in more business by offering retesting and emissions SERO certification in addition to his/her normal technical services.

Finally, employers must permit periodic scheduled and unscheduled audits by auditors from the Maryland Department of the Environment (MDE). These audits will be primarily focused on the ability of the CDER to perform the necessary functions, the equipment used by the retester, and the keeping of records related to the Program.

Steps to Become a Certified Diesel Emissions Retester

  1. Be employed at least 30 hours per week at a diesel vehicle repair facility that has an enclosed testing area of at least 12 feet wide by 40 feet long. Alternatively, you could work at an Authorized Inspection Station that is licensed to inspect vehicles of over 10,000 pounds gross vehicle or gross combination weight rating.
  2. Have available at your place of employment:

    One of the approved smokemeters approved for use in Maryland

    One set of wheel chocks

    One copy of SAE J1667 test procedure

    One copy of COMAR 11.21.02

    One copy of Maryland Transportation Law, Sections 23-401 to 23-404

    A place to store certified Safety Equipment Repair Orders, smokemeter maintenance and calibration records, and smokemeter printouts or "receipts" 

  3. Acquire an application from the Automotive Safety Enforcement Division (ASED) or MDE to become a CDER (to be submitted at the time of the exam mentioned under 5) or from MDE's web site.
  4. Properly fill out the application - applications that are incomplete or unreadable will be refused.
  5. Study the written materials listed under 2) in preparation for an exam given by ASED on the third Friday of every month.
  6. Determine which ASED exam session you wish to attend and show up on time - no appointment is necessary.
  7. Submit your application to the ASED Trooper at the time of the exam.
  8. Receive a score of at least 80 percent on the ASED written exam - you will be notified of your examination score the same day you take the exam.
  9. Contact MDE's Mobile Sources Control Program at (410) 537-3270 to set up a time to have an MDE representative come to your place of employment to administer a functional test.  You will be required to know how to operate the equipment to successfully complete a retest and to properly fill out and keep in proper order all necessary paperwork (Safety Equipment Repair Orders (SEROS), smokemeter, calibration/repair log, and smokemeter receipts.  You will also be required to have a diesel vehicle with a gross vehicle weight rating or gross combination weight rating of more than 10,000 pounds available in order to demonstrate your ability to conduct a retest to the MDE representative.
  10. Successfully complete the functional test.  You will be provided with a certificate at this time, with which you will be authorized to conduct retests and certify Safety Equipment Repair Orders issued for diesel emissions violations.  Note: retests can only be performed at your place of employment and with the consent of your employer. 
  11. As a Certified Diesel Emissions Retester (CDER) you will be subject to scheduled and unscheduled audits conducted by auditors from the Maryland Department of Environment.  In order to "pass" an audit, equipment must be maintained according to the manufacturer's specifications and the SERO's, smokemeter calibration/repair log, and smokemeter printouts must be keep in chronological order and have been properly completed.  As a CDER, you are also responsible for immediately notifying the Automotive Safety Enforcement Division and the Maryland Department of Environment of any changes in employment.


Contact Information

For additional information, call Tim Shepherd at (410)537-3270 or email tim.shepherd@maryland.gov.​


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