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On-Board Diagnostic (OBD) Readiness Criteria

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OBD Readiness Criteria

Current Criteria

  • No Diagnostic Trouble Codes (DTCs) shall be present and vehicles must have at least five (5) Warm-Up Cycles (WUC) since codes clear (SCC).

Upcoming Criteria (End of May 2025)

No DTCs/Permanent DTCs (PDTCs) shall be present and vehicles must have:

  • at least five (5) WUC SCC, or
  • at least 200 miles travelled SCC, or
  • at least 400 minutes engine run time SCC, or
  • at most two (2) incomplete OBD Monitors.

If a PDTC is present, the Code will be ignored if the vehicle has:

  • at least 15 WUC SCC, or
  • at least 400 miles travelled SCC, or
  • at least 800 minutes engine run time SCC, or
  • at most one (1) incomplete OBD Monitor.

An OBD test submitted to the Clean Truck Check that does not meet the above criteria will get a Not Ready test result and will not meet the emissions compliance testing requirements. If your vehicle receives a “Not Ready” OBD test result, you should continue operating the vehicle under normal business practices for a few days and then have the vehicle retested.

Background

On-Board Diagnostic (OBD) systems are self-diagnostic systems incorporated into the computers of vehicles that monitor virtually every component that can affect vehicle emissions. If a problem with an emissions-related component is detected, the OBD system illuminates a warning lamp on the vehicle instrument panel to alert the driver and also stores information about the detected malfunctions to aid any needed repairs.

For these OBD systems to accurately monitor and detect emissions related problems, the vehicle must be operated a sufficient amount of time for the system to complete a full diagnostic monitoring cycle of each component it is monitoring. Once this occurs, the OBD system is in a ready state to accurately determine whether a vehicle has an emissions related performance issue or not. If a vehicle’s OBD system has been reset or recently cleared, also referred to as “code clearing,” it will take time and operation to bring the vehicle’s OBD system back into a fully ready state; i.e., all vehicle OBD monitors in the ready state meaning the OBD system has operated sufficiently to determine the presence or absence of a DTC. Often a reset of the OBD system happens when the battery is disconnected or a scan tool is used to perform a code clearing.

The Clean Truck Check OBD readiness testing requirement is an adjustment for some vehicle owners. Understanding this, the program will ease into this OBD readiness requirement ramp up as the program matures. Until this time, the program will establish minimum operation thresholds that will increase in stringency until these full readiness requirements are achieved.

What is a warm-up cycle?

A warm-up cycle means driving a vehicle so that the engine coolant temperature rises by at least 40 degrees Fahrenheit after the engine is started and reaches at least 140 degrees Fahrenheit for diesel engines (160 degrees for natural gas engines).

What are Permanent Diagnostic Trouble Codes?

Permanent Diagnostic Trouble Codes (PDTCs) are very similar to regular Diagnostic Trouble Codes (DTCs). However, unlike regular DTCs, they cannot be reset by disconnecting the vehicle’s battery or cleared using an OBD scan device. The only way to clear a PDTC is to fix the underlying problem with the vehicle that originally caused the PDTC to set, and then allow the vehicle sufficient drive time to re-run the Monitor that identified the problem in the first place. When the Monitor runs without identifying a problem, the PDTC will clear itself.