The Clean Truck Check program, set to implement On-Board Diagnostic (OBD) Monitor Readiness and Permanent Diagnostic Trouble Code (PDTC) requirements starting in early 2025, marks a significant step in reducing emissions and achieving clean air goals. The program addresses key lessons learned from its initial phase in 2023, notably the prevalence of code clearing just before or shortly prior to testing. This code clearing will now result in failed OBD tests as readiness criteria and PDTCs are integrated into the pass/fail determination process. Determining readiness involves evaluating the completion of internal diagnostic tests across various OBD system diagnostics, with readiness limits becoming progressively more stringent over time. Furthermore, Permanent Diagnostic Trouble Codes (PDTCs) require fixing the underlying issues for clearance, emphasizing the importance of vehicle maintenance and performance. As the program unfolds, early testing and avoiding code clearing emerge as crucial strategies for ensuring compliance and minimizing emissions.
Below is the CARB announcement.
New Clean Truck Check OBD Requirements Coming Soon
Starting in early 2024, CARB will begin phasing in On-Board Diagnostic (OBD) Monitor Readiness and Permanent Diagnostic Trouble Code (PDTC) requirements to further reduce emissions and meet clean air goals.
Background
During the initial phase of the Clean Truck Check program in 2023, only vehicles that had their Malfunction Indicator Lamp (MIL) on failed the OBD test. The program did not fail vehicles with active PDTCs or for a lack of OBD Monitor readiness (i.e., completion of internal diagnostic tests). One lesson learned from this early phase of the program testing is that in the absence of minimum readiness requirements, code clearing was prevalent. About 20% of vehicles had OBD codes cleared immediately before, or within a few days, of the test. As readiness criteria and PDTCs are incorporated into the pass/fail determination in 2024, this code clearing will cause a vehicle to fail the OBD test.
Readiness
Readiness is determined by looking at how many of the OBD system diagnostics have been completed and the amount of vehicle operation since codes were cleared (OSC – Operation Since Clear). The OBD system diagnostics are broken down into categories called “Monitors.” Each Monitor must go through a series of diagnostic tests to determine if those systems are working properly. The OBD system reports whether each Monitor has had time to complete its tests; if so, the Monitor is considered “Ready.” The specific number and types of Monitors vary based on OBD protocol (J1939 vs J1979), fuel type, vehicle make, and model year. Based on the tests performed to date, most vehicles have all Monitors ready when compliance tests are submitted. However, vehicles that have had codes cleared recently will have multiple Monitors not ready (incomplete). If too many monitors are incomplete, the vehicle will fail the readiness check. The readiness limits will be phased in and become more stringent over time.
Operation Since Clear
OBD systems store information regarding vehicle operation since codes were cleared. Most vehicles have OSC for:
· Warm-Up Cycles (WUCs) since clear
· Distance traveled, in km, since clear
· Engine run time, in minutes, since clear
Typically vehicles track WUCs and either minutes or distance since clear. Readiness criteria will be applied to the OSC variables provided by an individual vehicle. As they are phased in, the criteria thresholds for these variables will become more stringent over time.
PDTCs
Permanent Diagnostic Trouble Codes (PDTCs) are very similar to regular 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 activated the PDTC, 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.
Getting ready for the Clean Truck Check OBD test
Things to do to have your best chance at passing the Clean Truck Check OBD test:
· If your Malfunction Indicator Lamp (right) is on, get your vehicle repaired as soon as possible.
· Don't wait - Do the OBD test early in the Clean Truck Check compliance window so there will be time to complete the test if there are problems.
· Avoid clearing codes. OBD systems require substantial vehicle operation to be able to complete their emission control diagnostic tests. A vehicle that has not been operated enough, or has too many monitors incomplete, will fail the test. Code clearing can occur when:
o Disconnecting the battery
o Using an improperly installed kill switch that disconnects power to the OBD system [it is OK if the kill switch just cuts power to accessories/lights/etc.]
o Using an OBD scan device to clear codes
For more information, visit https://ww2.arb.ca.gov/obd-readiness-criteria.
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