NJ-CERT Module 5 - OBD Repair - Common Failure Reasons, Challenging Cases, and Repair Strategies

Oct 23, 2026

NJ-CERT Module 5 explains New Jersey OBD inspection testing for eligible vehicles, outlining the process from KOEO/KOER checks through DLC verification, communications attempts, and readiness evaluation. It describes how the inspection workstation reads the vehicle’s OBD computer to confirm the emissions-related system and the OBD system’s proper function, capturing identification data for fraud detection. The module specifies gasoline, diesel, and other fuel applicability by model year and GVWR cutoffs and details common MIL and DTC-related failure points.

LanguageEnglish

CategoryExam

FormatPDF

Pages47

Reading Time1 h 58 min

AccessFree to download

Part 1 - New Jersey’s OBD Inspection Test Components and Process

NJ’s OBD Test – The Basics

OBD Testable Vehicles

OBD Test Components

OBD Test Sequence-Steps 1 & 2

OBD Test Sequence – Step 3

OBD Test Sequence – Step 4

OBD Test Sequence – Step 5

NJ-CERT Module 5: OBD Repair: Common Failure Reasons, Challenging Cases, and Repair Strategies A course made for New Jersey’s Certified Emission Repair Technician (ERT) Presented by the NJ Department of Environmental Protection (NJDEP) Bureau of Mobile Sources • Note: If you have not printed out the Master Acronym List, please do so now OR have it open while viewing these Modules . • For detailed rules and regulations, please visit Section 2 on the NJ-CERT homepage . Thank you Part 1-New Jersey’s OBD Inspection Test Components and Process NJ’s OBD Test – The Basics • Official testing of OBD eligible vehicles began in January 2004 • Allows the inspection workstation to read a vehicle’s OBD computer • Determines if there have been any malfunctions in the vehicle’semissions-related systems • Ensures that the OBD system itself is functioning properly • Captures additional data used for vehicle identification and fraud detection purposes OBD Testable Vehicles Gasoline • Model year 1996 and newer with a GVWR less than or equal to 8,500 pounds • Model year 2008 and newer with a GVWR between 8,501 and 14,000 pounds Diesel • Model year 1997 and newer with a GVWR less than or equal to 8,500 pounds Other Fuel Types Compressed Natural Gas (CNG), Liquefied Natural Gas (LNG), and hybrids follow the GVWR and model year cutoffs of their gasoline counterparts for the purposes of determining OBD applicability OBD Test Components 1. Visual MIL Bulb Check 2. Visual MIL KOER Check 3. DLC Condition Check 4. Communications Check 5. Readiness Status Check 6. MIL Command Status 7. DTC Check for those vehicles with the MIL commanded on OBD Test Sequence-Steps 1 & 2 1. Visual MIL Bulb Check-Performed by briefly turning the motor vehicle ignition system to the KOEO position and visually verifying that the MIL illuminates . If it does not illuminate, the vehicle has failed. 2. Visual MIL KOER Check-Performed by starting the vehicle, and visually determining if the MIL is on or off. If the MIL illuminates or flashes continuously while the engine is running, it is considered on . If the MIL is on, the vehicle has failed. OBD Test Sequence – Step 3 3. DLC Condition Check- If the DLC is damaged, missing, or obstructed, the motor vehicle has failed and the OBD test will end. If the DLC is present and accessible, the inspection workstation is connected to the DLC with the motor vehicle’s engine turned off. For the remainder of the OBD test, the motor vehicle is then started and left running (KOER) to allow the inspection workstation to attempt to communicate with the motor vehicle’s OBD system . OBD Test Sequence – Step 4 4. Communications Check- If the inspection workstation successfully communicates with the motor vehicle OBD system, it will then retrieve all of the required data from the OBD system . If the inspection workstation cannot successfully communicate with the motor vehicle’s OBD system after 4 attempts, the motor vehicle has failed the OBD test. OBD Test Sequence – Step 5 5. Readiness Status Check- If the inspection workstation determines that the vehicle’s OBD system does not indicate that the required number of supported readiness monitors have been set, the motor vehicle is deemed “not ready” for an OBD inspection and has failed the OBD inspection . The details for the number of required readiness monitors for each vehicle type is discussed in detail in the readiness criteria section of this module.

FAQs

What does the NJ OBD inspection test verify about the vehicle?

It confirms that the inspection workstation can read the vehicle’s OBD computer, checks for malfunctions in emissions-related systems, and ensures the OBD system itself is functioning properly. It also captures data for vehicle identification and fraud detection.

Which vehicles are eligible for NJ OBD testing based on model year and GVWR?

Gasoline: 1996+ with GVWR ≤ 8,500 lb, and 2008+ with GVWR 8,501–14,000 lb. Diesel: 1997+ with GVWR ≤ 8,500 lb. CNG/LNG and hybrids use the same GVWR and model-year cutoffs as their gasoline counterparts for OBD applicability.

What happens if the DLC condition fails or communications cannot be completed?

If the DLC is damaged, missing, or obstructed, the vehicle fails and the OBD test ends. If the inspection workstation cannot successfully communicate with the OBD system after four attempts, the vehicle fails the OBD test.

Oct 23, 2026

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