OBD2 Monitors

Purpose

To help you understand the definitions of OBD2 monitors.

Introduction

To ensure the correct operation of the various emissions-related components and systems, a diagnostic program was developed and installed on the vehicle’s onboard computer. The program has several procedures and diagnostic strategies. Each procedure or diagnostic strategy is made to monitor the operation of, and run diagnostic tests on, a specific emissions-related component or system. These tests ensure the system is running correctly and is within the manufacturer’s specifications. On OBD2 systems, these procedures and diagnostic strategies are called 'Monitors'.

Currently, fifteen Monitors are supported by OBD2 systems. Additional monitors may be added because of Government regulations as the OBD2 system grows and matures. Not all vehicles support all fifteen Monitors. Additionally, some Monitors are supported by 'spark ignition' vehicles only, while others are supported by 'compression ignition' vehicles only.

Monitor operation is either 'Continuous' or 'Non-Continuous,' depending on the specific monitor.

Continuous Monitors

Three of these Monitors are designed to constantly monitor their associated components and/or systems for proper operation. Continuous Monitors run constantly when the engine is running.

Non-Continuous Monitors

The other twelve Monitors are 'non-continuous' Monitors. 'Non-continuous' Monitors perform and complete their testing once per trip.

Note: The following Monitors became standard beginning in 2010. The majority of vehicles produced before this time will not support these Monitors.

Additional Terminology and Acronyms

DLC = Data Link Connector (vehicle’s data port)
DTC = Diagnostic Trouble Codes
MIL = Malfunction Indicator Lamp (Check Engine Light)
OBD = On Board Diagnostics
OBD2 / OBD II = On Board Diagnostics, Second Generation
OEM = Original Equipment Manufacturer
TSBs = Technical Service Bulletins