Monitors
Monitors are groups of sensors that conduct test exercises for vehicle. These monitor tests ultimately turn the Malfunction Indicator Light (MIL), also known as check engine light, on or off. Monitors set Diagnostic Trouble Codes (DTCs) and automatically clears them. Monitors are vital for vehicle diagnostics and is one of the core modules for OBD-II compliant vehicles.
Vehicle Monitors
A vehicle’s monitors run when the vehicle is in operation, interrogate all sensors within their jurisdiction, coordinates the results and analyses them for completeness.
Monitors run only when they have fulfilled their enabling criteria. Enabling criteria are requirements specific to each monitor. Once a monitor has achieved its enabling criteria, the monitor will run tests to check for synchronism and responsiveness between specific sensors in the vehicle. It is important to remember that although all cars have similar monitors, manufacturers don't have to select the same test strategies and sensors for the individual monitors to run.
Continuous and Non-continuous Monitors
There are several types of monitors a car computer can run. The different types depend on the manufacturer and whether the vehicle is a spark ignition (petrol/regular gas) or compression ignition (diesel gas) engine. Although spark ignition and compression ignition do have common monitors, it’s important to remember these are different systems that run at different temperatures and pressures. The sensor readings can vary significantly, so the troubleshooting approach should be taken with precaution.
Some monitors can run continuously, and some run only once when the enabling criteria are satisfied. Be sure to read up on the individual monitors themselves.
Continuous Monitors
When the enabling criteria for these kinds of monitors are met for the first time, the monitors begin to run and continuously review the monitoring systems for a component, electrical or logical failure.
There are three continuous monitors: Comprehensive Component Monitor, Misfire Detection Monitor, and Fuel System Monitor. These monitors hold the responsibility of flagging any major issues that may cause direct problems to the catalytic converter (please refer the descriptions for these monitors more information)."
Non-Continuous Monitors
For these kinds of monitors, they perform and complete their testing once per trip only when the enabling criteria are met and are tricky and more difficult to understand. The NON-CONTINUOUS monitors are different for spark ignition (gasoline engines) and compression ignition (diesel engines) vehicles.
Monitor Types
Spark Ignition Monitors
A few of these non-continuous monitors together with the continuous once will appear on the monitor screen of the check engine app if your vehicle uses gas/petrol
Oxygen Sensor Monitor
Oxygen Sensor Heater Monitor
Secondary Air System Monitor
Evaporative System Monitor
A/C Refrigerant Monitor
Catalyst Monitor
Heated Catalyst Monitor
Exhaust Gas Recirculation (EGR) Monitor and/or Variable Valve Timing (VVT) Monitor
Compression ignition (diesel) Non-continuous monitors include:
A few of these non-continuous monitors together with the continuous once will appear on the monitor screen of the check engine app if your vehicle uses diesel. The number and combination is determined by the type of engine and the vehicle manufacture.
NOx/SCR Monitor
NMHC Catalyst Monitor
Boost Pressure Monitor
Exhaust Gas Sensor Monitor
PM Filter Monitor
Exhaust Gas Recirculation (EGR) Monitor and/or Variable Valve Timing (VVT) Monitor
Monitor Statuses
There are 2 statuses of monitors. These can be changed on the check engine app by clicking on the drop down box under the title bar.
Status since DTC cleared
The states of these monitors as at the last time they successfully completed a monitor run after the diagnostic information was cleared.
Status this drive cycle
The states of these monitors only for the current drive cycle, meaning the status since the last time the engine was turned on.