NOx Aftertreatment Monitor Diesel vehicles are now required to reduce NOx even further. A special catalytic converter is used to accomplish the NOx reductions. The catalytic converter is treated with a special washcoat containing zeolites. The zeolite acts as a molecular “sponge” to trap the NO and NO2 molecules in the exhaust stream. In some implementations, injection of a reactant before the aftertreatment purges it. NO2 in particular is unstable, and will join with hydrocarbons to produce H2O and N2. The NOx Aftertreatment Monitor monitors the function of the NOx … Read More
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Boost Pressure System Monitor The boost pressure system is used on diesel engines to increase the pressure produced inside the intake manifold to a level greater than atmospheric pressure. The pressure increase helps to ensure compete combustion of the air-fuel mixture. The Boost Pressure System Monitor checks for component integrity and system operation, and tests for faults in the system. The computer runs this Monitor once per trip. The Boost Pressure System Monitor is a “Two-Trip” Monitor. If a fault is found on the first trip, the computer temporarily saves … Read More
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Exhaust Gas Sensor Monitor Used only on diesel engines, the exhaust gas sensor is used to determine the content of the exhaust stream. The computer checks for component integrity, system operation, and tests for faults in the system, as well as feedback faults that may affect other emission control systems. The Exhaust Gas Sensor Monitor is a “Two-Trip” Monitor. If a fault is found on the first trip, the computer temporarily saves the fault in its memory as a Pending Code. The computer does not command the MIL on at … Read More
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Particulate Matter  Filter Monitor — PM Monitor Used only on diesel engine the particulate matter (PM) filter removes particulate matter from the exhaust stream by filtration. The filter has a honeycomb structure similar to a catalyst substrate, but with the channels blocked at alternate ends. This forces the exhaust gas to flow through the walls between the channels, filtering the particulate matter out. The filters are self-cleaning by periodic modification of the exhaust gas concentration in order to burn off the trapped particles (oxidizing the particles to form CO2 and … Read More
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Comprehensive Component Monitor —CCM I/M Monitor The CCM continuously checks all inputs and outputs from all the sensors, actuators, switches and other devices that provide a signal to the computer. The comprehensive component monitor is always looking for a short, open, out of range value, functionality and “rationality.” What is rationality in a monitor? The simple answer is this; the computer is checking to see if the sensor’s value makes sense. The computer compares all other inputs and against information in the computer’s memory to see if the values are … Read More
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Misfire Monitor — Readiness Monitor for Misfires In short, the I/M Readiness Misfire Monitor is a continuous monitor that is always checking for r engine misfires. How misfires are detected The misfire monitor detects misfires in two ways. In vehicles equipped with smart ignition coils, the COP coil itself reports a misfire to the ECM. In other vehicles, the misfire monitor tracks the crankshaft position sensor to detect a slowdown in crankshaft rotation that indicates a cylinder didn’t fire or “contribute” power. Engine RPM isn’t constant; instead it’s a series … Read More
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Fuel System Monitor — How it works The Fuel System Monitor is actually more of a Fuel System Correction program. The ECM is constantly monitoring how well it did in calculating fuel-to-air ratios. When it must make an adjustment from factory programming; either by adding fuel or subtracting fuel, it enters those corrections into either short term fuel corrections or long term fuel corrections. Those corrections are referred to as Fuel Trim What is Fuel Trim? Fuel Trim is a set of positive and negative adjustments to factory air/fuel programming … Read More
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Oxygen Sensor Monitor In simple terms, the Oxygen Sensor’s only job is to monitor how much oxygen is in the vehicle’s exhaust stream. The ECM uses this information to determine how good of a job it did in calculating the air/fuel ratio based on the current driving conditions (outside air temperature, engine temperature, accelerator pedal position, air mass, etc.). Based on the results, the ECM makes changes to future air/fuel calculations. How oxygen sensors work Carmakers use various types of oxygen sensors, with the most recent designs called air/fuel ratio … Read More
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Oxygen Sensor Heater Monitor The Oxygen Sensor Heater Monitor’s job is to constantly monitor the operation of the oxygen sensor’s heater. There are two modes of operation on a computer-controlled vehicle: “open-loop” and “closed-loop.” The vehicle operates in open-loop when the engine is cold. During open loop, the ECM calculates fuel based on outside air temperature and engine coolant temperature sensor readings only, ignoring data from the oxygen sensors. However, once the oxygen sensors’ heaters bring the sensor up to 600°F operating temperature, the ECM switches to closed loop operation … Read More
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