What does it mean?
OBD II fault code P02E9 is a generic code that is defined as “Diesel Intake Air Flow Position Sensor Circuit High”, or sometimes, and depending on the manufacturer, as “Intake Air Flap Control Actuator Position Sensor – Circuit High”. Both definitions have the same basic meaning, which is that the PCM (Powertrain Control Module) sets code P02E9 when it detects an abnormally high voltage in the control circuit of the Intake Air Flow Position Sensor on diesel engines that use these devices.
Note however that the code setting parameters and conditions vary between manufacturers, with “high” voltages ranging from 4.75 volts on some applications, to as high as 4.95 volts on others, which voltages must be present for periods ranging from three to five consecutive seconds before the code is set, depending on the application.
Intake-air flow control mechanisms are a relatively recent development on modern diesel engines, and the main function of these devices is to restrict the intake airflow in some situations to increase the effectiveness of the EGR (Exhaust Gas Recirculation) system, and by extension, the effect that introducing exhaust gas into the combustion chamber has on the reduction of harmful diesel exhaust emissions like nitric oxide and nitrogen dioxide, collectively known as NOx.
While EGR systems have been in use for decades, the technology can no longer satisfy the requirements of ever-more stringent emission control regulations. To comply with new regulations, manufacturers have introduced ways and means to increase the effectiveness of their EGR systems, one of which is to create a vacuum in the intake manifolds of their diesel engines.
It must be borne in mind at this point that diesel engines are not throttled like gasoline engines on the one hand, and that unlike gasoline engines, the air/fuel mixture on diesel engines can vary from a about 15 parts of air to one part of fuel, to as many as 60 parts of air to one part of fuel in some situations, on the other.
Moreover, since the power output of diesel engines is determined by the amount of fuel injected (as well as when the fuel is injected relative to the pistons’ position in their upward travel), as opposed to the amount of “fuel enrich-able” air that is available in the inlet manifold of a gasoline engine, there is always an excess of air in the inlet manifold of a diesel engine.
Put in another way, a diesel engine simply takes the amount of air it needs to combust the diesel fuel being injected at any given moment from the intake manifold, since there is no need to balance the volume of available intake air with the volume of fuel being injected into each cylinder. However, in some situations, this situation causes the formation of NOx when the combustion temperature approaches, or reaches 2 700°F (1 500°C).
By introducing exhaust gas into the cylinder via the EGR system, the combustion temperature can be kept below the level where NOx forms, but in older diesel engines, poor atomization of the fuel coupled with poor mixing of the intake air and partially atomized fuel reduce the quenching effect of the introduced exhaust gas.
To overcome these shortcomings, manufacturers have increased injection pressures to around 1 500 bar (21 755 PSI) to improve atomization, which is further improved by increasing the number of injection events to up to six during each injection cycle. However, to increase the rate at which intake air enters the combustion chamber in order to improve the mixing of the air/fuel mixture, manufacturers have introduced adjustable restrictions in the intake manifold.
While these restrictions resemble throttle bodies on gasoline engines in that that they consist of a moveable plate that looks like a conventional throttle plate, their sole function is to restrict the volume of air that flows into the manifold when it is partially closed. The effect of the restriction is to increase the speed at which the air flows through the manifold, which in tu