What does it mean?
To get more power out of a set engine displacement, engine designers have come up with a number of ways, forced induction being one of them. In the intake, a compressor forces more air into the cylinders than they could normally suck in on their own. Turbochargers use exhaust gas flow to spin up the compressor, while superchargers use a belt-driven compressor, with similar results. Some forced-induction engines may use more than one turbocharger or a combination of turbocharger and supercharger.
Forcing more air into the cylinder, which is why it’s called “forced induction,” results in more oxygen for combustion, for which the engine control module (ECM) injects more fuel, resulting in more power. Overall, the addition of forced induction to an engine can generate upwards of 40% more power than a naturally-aspirated engine of the same displacement.
One particular turbocharged 1.8 ℓ engine may produce 130 hp, while a turbocharged version of the same engine could produce up to 220 hp, a 70% increase in maximum power. As with non-forced-induction engines, the ECM on a forced-induction uses a number of sensor readings to meter fuel injection and modulate ignition timing and variable valve timing, such as air flow and air temperature.
Additionally, charged engines may have a few dedicated sensors, such as those measuring boost pressure and intake air temperature (IAT), which the ECM uses to tune fuel trim. If intake air temperature is too high, this could result in increased cylinder temperatures and excessive NO x (nitrogen oxides) emissions, so the ECM can reduce boost pressure if required. Forced-induction engines have two IAT sensors.
Usually, IAT or IAT1 refer to the sensor measuring air temperature coming into the mass air flow (MAF) meter. Because air temperature increases under compression, from the turbocharger or supercharger, sensor IAT2 is used to measure air temperature after just after the compressor.
If the ECM detects a problem with IAT2, such as temperature or voltage out of specification, it will illuminate the malfunction indicator lamp (MIL) and store a diagnostic trouble code (DTC), P0098 Intake Air Temperature Sensor 2 Circuit High Input, in memory.