Circuit Description
The following applies to the intake airflow system performance diagnostic that is used in this supercharged engine:
- When referring to the supercharger intake manifold models, the plenum volume between the throttle body and the supercharger is considered to be the intake manifold.
- When referring to engine pumping, the supercharger and the intercooler plenum are considered to be part of the engine.
- The manifold absolute pressure (MAP) estimates are used in the engine air flow estimates. Air flow into the intake system must be the same as the air flow out of the intake system, the Intake Air Flow Rationality Diagnostics (IFRD) calculates air flowing out of the engine based on MAP estimates, volumetric efficiency, and RPM.
The engine control module (ECM) uses the following information to calculate an expected airflow rate:
- The throttle position (TP)
- The barometric pressure (BARO)
- The manifold absolute pressure (MAP)
- The intake air temperature (IAT)
- The supercharger inlet absolute pressure (SCIAP)
- The intake air temperature (IAT) sensor 2
- The engine RPM
The intake airflow system performance diagnostic provides the within-range rationality check for the mass air flow (MAF), supercharger inlet absolute pressure (SCIAP), MAP, by-pass valve stuck, and the throttle position (TP) sensors. This is an explicit model-based diagnostic containing separate models for the intake system.
The estimates of MAF, SCIAP, MAP, and TP that are obtained from this system of models and calculations are then compared to the actual measured values from the MAF, SCIAP, MAP, and TP sensors and to each other to determine the appropriate DTC to fail.