Circuit Description: Notes

IMPORTANT: The following applies to the intake air flow system performance diagnostic that is used in this supercharged engine:

When referring to the "intake manifold models", the plenum volume between the throttle body (TB) 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) sensor that resides in the engine intake manifold is used to adjust the engine air flow estimates to balance the air flow models.

The supercharger inlet absolute pressure (SCIAP) sensor measures the absolute pressure of the air just after the TB, thus just before the supercharger. The plenum volume between the TB and the supercharger is where this sensor is located, and for the purpose of this diagnostic, this area is considered to be the intake manifold. The diaphragm within the SCIAP sensor functions in the same manner as the barometric pressure (BARO) sensor. These sensors are not interchangeable.

The intake air flow system performance diagnostic provides the within-range rationality test for the mass air flow (MAF), the SCIAP, and the throttle position (TP) sensors. This is an explicit model-based diagnostic containing four separate models for the intake system.

The throttle model describes the flow through the throttle body and is used to estimate the MAF through the throttle body as a function of BARO, throttle position, intake air temperature (IAT), and estimated SCIAP.
The first intake manifold model describes the intake manifold and is used to estimate SCIAP as a function of the MAF into the intake manifold from the throttle body and the MAF out of the intake manifold caused by engine pumping. The flow into the intake manifold from the throttle uses the MAF estimate calculated from the throttle model.
The second intake manifold model is identical to the first intake manifold model except that the MAF sensor measurement is used instead of the throttle model estimate for the throttle air input.
A fourth model is created from the combination and additional calculations of the throttle model and the first intake manifold model.

The estimates of the MAF, the SCIAP, and the TP that are obtained from this system of models and calculations are then compared to the actual measured values from the MAF, the SCIAP, and the TP sensors and to each other to determine the appropriate DTC to fail. The following table illustrates the possible failure combinations and the resulting DTC or DTCs.

DTC P012B

Throttle Model	First Intake Manifold Model	Second Intake Manifold Model	Fourth Model	DTCs Passed	DTCs Failed
X	X	Pass	Pass	P0101 P0121 P012B P1101	None
Pass	Pass	Failed	Pass	P0101 P0121 P012B P012B P1101	None
Failed	Pass	Failed	Pass	P0121 P012B P1101	P0101
Pass	Failed	Failed	Pass	P0101 P0121 P1101	P012B
Failed	Failed	Failed	Pass	P0121 P1101	P0101 P012B
X	X	Pass	Failed	P0101 P012B P1101	P0121
Pass	Pass	Failed	Failed	P0101 P0121 P012B P1101	None
Failed	Pass	Failed	Failed	P0101 P0121 P012B	P1101
X	Failed	Failed	Failed	P0101 P0121 P012B	P1101

If the engine control module (ECM) detects that the actual measured air pressure from the SCIAP sensor is not within range of the calculated air pressure for the SCIAP sensor that is derived from the system of models, DTC P012B sets.