Circuit/System Description: Notes

P0101

• The mass air flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The control module uses the MAF sensor signal to provide the correct fuel delivery for all engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle condition. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has the following circuits:
  • An ignition 1 voltage circuit
  • A ground circuit
• The control module applies a voltage to the sensor on the signal circuit. The sensor uses the voltage to produce a frequency based on the inlet air flow through the sensor bore. The frequency varies within a range of near 2,000 Hertz at idle to near 10,000 Hertz at maximum engine load. The control module uses the following sensor inputs to calculate a predicted MAF value:
  • The barometric pressure (BARO) at key ON
  • The manifold absolute pressure (MAP) sensor
  • The intake air temperature (IAT) sensor
  • The engine coolant temperature (ECT) sensor
  • The throttle position indicated angle
  • The engine speed (RPM)
• The control module compares the actual MAF sensor frequency signal to the predicted MAF value. This comparison will determine if the signal is stuck based on a lack of variation or is too low or too high for a given operating condition. If the control module detects the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value, DTC P0101 sets.

P1101

• The intake flow rationality diagnostic provides the within-range rationality check for the MAF, MAP and the throttle position (TP) sensors. This is an explicit model-based diagnostic containing 4 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, TP, IAT and estimated MAP.
  • The first intake manifold model describes the intake manifold and is used to estimate MAP as a function of the MAF into the manifold from the throttle body and the MAF out of the manifold caused by engine pumping. The flow into the manifold from the throttle uses the MAF estimate calculated from the above 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.
  • The fourth model is created from the combination and additional calculations of the throttle model and the first intake manifold model.
• The estimates of MAF and MAP obtained from this system of models and calculations are then compared to the actual measured values from the MAF, MAP 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.