Circuit Description
The mass air flow (MAF) sensor is integrated with the multifunction intake air sensor. The MAF sensor is an air flow meter that measures the amount of air in the sensor bore. The engine control module (ECM) 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 scan tool Induction System Leak Indication parameter is calculated by dividing the mass air flow sensor signal reading, by the estimated air flow.
The estimated air flow is based on the following signal readings:
- Engine speed
- Manifold absolute pressure (MAP)
- Intake manifold temperature (IAT 3) sensor
When the EGR valve is closed, the ideal Induction System Leak Indication parameter is 1.0:1; the normal range is between 0.75:1 and 1.25:1.
A scan tool Induction System Leak Indication parameter greater than 1.25:1, when the EGR valve is commanded closed, may indicate:
- A leak after the turbocharger
- An inaccurate boost pressure sensor
- An inaccurate IAT sensor 3
- A skewed MAF sensor
A scan tool Induction System Leak Indication parameter less than 0.80:1, when the EGR valve is commanded closed, may indicate:
- A leak before the turbocharger
- An inaccurate boost pressure sensor
- An inaccurate IAT sensor 3
- A skewed MAF sensor
- A leaking EGR valve, when it is commanded closed
- A leaking positive crankcase valve (PCV) system
The ECM applies 5 V to the MAF sensor on the MAF sensor signal circuit. The sensor uses the voltage to produce a variable frequency signal based on the inlet air flow through the sensor bore. The signal varies with engine load and is displayed by the scan tool as Hertz (Hz) and grams per second (g/s). Ignition voltage and ground circuits are also supplied to the multifunction intake air sensor internal circuits for the sensors listed below.
The multifunction intake air sensor houses the following:
- Intake Air Temperature (IAT) sensor 1
- IAT sensor 2
- Humidity sensor
- MAF sensor
- Turbocharger inlet air pressure (TCIAP) sensor - BARO 2