Mass Air Flow and Intake Air Temperature Sensor - (From 99MY)

Mass Air Flow (MAF) and Intake Air Temperature (IAT) Sensor - (From 99MY)






The MAF/IAT sensor is located at the RHS of the engine compartment, in the air intake duct between the air filter housing and the inlet manifold. The complete assembly forms part of the air intake tube, but the sensor itself is attached by two torx screws and can be removed from the intake tube if necessary.

The upper section of the intake tube containing the MAF/IAT sensor is embossed with an arrow indicating the direction of air flow, always ensure the unit is fitted in the correct orientation.


CAUTION: Take care handling the sensor unit, it should not be dropped or roughly handled, ensure that the unit remains free of contamination.


The sensor has a five pin connector which connects to the ECM via the engine harness. The connector has silver plated terminals for low current signals and corrosion protection. The harness is clipped to prevent vibration of the terminals.

MAF SENSOR
The Mass Air Flow sensor utilizes a "hot film" element contained in the air intake tube to monitor the mass flow of the air stream being drawn into the engine. The MAF sensor contains two sensing elements, one element is controlled at ambient temperature (e.g. 25° C (77° F), while the other is heated to 200° C (360° F) above the ambient temperature (e.g. 225°C (437 °F)).

When the intake air passes the heated element, it cools it down, so lowering the resistance of the hot film element. In order to maintain the same temperature, the circuit to the heated element has to supply more current. The change in current causes a corresponding change in potential difference to be detected in the monitoring circuit. This change is supplied to the ECM as a voltage between 0 and 5V, where it is processed by the ECM's internal mapping to interpret the data as a measure of the mass of air flow.

The measured air mass flow is used by the ECM to determine the fuel quantity to be injected in order to maintain the stoichiometric air:fuel mixture for optimum engine performance and low emissions.

The MAF sensor receives a power supply via the engine compartment fusebox, and a 5V reference signal from the ECM. The MAF sensor and the AT sensor share a common ground connection and each provide a separate signal input to the ECM.


CAUTION: Do not apply 12 V directly to the 5 V supply terminal, this will destroy the internal circuitry. The connector terminals are silver plated - avoid probing with multimeter test leads.


If the MAF sensor fails, the ECM implements a backup strategy which is based on throttle angle, air temperature and engine speed. A MAF sensor failure may result in the following symptoms being experienced:

- The engine rpm may relapse slightly during driving and then recover.
- Difficulty in starting and/or frequent stalling of engine.
- Poor throttle response
- Degraded engine performance.
- Emissions control and idle speed control inoperative.
- MAF sensor signal offset.

A MAF sensor failure is likely to occur for the following reasons:
- Sensor open circuit of voltage supply, signal or ground lines.
- Short circuit of signal line to vehicle supply or ground.
- Contaminated /damaged sensor element.
- Air leak after the MAF sensor.
- Inlet air restriction.
- Poor connection or resistance in wiring harness causing signal offset.

If the MAF sensor should fail, the following fault codes will be generated by the ECM diagnostics, which can be retrieved by Testbook:

- P0102 - (MAF signal less than the speed dependent minimum threshold).
- P0103 - (MAF signal greater than the speed dependent maximum threshold).

Intake-air density varies with temperature, the ECM needs to be aware of these changes so that corrective calculations can be incorporated into the ECM's fuelling and ignition timing strategies. The intake air temperature value is also used by the ECM as a reference when implementing compensation for an ECT failure.

IAT SENSOR
The intake air temperature sensor utilizes a thermistor with a negative temperature CO-efficient (as temperature rises, thermistor resistance decreases). The change in resistance causes a change in input voltage at the ECM. The ECM converts the voltage value it receives to provide an indication of the temperature of the inlet air.

If the IAT sensor fails, the ECM substitutes a default value for air temperature of 45° C (113° F). An IAT sensor failure may result in the following symptoms being experienced:
- Catalyst monitoring affected due to exhaust temperature model.
- Warm-up ignition angle affected.
- ISC speed adoption disabled
- ISC actuator blocked test disabled
- Fuelling adoptions disabled.

An IAT sensor failure is likely to occur for the following reasons:
- Sensor open circuit.
- Sensor signal line short circuit to vehicle 12V supply or ground.
- Damaged sensor element
- Bad connection or increased resistance in wiring harness.

If the IAT sensor should fail, the following fault codes will be generated by the ECM diagnostics, which can be retrieved by Testbook:

- P0112 - (air temperature signal is less than the minimum threshold - after a sufficient time (more than three minutes) for exhaust warm-up has been allowed).
- P0113 - (air temperature signal greater than the maximum threshold).