On 2003 VW 1.8t GTI MAF sensor there is a place for a resistor including diagram on the side but nothing is there. Check engine light is on. Is this only for some applications or is mine missing?

Answer 1

On normally aspirated cars, the MAF sensor contains both the plate resistor that serves to detect mass flow rate of air, as well as the temperature sensing bead resistor (thermistor) you make mention of that serves to detect intake air temperature.

The intake air temperature sensor is located at the intake manifold for 1.8Ts, both Audi and VW, not on the MAF. On these cars, the MAF only has the plate sensors that detect mass flow.

The reason behind this is that in normally aspirated cars, the temperature of air passing the MAF is approximately equal to the temperature of air entering the combustion chamber. In Turbocharged cars, the compression of air in the turbo raises the temperature of air, then the intercooler reduces the temperature thereafter. Thus the temperature of air passing the MAF could vary greatly from actual temperature of air entering the combustion chamber.

The ECU must obtain a correct temperature value for air entering the combustion chamber to provide correct fuelling, and to avoid a lean or rich combustion.

To ensure that the ECU gets correct values for temperature of air entering the combustion chamber, the thermistor is located after the turbo and intercooler on turbocharged cars.

On your 2003 VW 1.8t GTI, you can find it on the back of the intake manifold to the right side of the throttle body, opposite the fuel rail.