The mass air flow (MAF) sensor in your 1996 Hyundai Sonata measures the amount of air flowing through the air cleaner assembly and into the engine. Overtime, though, dirt sticking on internal wires, circuitry malfunctions and failed internal components may render the MAF inoperative. So, finding the real source of the problem is important to avoid unnecessary replacements and expensive repairs. The MAF sensor in your Sonata is relatively accessible and you can troubleshoot it at home with a minimum of equipment and tools.
Park your Sonata in a place with enough air ventilation. If you are inside your garage, open the door to the driveway. Start the engine and let idle for about 15 minutes so that it reaches operating temperature and then turn off the engine.2
Open the hood and locate the MAF sensor. You will find the sensor mounted in the air cleaner assembly, between the air box, which contains the air filter, and the throttle body, which is the gate to the intake manifold, on top of the engine. You will see a four-prong electrical connector protruding from the sensor.3
Inspect the wires visually in the harness connector leading to the sensor's connector, making sure they are in good condition and properly attached. Slightly pull on each of the four wires to make sure they are firmly attached.4
Back probe the MAF sensor signal output and ground wires with your 10 megohm digital multimeter. The red wire with a blue stripe is the signal wire. The green wire with the white stripe, or third wire from the signal wire, is your ground. Connect the red meter probe to the signal wire and the black probe to the ground wire.5
Set your meter to a low range on the Direct Voltage scale so that you can read up to 5 volts.6
Ask an assistant to start the engine and to keep it at idle. Read off the value on your digital meter display. It should be between 0.7 and 1.1 volts.7
Ask your assistant to rev up the engine up to 3000 rpm. Your meter display should read now between 1.3 and 2.0 volts. Turn off the engine. If the MAF sensor failed these tests, disconnect the ground (black) battery cable with a wrench and remove the sensor from the air cleaner assembly with a Phillips screwdriver without touching the mesh wires inside the sensor.8
Place the sensor on a workbench and spray the wire mesh with mass air flow sensor cleaner, following the instructions on the product label, and reinstall the sensor in the air cleaner assembly.9
Reconnect the ground (black) battery cable with a wrench and repeat steps 4 through 7. If your MAF sensor's readings are still out of specification, replace it.