To retrieve the OBD II code, the self-diagnosis system needs a special SCAN tool, hence if unavailable, the code should be retrieved by a dealer or a qualified retrial facility. For the NO START condition home mechanics can carry out several checks and adjusted, however, for intermittent problems to the drive ability a SCAN tool should be used for monitoring the operation of the sensor. Coolant and intake air temperature sensors for example, are a type of thermistor sensors which are variable resistors that translates temperature variation in to voltage signals with tendency of offering higher resistance when the temperature is low and a low resistance when the temperature is high. To test, first take a multi-meter and check the resistance of which would be low and the reference voltage which would lie around 5.0 volts. Variety sensors similar to throttle position include potentiometer sensors that control resistance based on the position and the resistance can be tested by measuring the change in resistance in addition to the voltage signal change while in operation. Specific checks on magnetic reluctance sensors, those used for crankshaft and vehicle speed sensing, include the resistance tests and voltages' observations using an AC voltmeter. Controlled by the ECM, oxygen sensors measure exhaust oxygen levels, whose voltage output helps the engine adjust the air/fuel ratio; during the test, the signals in millivolts and heater must be inspected. Intake air flow sensors quantify air going into the engine, and due to differences in make and model, have varying designs; they can be tested for voltage changes or output using a SCAN tool. Most modern cars incorporate Knock sensors which help in identifying its vibrations that cause spark knock, while there is the Neutral Start switch that helps in sending transmission position to the ECM. It is therefore in charge of compressor engagement for the air conditioning system and checks on the pressure in the power steering during idling. Lastly, the vapor pressure sensor is used to detect fuel tank pressure during emission tests and replacing these sensors or their related circuitries should be done by professional mechanic.