Mass airflow sensors measure the amount of air by weight through changing voltages or frequencies and sends this information to the onboard computer. The computer uses this and other inputs to calculate the correct amount of fuel delivered. Symptoms of failure include poor starting, engine surging, engine stalling, a check engine light, and no-start conditions. Sensors are non-serviceable, replace sensors that are non-functional. Walker Products began supplying the fuel system needs of the automotive industry in 1946. Today Walker is one of the largest, privately owned manufacturers of fuel system components and engine sensors, and has served the needs of the worldwide automotive aftermarket. We are committed to supplying products manufactured to meet or exceed OEM standards and specifications. This effort is backed by our own manufacturing, product management and engineering staff to ensure it is maintained and accurate in the production of quality parts, vehicle applications, instruction sheets and technical support. Our products include Carburetor and Fuel Injection Repair Kits, Oxygen Sensors and other Engine Management products such as Throttle Position Sensors, Cam and Crankshaft Sensors, Fuel Injectors, Spark Plug Wires and Gaskets. As an ISO 9001: 2008/TS16949 certified company, we are committed to supplying the highest quality products. Vehicle Fitment: 1999-2004 Volvo S40 1. 9L, Volvo S80 2. 8L, Volvo V40 1. 9L