How Do You Know When a Knock Sensor Is Bad?

Car Culture/Car Culture @ Collection/Getty Images

The most common symptoms of a faulty knock sensor are engine noises, flashing dashboard or “Check engine” lights and diminished fuel economy. These symptoms are most common when the vehicle is travelling at highway speeds or carrying a heavy load. To properly assess the condition of the knock sensor, compare engine performance to its factory specifications found in the vehicle’s manual.

Flashing or activated warning lights are the most common indication of a bad knock sensor. A faulty knock sensor pairs activated or flashing warning lights with strange engine noises, which are the most common symptoms associated with faulty knock sensors.

Common engine noises associated with faulty knock sensors include sputtering, knocking and pounding sounds. These noises stem from pre-ignition, which results from fuel and air igniting inside the cylinders instead of burning evenly throughout the engine.

Faulty knock sensors also decrease fuel economy. Fuel efficiency decreases with faulty knock sensors because of an improper mixture of fuel and air. The engine cannot combust properly, which leads to higher emissions and reduced fuel economy.

A faulty knock sensor miscalculates the fuel to air ratio. When this ratio is not properly determined, the vehicle cannot accelerate nor use fuel efficiently. Faulty knock sensors disrupt communication between the engine and the vehicle’s computer. This disruption diminishes vehicle performance through a misallocation of fuel delivered to the engine.