Knock sensor/Jetta 2V, Ford/OE NO.030905377C, 1205185, YM2112A699BA

Automobile engines are complicated machines. They require a multitude of belts, fluids, moving parts and chain reactions all occurring in the correct timing and rhythm for your car to run efficiently. If one device fails or if a part doesn't move at the precise time it needs to, the car may not run correctly or the engine may be damaged. One of the components that is vital to your car running properly is the knock sensor.

Function

1. The knock sensor is a listening device located inside the engine near the intake manifold or the pistons that is designed to detect pressure inside the engine. The vibrations that it records as a result of this pressure are converted into voltage and sent to the car's engine control unit (ECU). This is to prevent detonation in the engine when the fuel/air mixture explodes too quickly and causes engine knock or "pinging." The ECU takes the information provided by the knock sensor and adjusts the ignition timing to the engine.

Components

1. The knock sensor is made of a piezoelectric element that has a coil around it. A wire connects the sensor directly to the ECU. When the element vibrates, it sends electric current through the wire to the ECU, which then interprets the reading. There is generally one knock sensor for every four cylinders in the engine.

Benefits

1. "Pinging" or engine knock happens when there is an early explosion in the combustion chamber of the engine. The flame collides with the piston which is still rising (or the spinning rotor in the case of a rotary engine) which results in engine vibration and engine knock. In minor cases, this results in a decrease in engine power. If it gets severe, major engine damage could result which would require up to thousands of dollars to repair. The knock sensor is the key instrument that prevents this from happening and keeps the timing of the engine running smoothly and safely. In some models, the knock sensor serves a dual purpose of also increasing the ignition timing to the level just below engine knock to achieve optimal power and performance.

Symptoms of Failure

1. Symptoms Include:

   • SES Light
   • Hesitation
   • Bucking at high RPMS
   • Audible missing or pinging
   • Surging

Replacement

1. Depending on the make and model of your car, replacing a knock sensor can be very expensive. It is cheaper to replace it yourself but is very time-consuming and only recommended if you have a knowledge about automobiles. Some models have the knock sensor stored inside the engine block, in which case the radiator coolant would need to be drained. The sensor must also be torqued to exact specifications or it will be too sensitive to vibration and harm engine performance or not work at all. Refer to your owner's manual for the specifics on your engine