What Happens When a Knock Sensor Fails?
2 Answers
When the knock sensor is damaged, the resulting symptoms include the inability to detect engine knock signals, failure to automatically retard ignition timing, engine knocking, insufficient engine power, and audible piston slap. The specific details are as follows: 1. During engine operation, factors such as excessive ignition timing advance (ignition advance angle), engine load, temperature, and fuel quality can cause engine knocking. When knocking occurs, because the combustion of gases happens before the piston reaches top dead center, mild cases produce noise and reduce engine power, while severe cases can damage the engine's mechanical components. To prevent knocking, the knock sensor is an essential component that adjusts ignition timing through the electronic control system. 2. The knock sensor is mounted on the engine block, typically between cylinders for a four-cylinder engine: either between cylinders 2 and 3, or one between cylinders 1 and 2 and another between cylinders 3 and 4. Its function is to measure engine vibration. When knocking occurs, the knock sensor converts the engine's mechanical vibration into a signal voltage and sends it to the engine control unit (ECU). The ECU then calculates and adjusts the ignition advance angle based on pre-stored ignition and other data to optimize ignition timing and prevent knocking.
The most obvious symptom of a faulty knock sensor is reduced engine power, sluggish response when accelerating, and occasional abnormal engine noises like metallic knocking sounds. This happens because the sensor fails to detect knocking, preventing the engine computer from automatically adjusting valve timing and ignition timing. Increased knocking can cause engine overheating and even damage pistons or valves. From my repair experience, this fault also increases fuel consumption due to incomplete combustion. If not repaired promptly, it may lead to more severe engine problems with costly repairs. Therefore, when the check engine light comes on or abnormal noises are heard, it's best to get it checked at a repair shop immediately to avoid roadside breakdowns. Paying attention to normal engine sounds during daily driving can help detect issues early.
