What are the symptoms of a faulty knock sensor?
3 Answers
Symptoms of a faulty knock sensor include: 1. Reduced engine power; 2. The engine produces knocking sounds; 3. Damage to engine pistons and cylinder block; 4. Inability to detect engine knock signals; 5. Failure to automatically retard ignition timing; 6. The engine warning light on the dashboard will illuminate. The knock sensor is installed in the middle of the engine block and is used to measure engine vibration. When engine knock occurs, it adjusts the ignition timing. The working principle of the knock sensor is: When vibration or knocking occurs, it generates a small voltage peak. The greater the knocking or vibration, the higher the voltage peak produced by the knock sensor. A certain high frequency indicates knock or engine knocking. Knock sensors are typically designed to measure frequencies in the range of 5 to 15 kHz. When the control unit receives these frequencies, the ECU adjusts the ignition timing to prevent further knocking.
When the knock sensor fails while driving, you'll hear a metallic 'clicking' sound from the engine, especially noticeable during acceleration or climbing hills. It sounds like little hammers randomly tapping inside the engine, and it gets really annoying over time. The power output will also drop – you press the accelerator but the car feels sluggish, normally you could overtake with a quick step on the gas, but now it feels slow and unresponsive. What's worse, fuel consumption shoots up, a full tank lasts just a few days, wasting money. If the check engine light stays on, it's basically the sensor sounding the alarm. This isn't a minor issue – prolonged knocking can damage internal engine components like pistons and valves, leading to expensive repairs. From my experience, don't ignore it. Get to a repair shop quickly for a computer diagnostic. Replacing the sensor usually solves the problem. During regular maintenance, also remind them to check the sensor connections – don't wait until it completely fails to take action.
When the knock sensor fails, the entire engine operation goes haywire. Its original job was to monitor the combustion process for abnormal vibrations and help the ECU adjust ignition timing. Now that it's out of commission, the ECU is essentially blind, unable to control ignition timing properly, leading to uneven air-fuel mixture and causing the engine to rattle and ping. This noise becomes especially harsh at higher RPMs, making it downright scary to drive. Power loss is also noticeable—acceleration feels sluggish, climbing hills becomes a struggle, and fuel efficiency plummets. What used to be 7-8 liters per 100 kilometers might now soar above 10 liters. The check engine light comes on, and a scanner will read codes like P0325. Even worse, prolonged operation with engine knock accelerates wear on cylinder walls and piston rings, potentially leading to a costly engine overhaul. Whenever I see cases like this, I always advise owners not to skimp—replace the sensor promptly, or the repair bill will really hurt.
