4 Symptoms of a Bad Knock Sensor
Of course, when you’re rumbling down a long country road, you have no idea what’s going on in the engine bay. That’s because everything is so quiet these days.
But maybe your check engine light has come on when it wasn’t there before, or you’re hearing a strange knocking noise when accelerating. Maybe your mileage has dropped dramatically, or maybe something just isn’t right. There are a few possible causes for this problem, but it could be due to a faulty knock sensor.
What is a knock sensor? A knock sensor is a small round device found in the engine block or intake manifold of most internal combustion engines. The bottom of the sensor is bolted to the actual engine block or intake manifold, and the top of the sensor consists of a silicon ring, a piezoelectric crystal, and an electrode.
Your car’s computer constantly monitors and detects any noises that are made in the engine bay. This is important because there are normal and abnormal sounds. The latter indicates a problem in the engine compartment, and an engine code will appear on the dashboard.
Another type of knock sensor is the ion sensor. This method basically runs a current between the spark plugs and detects any type of current difference that might indicate an abnormality in the knock response.
What does a knock sensor do? This is a general explanation of how the sensor communicates with the car’s driver, but what exactly does the knock sensor do?
It basically lets you know if there’s a misfire or unusual combustion that doesn’t match up with other engine sounds. In most cases, this will turn on the check engine light, but if it doesn’t and your car still sounds a bit off, have a trusted mechanic take a look.
Where is the knock sensor? Knock sensors are often located directly on the outside of the engine block, but they may also be hidden under the intake manifold. The exact location of the sensor may vary from vehicle to vehicle, so we recommend consulting your model-specific repair manual.
Symptoms of a faulty knock sensor
1) Uncomfortable acceleration
One sign that your knock sensor is failing is if your car feels unnatural when accelerating or shifting into a higher gear than normal.
To test this, bring your car up to operating temperature. The next time you step on the accelerator, pay attention to how quickly the tachometer moves through the RPM range (revolutions per minute).
If you notice any wobbling when accelerating and it’s not running as smoothly as it used to, the knock sensor may be the culprit.
2) Low fuel economy
Another symptom that indicates a bad knock sensor is if your fuel economy suddenly becomes very high. You obviously keep careful records of your fuel economy data every time you fill up your tank (of course you do!), so you would notice within microseconds if your fuel economy starts to drop. Well, not really, but you get what I mean.
This is because your car’s computer detects the sensor failure and makes your engine less efficient by altering the ignition timing.
3) Check engine light
This is probably the easiest thing to notice. If your knock sensor is failing, the only thing you’ll see is the check engine light. On most cars, the light will stay on, but if it flashes, consult your manual to see what it means for your car. Then take your car to your preferred, trusted mechanic. DTC P0325, DTC P0326, DTC P0327, DTC P0328, and DTC P0332 are common trouble codes for a faulty knock sensor.
4) Retarded Timing
The last symptom of a bad knock sensor is the coolest in my opinion, and I really like it. If the knock sensor is bad, your car will effectively retard timing enough to not do any further damage, but enough to warrant a trip to the mechanic. Another interesting thing is that if you have an EcoBoost engine, a high compression engine like Mazda’s Skyactiv technology, or a flex-fuel engine, you will feel the effect more strongly if you have a faulty knock sensor.
