Knock Sensor Operation

Explains the Knock Sensor Operation and Testing. The Knock sensor is a actual microphone screwed into the engine block. It is tuned to listen to the exact frequency of an engine knock, which is a high frequency ping. A failing knock sensor will cause all sorts of problems to engine operation, such as skewed timing controls, loss of performance and power and ever the system going to linp-in mode. Learn how it works and how to test this incredible component. (note: We allow all schools and training institutions to use our software free of charge, so long as it is not sold to others. You're encouraged to download our free automotive simulation software for more information.

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[carveriscool]

I got a check engine light in my 1997 Subaru Impreza. It's a knock sensor code. There is a HUGE difference in acceleration when the check engine light (for the knock sensor) is on than when it's off.

[ADPTraining]

@carveriscool Yes, the knocking engine or perceived knock (assuming the sensor is giving an erroneous faulty reading) makes the ECM retard ignition timing. Try and disconnect the sensor and see what happens. THis may not solve your issue. Some systems sense a disconnected sensor and put out a code and retard timing. Good luck.

[FernterPix]

When the mechanic had it hooked up to the dang computer and got it to do it's stuttering,it gave the Knock Sensor code as the problem. What could cause the false/misleading reading?

[ADPTraining]

@FernterPix OK, first I can tell you that Nissan Knock sensors are always faulty after 50K miles or so. No biggie, that's not your issue. You have a misfire, either ignition, injector or valve problems (not likely). The knock on your vehicle is in the cylinder valley, under the intake. It is hard to get to and expensive to replace. Before you replace the knock get a proper diagnosis. Look in the areas mentioned. Post back when you get it fixed or done please, just to help others. THanks...

[FernterPix]

Would the Knock sensor make an engine hesitate while accelerating at a given speed? While cruising along around 50 mph and then giving it gas,the Xterra will "stutter" during acceleration.Once I'm passed a certain speed it seems to go away and is more evident during colder weather.

[ADPTraining]

@FernterPix Hello, well in your case the answer is no. On Nissans the knock sensor has an effect on timing, but not enough to cause hesitation. On other makes it is possible. It sounds like an ignition problem. Do a power brake test. Set parking brake on, step on brakes hard, set trans in drive and goose the accel pedal for up to 5 seconds (not longer). If hesitation is detected then suspect ignition problem. Post abck with more...

[shades2]

@carveriscool Cool. Did it fix the prob?

[carveriscool]

@shades2 I already ordered a new knock sensor a couple weeks ago.

[shades2]

@carveriscool Try changing your fuel to premium unleaded, add octane booster if necessary and see if that's the issue. Otherwise you might need to replace the sensor, or the engine have some other fault with timing etc. The ECU/ECM is trying to put the car into a limp-home mode I think to stop the knock/detonation damaging the engine.

[shades2]

On some cars, if knock is detected, the ECU/ECM will put the car into a limp-home mode to stop you revving it, creating detonation, and potentially causing major damage to one or more cylinders/pistons.

[zoharp55]

HTC evo vs iphone guy???

[StinkyTaco]

I didn't know stephen hawking was a mechanic...