Let me start by first off I replaced plugs, wires, and washed the motor. I then took about a 240 mile trip and got a engine light. It turned out to be the #2 knock sensor. It was rusted and had 195k on it. I replaced it and it lasted a week. So I replaced it and also replaced the harness. Now two weeks later its got the code for the same thing and its running like a dog again. Btw after it throws a code for about 2 days it starts running rough. It even has a miss at idle. You can watch the motor have a jerk type motion at idle and you can feel it at highway speeds. I am getting the code for low output knock sensor 2{again}. Please help

 

It will either be a bad sensor which is doubtful. I'm betting on the wire is broke or breaking inside the insulation in the area between the valve cover and the underhood power distribution center. I'd start by replacing the wire from the pcm to the knock sensor connector for both knock sensors.

Wires breaking in the area is a very common problem when they start getting a ton of miles and age on them.

 

Did you replace both sensors? What brand did you use?

 

You torquing it down to only 15ft lbs.?

 

The sensors are very delicate. I recommend getting an OEM one from the dealer. It must also be torqued to the correct value so you don't damage the gizmo in side.

I bought one through the auto parts store and it had all the same markings as an OEM. I thought I did good saving $10 and not having to go to the dealer. Well just past the 90 day warranty mark it went out again... at least through the dealer you get a 1 year warranty. I ended up acquiring a used original one from another motor and figured what the hell it was free... It has been in there ever since and that was 3-4 years ago...

 

Actually, the torque is not important as far as damaging the piezo inside (unlikely anyway). The torque setting is EXTREMELY important though as a ft/lb more or less causes the sensor to be quieter or louder. The tighter you make it, the louder it gets. The ECM uses the signal level to determine what amount of "bang" at what time is good for the engine. Too tight and you pick up mechanical noise, too loose and you don't have pulse from cylinders firing.

Therefore, just putting it on with a socket wrench is going to make it wrong immediately and any function out of an improperly torqued sensor is dumb luck.

Also, when you are replacing knock sensors, you should be replacing them in pairs. MATCHING pairs.

Torque the sensor to 20 N.m (15 lb ft). YOU NEED A TORQUE WRENCH!

 

Thanks for Clarifying that!!!

I was taught differently in regards to it becoming damaged from over torquing. However i am always interested in learning something new.

In my case I did both sensors, the harness, and new intake gaskets following the latest TSB info. Unfortunately the rear failed just passed the 90 day mark and the store was un-willing to stand behind it. Had it not come at a time were I was strapped for cash I would have bought Everything from the dealer not just the harness. I may have saved nearly $50 on parts at my cost but the aggravation was not worth the hassle. Luckily the Free used one worked out well. It was in good shape and may have been a replacement on the other motor.

 

I should add, the only way I know of to break a GM valley pan sensor besides torquing it to the point it snaps is to drop it. They're more fragile internally than spark plugs.

4' of dropping the knock sensor box onto concrete is enough to make the reliability of the sensor questionable.

I'd imagine you've had that spark plug that fell out of the socket and bounced off a few things on the way down. Looks good externally and then doesn't work when put in again.

Now, what I just said above ^^^^ does not apply to all makes and models. Subaru knock sensors, for instance, will be seriously damaged if over torqued because the bolt passes through the core of the sensor and crushes it.

 

Thanks for the responses..... Autozone brand.... I just replaced the rear.....tq'd them down 15lbs with a snap on tq wrench. I've disconnected the battery and let the system reset.... I also swaped the harness on the sensors.. The front is plugged to the rear harness and front to to the rear. Im gonna drive it a while and see what happens

 

That's were I got mine from. I Hope it last for you this time.