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Knock Sensor Issues Won't Go Away


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Hello all. It's been quite a while since I was on here last but I'm having some issues that I thought the great minds on this forum might be able to help me with. So my '01 Sierra's SES light started coming on a few months ago so I pulled up the code and sure enough got the P0332 Knock Sensor code. I just replaced the knock sensors and harness less than a year and maybe 10K miles ago so I decided to clear the code and see if it came back. For about 2 months and another 5K or so miles the code didn't come back and the truck ran fine. Then my fuel pump went out so I replaced it and on the test drive the SES light came back on and I started hearing the valve clattering that I've heard in the past when that 332 code used to come up.

 

So I went ahead and ordered new sensors and a new harness again just to be safe, and after getting it all back together I took it out for a drive and everything seemed good at first but after about 10 miles the SES came back on and I could tell the truck went back into "limp mode" with the lack of power and valve clattering. This is the 4th time that I've replaced the rear knock sensor and the 2nd harness I've put on and I'm still getting the codes. Any ideas as to what it could be or how to fix it? I'm getting tired of taking that bleeping intake off.

 

Oh and it only seems to have problems and throw the code in the summer time when it is very hot outside (100+ degrees).

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Also are you sealing the sensor covers to the valley cover per the TSB? If moisture is getting in there ic could upset the sensors. But as Rob said, Time to have it diagnosed using a shop scanner such as the Vertronix Tech 2 that the dealer has.

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Yeah I sealed the covers to the valley pan. I have a scanner but its not one of the shop scanners you talked about. Guess I'll end up having to take it somewhere that has the type of scanner you mentioned because today it showed both the PO327 and 332 codes so something isn't right.

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I agree with govtech4, I doubt it is the knock sensors. All I have done under the hood of my 2001 is change the oil, everything else is stock and original. Knock is fuel, timing and spark. The engine controler monitors the fuel quality (a sensor to check) and sets the timing. Nothing you can change or adjust there anymore. But to get knock your fuel is igniting early. I doubt it is the plugs, if you have knock they are firing. It would seem to me it could be a fuel issue especially when you mention the 100+ temperatures. You could pull an easy plug and check for deposits. Deposits can give you hot spots in the combustion chamber which can cause pre-ignition. It could be so-so fuel as well. You could try a 1/4 tank of premium and see if that makes a difference. The heat will vapourize the top end of your fuel. It could also be getting some vapour in the fuel line if it is running close to a hot area of the engine. The fuel lines do run close to the exhaust right around your feet and the catalytic converter is right there too.

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Ok so I haven't had time to work on the truck, but will tomorrow. After doing some research I have a couple of questions. 1) I didn't torque the knock sensors to spec (15 ft/lbs. if what I've read is right) I just tightened them down with a 1/2 in drive ratchet. I don't think I over-tightened them. If anything I didn't tighten them enough for fear of stripping the threads. Could not torqueing them to spec cause issues? 2) Can using aftermarket sensors cause issues? First time I did the change I used GM sensors and it worked fine for about a year but then started having issues. So I tried aftermarket (BWD from O'Reillys) and once again they worked fine for about a year or so. Same thing with the third time. This time since money is tight I ordered aftermarket ones off of eBay. Are these computers really that sensitive to aftermarket sensors?

Edited by jdaniel83
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tried using bwd sensors for a brake light sensor issue I had and they actually made my problem worse, went with the acdelco from the dealer and fixed the problem, and was actually cheaper than the bwd ones from oreillys. So i'm not a fan of bwd.

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I would use AC Delco sensors, make sure to clean out the sensor chamber and once you put the new ones in RTV the rubber boots down so moisture does not get in and corrode the sensors again.

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Well I finally got some free time and got the intake back off this morning, and it seems that the knock sensors were a little loose. They were only torqued to about 8-10 ft/lbs so I tightened them down to 15 ft/lbs, used di-electric grease on the connectors, and put the RTV on each of the boots and where the wires go into them. I would have replaced the aftermarket sensors with some AC Delco or Delphi but the only place around here that had either wanted $90 per sensor, and I cant afford nor do I see spending that much on them when I can get them off eBay or from RockAuto for less than that for both. Plus I have to leave town and need my truck tomorrow so I'm going to let the RTV set overnight and hope for the best on the road trip tomorrow. If I'm still having problems I'll take it in somewhere that has a better scanner than me and see what's really going on. Thanks for all the suggestions. Wish me luck.

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Just thought I would update. I took off on a road trip and for the first 200 or so miles the truck ran great. No SES light and no valve clatter. Then the SES light came on and the valve clatter began again and continued for the rest of the 800 mile trip. The truck seemed to be running ok besides the valve clatter. Power was better than it had been before the sensor change and MPGs were better also. Still when I got home I pulled the codes and sure enough 0327 and 0332, so I ordered some AC Delco sensors and GM harness to replace the aftermarket ones. As soon as they come in I'll tear it all apart again and replace the sensors/harness again. Hopefully the better sensors will fix the problem, but I'm still going to take the truck into a place with a better scanner so that maybe they can tell me if there's some other issues going on.

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