Replace knock sensor and check engine light is still on?

Q32MODULATE

MEMBER
2001 CHEVROLET SILVERADO
V8
4WD
AUTOMATIC
99,500 MILES

I'll try to make a long story short. I bought a 2001 Silverado Z71 2 weeks ago. 5.3L V8. Immediately after I got it, the check engine light came on. Truck is covered by a 50/50 warranty.

The code was for a P0332 knock sensor. Dealer had his mechanic install 2 new knock sensors. Parts were from O'Riley. No new wiring harness installed.

I moved from Ky where I bought the truck to Wy. On the way, the service engine light came on and it is code P0327, another knock sensor.

GM dealership here says they will have to replace the knock sensors again AND put in a new wiring harness. They say the problem was not replacing with genuine GM parts and not replacing the wiring harness.

Ky dealership is balking at paying to have another set of knock sensors put in. Original mechanic says there is no need for a new wiring harness and the knock sensors must be bad. They say GM parts are no different than any other parts and that the GM place is trying to rip me off.

And now, Ky dealership is suggesting I try new spark plugs first before putting in new knock sensors. That's another $200 out of my pocket and I don't think it has anything to do with knock sensors.

Anybody on here know what the real deal is? I just want my truck fixed and I'm not sure who to believe about what. Thanks.

5 Replies

RACEFAN966

MECHANIC
5,029 POSTS

Ok what this code is saying is that the knock sensors and the PCM are not talking to each other. So what that means for you is this. The blue wire and the gray wire between the knock sensor and the PCM need to be checked for any breaks in the wires and if all is fine there then the PCM needs to be checked to see if it understanding the signal sent from the knock sensors. So this codes means that there is either bad wiring or a bad PCM. What they can do is using a scanner and a hammer is see if the computer see's a knock. Set it up to read the votage coming from the knock sensor and tap on the block see if there is fluctuatiing frequency if so then they need to check the dark blue wire from the knock sensor to the PCM for a short to ground. Let me know how it goes.

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Wednesday, August 26th, 2009 AT 10:53 AM

Q32MODULATE

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3 POSTS

First, to clarify, changing spark plugs will not affect this problem one way or the other, correct?

Secondly, the blue and gray wires. Are these accessible without removing the intake manifold? I'm not actually working on the truck myself, but I will be taking it in to the mechanic to have them perform the test you recommend.

I also found this on another forum. The current error code I have is a P0327. From what this says, you seem to be talking about a P0325. Cutting and pasting from the other site here:

I know the GenII engines (1999-2002) had a problem with water getting into the knock sensor mounting holes, and creating codes due to short circuits (Code P0332) for the REAR sensor ONLY. If you have a code P0327
that is for the front sensor ONLY. No need to replace them both. If you happen to have a code P0325, this code means that someone, somewhwers replaced the PCM (computer) and did not swap the Knoch Sensor Module into the new PCM computer.
Testing. Remove the intake manifold sight shield.
Disconnect the knock sensor jumper harness connector located on the left side of the intake manifold.
Set the DMM to the 400K ohm scale.
Measure the resistance of the appropriate knock sensor using the DMM connected to battery ground.
Is the resistance of the knock sensor between 93 and 107k ohms.
If so the sensors are good
If not Connect the DMM between the appropriate knock sensor signal circuit on the sensor side and the engine block.
Set the DMM to the AC voltage scale.
Important: Do not tap on plastic engine components.
Tap on the engine block near the appropriate knock sensor while observing the signal indicated on the DMM.
Is any signal indicated on the DMM while tapping on the engine block near the knock sensor?
If so check all wires to PCM.
If not replace sensor(s) for the code set.

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Wednesday, August 26th, 2009 AT 11:14 AM

RACEFAN966

MECHANIC
5,029 POSTS

I am refuring to code P0327 as you questioned. I am using mitchell 1 on demand for my info that I passed on to you. No the spark plugs will not have and affect on this code not that I can find nor have I heard of either. Now as for the dk blue wire it should be checked as stated.

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Thursday, August 27th, 2009 AT 10:24 AM

Q32MODULATE

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3 POSTS

And now. The rest of the story.

I had the sensors checked, they tested fine. The wiring harness was shot so I had them replace that. The idiots in Owensboro, Ky who did the original work on the truck had REUSED the intake manifold gasket so I had a nice big intake leak. Thanks Horn Automotive.

All was well for a week. Then the SES light came back on. Took it back to the shop, they tested it again and decided it was the PCM module. So I had that replaced (for $500) yesterday.

Driving home this evening, yeah. The SES light came back on. I've now spent over $1000 to fix what should have been an easy problem. And it is still not fixed. It's been to 3 different mechanics in 2 states and no one has a clue as to how to work on this truck. Finding a good mechanic is like finding a good doctor. They're about 1 in a million.

So I give up. I'll drive the truck with a piece of electrical tape over the SES light. It's fully insured so maybe I'll start leaving the keys in it at night. Or I'll just drive the GD POS off into a lake or something.

I've been a diehard Chevy guy my whole life. But this truck is cursed. And I curse the guy that put the sensors UNDER the intake manifold. What a piece of junk.

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Thursday, September 24th, 2009 AT 8:25 PM

ENGINEER1

MEMBER
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It's been a long time since anything was posted here, but I just went through the knock sensor fiasco and learned a lesson the hard way on my 2001 Suburban (225,000 miles). I purchased cheap sensors online for less than $20 for the pair. Installed them and had a SES light a couple days later. After much debate, I purchased a pair of OEM sensors for over $100. Before I put them in, I checked the $10 sensors with an oscilloscope (trace on the left below). The voltage setting was on 200 mV/division, so the signal shown is about 1 V peak-to-peak. I then removed the sensor and replaced them with the OEM parts torqued to the same value. I then did the same test with the oscilloscope (trace on the right). This time, however, the voltage setting is 2 V/division, so the signal is about 14 V peak-to-peak, more than 10 times higher than the cheap sensors. Both cheap sensors has about the same sensitivity (as did both OEM sensors), so this is very unlikely to be just two defective cheap sensors. They just do not have the performance of the OEM sensors. I am all for saving money when reasonable, but if you have to replace knock sensors, do yourself a favor and spring for OEM sensors.

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