Recently I have been getting knock sensor codes

RICHARD48

MEMBER
2000 CHEVROLET SILVERADO
5.3L
V8
AUTOMATIC
150,000 MILES

Recently I have been getting knock sensor codes from both sensors for several weeks. I have a code reader and have been clearing the codes and noting my driving when they come back. I noticed that the check engine light comes on when there is no load on the engine as in going down hill. There is one down hill grade that I can make it come on by taking my foot off the gas quickly.
I have been looking at the forums for weeks and have found nothing indicating why this would happen under deceleration or no load situation.
Thanks
Richard48

5 Replies

HMAC300

MECHANIC
48,601 POSTS

It could possibly be a bad knock sensor doing this. There is a bulletin on this as well, but I need the code to see if it applies. Here is an article from this site with information on scanning for codes.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

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Wednesday, May 5th, 2021 AT 2:16 PM

RICHARD48

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6 POSTS

I will post them as soon as it gives me a check engine light. I deleted them yesterday and have had it out today and this is the first time in two weeks I have drove it without getting a code.

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Wednesday, May 5th, 2021 AT 2:16 PM

RICHARD48

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6 POSTS

Finally, got a check engine light today. It happened pretty much the same way it always
has. Driving 55-60 going down hill and as soon as I took my foot off the gas I got the
service engine light. As I mentioned earlier it always happens at about the same speed
in deceleration. I have not had the light come on at lower in town speeds or under heavy load during acceleration.
The code reader showed a P0327 and a P0332 which from what I can find is both sensors.
I have a few question so I can better understand what is going on.
1. From what I read, upon starting the engine the sensor sends a signal to the computer
which is an indicating the engine is running. If the sensor is bad and sends no signal, will you get a check engine light immediately as an indication the sensor
is not working?
2. If the cable is bad killing the signal from the sensors do you get a check engine light
immediately?
3. When the computer gets a detonation indication from the sensor it retards the spark which should hurt performance. Does the computer reset the spark to the normal
setting if it sees no further detonation signal from the sensor or does it stay retarded until the code is removed? I have never noticed any loss of performance when these codes are generated.

Thanks
Richard48

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Wednesday, May 5th, 2021 AT 2:16 PM

HMAC300

MECHANIC
48,601 POSTS

A knock sensor only works by Hertz so if doesn't hear knock nothing happens. When these go bad it is normally a good idea to replace the knock sensor harness under manifold as they go bad as well. When the timing is retarded the computer if not sensing any knocks from knock sensor automatically goes back. If the computer sees no signal from ANY sensor it sets the light.

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Wednesday, May 5th, 2021 AT 2:16 PM

RICHARD48