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Old 08-23-2019, 04:55 PM
ole.gray ole.gray is offline
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Default Testing knock sensors

Is there any way to test the knock sensors on a 04 Silverado with a Solis edge. This scanner is new to me just learning about it.
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Old 08-23-2019, 05:52 PM
kirkbarrow.garage kirkbarrow.garage is offline
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Originally Posted by ole.gray View Post
Is there any way to test the knock sensors on a 04 Silverado with a Solis edge. This scanner is new to me just learning about it.

The best way is to look in the data setting of the engine ecu unit, scroll down to find if it can display knock sensor results, look at the reading and then tap the block with an 8oz hammer and watch to see if result changes ( or not ! )
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Old 08-23-2019, 06:52 PM
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If you're getting a code, check the resistance on them. They should be around 100k ohms. If one is bad, it is recommended to replace them both, along with the harness. Torque them properly.

Joe
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Old 08-24-2019, 03:59 PM
ole.gray ole.gray is offline
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Ty for the info. Will try checking it when I am off.
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Old 08-25-2019, 05:12 PM
David Green David Green is offline
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Quote:
Originally Posted by kirkbarrow.garage View Post
The best way is to look in the data setting of the engine ecu unit, scroll down to find if it can display knock sensor results, look at the reading and then tap the block with an 8oz hammer and watch to see if result changes ( or not ! )
May I ask, is that a reliable way to test the sensors/circuits?

I know it can be checked that way but I was of the understanding that the PCM is designed such that the circuitry is such that it is looking for combustion knock at a frequency range programmed in!

Or am I out my depth in my thinking!
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Old 08-26-2019, 07:09 AM
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normally what i do, is go to the harness side of the engine ecu. with the harness disconnected, i use a scope and pin out the knock sensor at the connector and then hit the block next to the sensor and watch for voltage on the scope. compare to specs and make sure its working ok.
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Last edited by tech25; 08-26-2019 at 11:18 AM..
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Old 08-26-2019, 02:58 PM
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That question is a can of worms. The best thing to do is to read how that particular system works. Creating a knocking noise on the engine and looking for retard on the scanner can still work, but not like it did years ago. Watching the knock signal on a scope is pretty reliable, but won't necessarily let you know if the bias voltage is incorrect.
On the engine that ole.gray is working on the service info states that the PCM only looks for knock when a cylinder fires. You'd have to create a knock right when a cylinder was firing for best results. The PCM does some other stuff that is hard to see on a scanner too. It learns the minimum noise level of that engine and then filters that noise from the circuit. As a Tech, you have know way of seeing that info. Most scanners, including OEM rarely, if ever, give you all the spark info.
For example, the truck in question uses the following info to determine total advance:
Coolant Advance
IAT Advance
Cranking Advance
Idle Advance
AFR Advance
Smoothing Advance
Knock Retard
Burst Knock Retard
Knock Learn Facor
Startup Retard
If you can't see all the PIDs it's tough to know how to test it in a generic fashion.

So if you ask me, check the knock sensors like the service info recommends and you're pretty likely to diagnose them correctly.

My 2 cents (actual street value even less)
Joe
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Old 08-27-2019, 12:33 AM
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Well Joe.
I'll agree with you on one point and disagree on another.

Firstly, I'll agree with this statement... (which is so very true)
""That question is a can of worms. The best thing to do is to read how that particular system works""

Secondly, I'll disagree with your last statement... (it's worth much more-!!)
""My 2 cents (actual street value even less)""

The systems used (and not just knock sensors) vary widely. Each manufacturer does things a little differently, so, reading up on the THEORY AND PRINCIPLES OF OPERATION is a must, unless one wants to go down the hand holding guided fault finding methods which usually employ the "substitute X-part, if no good, substitute y-part" procedures.
Some systems look for voltage changes, some look for frequency changes, some look for amperage changes.
Then , if only the manufacturers would specify the amplitudes of the various signals, comparing the tested values to the design parameters, we can accurately isolate where a fault is, and verify where it isn't.
The manufacturers engineers HAVE TO have these parameters, otherwise they couldn't even build the systems.
If only this information was actually put in the service and repair manuals, which quite often, it's not.
Sometimes it's in there, sometimes it's not, but reading up on the system is the first place to start, on any diagnosis.
Your 2-cents is worth much more than stated-!!
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Old 08-30-2019, 09:11 AM
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Thanks Crusty,
You have always beat the drum for getting all the relative info, and getting it correctly. I agree with you there! One of the things I missed the most from leaving the dealerships to working in the aftermarket was the difference in the service info available. The OEMs don't get it right 100% of the time, and even in this particular case only part of the info is available. I just worked on 2 vehicles with U codes and finding the locations of components and connectors was a total chore. I'd have repaired them in half the time if the info was present, or in the case of the first truck, if it was correct. It's even more important when the trouble tree doesn't work.
Back on topic, I've seen more than one Silverado that had knock sensor codes that simply defied being diagnosed on performance tuned vehicles. The last one I worked on was easy though. It got some water under the rubber cover. See pic. A couple of others tested just fine but would set a code on a short road test. Having a complete understanding of how that code set would sure be helpful, but as we've already hashed out, info on knock sensor codes is sparse.
Joe
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Old 09-01-2019, 02:00 PM
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Joe, The next time you have a new one, hook up a meter and tap on it. Then take one that's crusty like that and tap on it. Watch the rate of resistance change. You will likely see a crusty one doesn't change nearly as much.

That style you have to use OEM sensor and an OEM harness if the harness is damaged.

I have Used the dorman sensors and had an issue. I have used the Auto parts store brand sensors and while it looks exactally the same as OEM and has a generic parts store box, they don't last and often come back with the same issue.

Even My own truck, used a local parts store sensor and RTV damn. Lasted 90 days and failed again. Tried to save 10 Bucks and was in stock Vs. waiting a day to get it.

Come to find out the local parts store warranty was only 30 days on electrical items... So being out the money I wasn't going to chance another parts store part. OEM part with with revised RTV damn. Problem solved!

Same with everyone else that's tried to go cheap And fix it themselves, Then asked me to repair it when it fails.
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