CKP Active Counter Graph; Intermittant Loss of CKP Signal

[Goldwing2000]

2011 Tahoe LS 2WD, completely stock, 150k miles, Texas vehicle so no excessive corrosion issues.

 

Looking for a screenshot of a known good CKP Active Counter chart line or a definitive opinion on the one below. Chasing down the infamous intermittant CKP signal loss and as far as I know, the active counter should steadily increase until it gets to a high value and then drop back to zero.  My CMP Active Counter does this but my CKP Active Counter (when it works) is all over the place and fluctuates wildly.  For reference, CKP AC on top, CMP AC on bottom:

 

 

I feel like this is an issue but the only other vehicle I have to compare to is a 2018 Mazda and it doesn't use a CKP Active Counter at all.  If this is normal, then I can start looking in other areas.  If it's not normal, I can start to figure out why (suggestions welcome).  

 

The root issue I'm trying to solve is an intermittant loss of signal from CKP (Circuit A).  Textbook signal loss symptoms: Engine will crank for an extended period and then start off of the CMP signal in low-power mode with no tachometer and stabilitrak warnings.  Happens maybe 50% of the time.  If I shut it off immediately and attempt to restart, it will usually set a P0335 code.  Most times If I drive long enough to warm it up, then shut it off and let it sit for 15-30 mins (shopping visit, getting gas, etc), it will restart normally and run fine.  Almost like something (maybe the CKP sensor) is heat-soaking and making contact, then allowing a normal restart on the next cycle.   Turning ignition off and then immediately restarting does not clear the issue.  It has to sit for a little while.

I'm already well aware of the standard P0335 diagnostic procedure and will do that eventually but I haven't been able to catch it when it's actively failing.  Most times when it happens, I have somewhere to be and don't have time to look at it.  By the time I get home it's already working again.  I've read quite a few accounts of other people who have had this problem, gone through the procedure, replaced CKP or ECM or both and still not solved the problem.  I'm trying to be more methodical and not call in an artillery strike from the parts cannon.  The battery is new (needed one anyway), the alternator charges correctly and the main ground on the left lower engine block is intact and not corroded (life in Texas, yo).  Voltage at battery exactly matches ECM/OBD voltage, so bad battery cables are doubtful.  I already replaced the CKP connector and the ignition switch (thinking it might be an intermittant power signal to the ECM... they're cheap parts).  Have not replaced the CKP sensor yet but it's in my cart to buy (Genuine GM, of course).  

 

Any input is appreciated.

 

Thanks

Edited April 21 by Goldwing2000
grammar

[davester]

maybe try wiggling the harness along it's length, w the engine running and while watching it log if you can?  For my '12, I believe the harness goes across to the engine, then down under the front of the engine, then back to the ckp sensor.

[Goldwing2000]

17 minutes ago, davester said:

maybe try wiggling the harness along it's length, w the engine running and while watching it log if you can?  For my '12, I believe the harness goes across to the engine, then down under the front of the engine, then back to the ckp sensor.

Thanks.  That's going to be my second step after I do all the normal P0335 tests next time it glitches.  But the first thing I need is for someone to verify if that graph line is normal or fubar.  My gut feeling is fubar but GM vehicles are not my specialty and it runs perfectly fine when I'm getting that line.  I would think that if the CKP signal were making and breaking that often, it would show up somewhere else (misfires, unsteady rpm signal, etc).  Everything else is rock solid on the times when it starts normally.  

[Jsdirt]

Unless something changed on the newer ones, I've always expected CKP sensor output to be a square wave. Either on, or off. Shouldn't be any "hash" like in the 1st pic.

 

Could just be your scan tool, but since you have a CIRCUIT code I'm suspecting wiring or a connector. You'll have to rule that out from the sensor all the way to the engine computer. Could also just be a cooked sensor, so keep that in mind.

[Jsdirt]

Also, how the graph is set up will make a HUGE difference in how things appear on a graph / scope.

 

Here's an example of the same crank signal at the bottom of each pic. One is zoomed OUT so it looks like pointy spikes, but in reality it is just like the 2nd pic - a square wave. The square one is zoomed IN.

 

Dammit ... can't upload pics to this site for some reason - only site on the net that has this issue! 

 

 

To give credit where credit is due, the 2 pics are from ScannerDanner's (Paul Danner) book "Engine Performance Diagnostics" available here - this is your best bang-for-your-buck in the automotive industry: https://www.aeswave.com/cart.php?m=search_results&headerSearch=Y&search=paul+danner

 

He also has web page with hundreds of educational videos for just $14 a month - nowhere will you find automotive education that cheap! : https://scannerdanner.com/

 

https://postimg.cc/Y43T1yRG

 

https://postimg.cc/yJP2FrjK

Edited April 21 by Jsdirt

[Goldwing2000]

47 minutes ago, Jsdirt said:

Unless something changed on the newer ones, I've always expected CKP sensor output to be a square wave. Either on, or off. Shouldn't be any "hash" like in the 1st pic.

 

Could just be your scan tool, but since you have a CIRCUIT code I'm suspecting wiring or a connector. You'll have to rule that out from the sensor all the way to the engine computer. Could also just be a cooked sensor, so keep that in mind.

 

We're not talking about the CKP *sensor* output.  We're talking about the CKP Active Counter output (as pictured).

[Jsdirt]

EDIT: It's a pulse tally. I was looking at it from a mirror perspective from the sensor. I've never used that function for diagnostics.

 

Either way, if you've got a circuit code chances are there's a wiring, connector, or computer problem. A better way to get a grasp on what's happening is to scope the sensor output.

Edited April 21 by Jsdirt

[Goldwing2000]

1 hour ago, Jsdirt said:

EDIT: It's a pulse tally. I was looking at it from a mirror perspective from the sensor. I've never used that function for diagnostics.

 

Either way, if you've got a circuit code chances are there's a wiring, connector, or computer problem. A better way to get a grasp on what's happening is to scope the sensor output.

 

Thanks.  Yep, I'm aware that it's a pulse tally.  That's why it doesn't make sense that it's not showing a linear progression.  It's fluctuating rapidly up and down, which is why I'm trying to get someone who will check the same parameter on their own vehicle (or knows for a fact what the line should look like).

 

And yes, well aware of all of the parts of the circuit and how they interact.  Unfortunately the problem is intermittent (currently no codes) so I'm trying to find anomalies with available data first.  I'll get to checking waveforms eventually but even when the code is active and the tach isn't working the live data still shows sensor rpm, just no engine rpm.  So the sensor is putting out the signal and the ECM is reading the signal but the information isn't getting where it needs to go from there.

 

Anyway, for now I'm just looking for a yes or no from someone about the active counter graph.  Once I have that, I'll go from there.