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  #16  
Old January 2nd, 2019, 13:37
Ecamacho Ecamacho is offline
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Re: P0715 Diagnosis Input

Hmmm good points. That could very likely be the culprit. I have never seen an electrical problem so abstract like this. I am going to try and get my hands on a good scanner and see if I can monitor the solenoid during the lock up phase as well as the input signal.

Worst case I can hit the JY and maybe grab a new harness and see if that helps anything.

Thanks for all the help I will keep trying stuff and report back on the findings.
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  #17  
Old January 2nd, 2019, 14:13
Ecamacho Ecamacho is offline
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Re: P0715 Diagnosis Input

Quote:
INPUT SPEED SENSOR (ISS)

The TCM uses the Input Speed Sensor (ISS) to detect transmission solenoid functional faults (P0751 solenoid A functional fault, P0756 solenoid B functional fault, TCC solenoid C functional fault). The ISS is a variable reluctance sensor. Changes in the reluctance of a magnetic circuit caused by the passing of the rotor lobes on the overdrive clutch drum result in the ISS outputting an AC periodic voltage wave form. The frequency and voltage of the wave form are proportional to the transmission input speed.

NOTE: SINCE THE OD/CLUTCH DRUM IS STATIONARY IN 4TH GEAR OR WHEN THE VEHICLE IS IN GEAR, BUT NOT MOVING. THERE WILL BE NO ISS SENSOR SIGNAL

Sorry for the double post back to back but I was able to find this over the weekend doing a different type of search related to shift solenoid DTCs. From this, 4th gear will not have an ISS signal when moving in 4th or if it is in gear at a complete stop.
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  #18  
Old January 2nd, 2019, 17:50
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kastein kastein is offline
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Re: P0715 Diagnosis Input

ECU, solenoids, and CPS are unrelated to this, though I can see why you would check them given you're kinda up a creek without a paddle here. TCU, ISS, harness, and the reluctor ring are prime suspects. But you've already checked most of that.

A little electrical theory for the unaware (probably not the op... You seem pretty well equipped and educated for electrical diag, well done so far) - these sensors are what's known as a variable reluctance type gear tooth sensor. Essentially it is a magnetic pickup coil on a horseshoe iron core, but with a twist - there's a magnet stuck to one end. Recall that magnetic pickup coil sensors convert the change in magnetic flux to a varying voltage. So the faster the magnetic flux through the winding changes the higher the instantaneous voltage at that moment in time. Many years ago these were used with a magnet glued to the spinning wheel, until someone clever realized that rather than gluing magnets to a wheel in a pattern, one could glue the magnet to one end of the horseshoe and use a slotted mild steel wheel to vary the magnetic permeability of the gap between the horseshoe tips, varying the magnetic flux and therefore the voltage while simplifying and cheapening production and also making the whole thing more reliable to boot.

Anyways... The peak to peak voltage produced by the sensor therefore depends on a few things:
* Distance from the reluctor wheel surface/airgap (closer means stronger signal, but also can cause sensor damage if there is a lot of run-out in the wheel)
* Reluctor wheel rotation speed (faster means stronger signal)

My guess? Since you already tried replacing the sensor (good), the TCU (also good), and ohmed out the wiring, I bet the sensor has a little too much airgap to function right, since your code is showing up at low speeds. (Though I'd expect to see it at low *engine* speeds, not necessarily travel speeds.). I don't know why it would have that, but try removing it and very carefully cleaning the hole in the trans case that it goes into, the mounting surface, and lubricate the sensor seal/oring before trying to seat it. I might even say shave a few thou off whatever sets its mounting depth but that's irreversible so try that last.

While you have it out, peer into the hole and see if the reluctor wheel is in good shape. It shouldn't be chewed up and should have 16 teeth if you rotate it, though that may be difficult given that you aren't gonna get much rotation through the converter cranking it by hand.
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  #19  
Old January 3rd, 2019, 09:42
lawsoncl lawsoncl is offline
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Re: P0715 Diagnosis Input

Quote:
Originally Posted by Ecamacho View Post
Sorry for the double post back to back but I was able to find this over the weekend doing a different type of search related to shift solenoid DTCs. From this, 4th gear will not have an ISS signal when moving in 4th or if it is in gear at a complete stop.



Doh! So the sensor called "input speed sensor" doesn't actually measure the input shaft speed, and we've been chasing a red herring....
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  #20  
Old January 3rd, 2019, 13:28
Ecamacho Ecamacho is offline
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Re: P0715 Diagnosis Input

Thanks Kastein! I would consider myself a little more adept in the mechanical side of things but this long venture of chasing gremlins have definately opened my mind to the realm of electronics.

Quote:
Essentially it is a magnetic pickup coil on a horseshoe iron core, but with a twist - there's a magnet stuck to one end. Recall that magnetic pickup coil sensors convert the change in magnetic flux to a varying voltage. So the faster the magnetic flux through the winding changes the higher the instantaneous voltage at that moment in time. Many years ago these were used with a magnet glued to the spinning wheel, until someone clever realized that rather than gluing magnets to a wheel in a pattern, one could glue the magnet to one end of the horseshoe and use a slotted mild steel wheel to vary the magnetic permeability of the gap between the horseshoe tips, varying the magnetic flux and therefore the voltage while simplifying and cheapening production and also making the whole thing more reliable to boot.
This is quite and interesting piece of info/history I appreciate that a lot. Back in the school days I vaguely remembered traversing a magnetic field with some type of metal induced some sort of EMF. Faraday would be quite disappointed in my simplistic understanding that is likely incorrect haha. Or at least I think it's Faraday.

Quote:
since your code is showing up at low speeds. (Though I'd expect to see it at low *engine* speeds, not necessarily travel speeds.)
I will correct my thought and concur that it is low engine speeds. I watch the RPM needs and as it sits around the 1k mark as I slow down, boom, the light switches on. I have had some RPM issues that feel like a misfire which is why I included some of the other items in my previous posts. It maybe fluctuates about +/- 30 RPMS, very mild but noticeable.


Quote:
Distance from the reluctor wheel surface/airgap (closer means stronger signal, but also can cause sensor damage if there is a lot of run-out in the wheel)
I will take a look at this. I stuck a small dowel in there and measured the sensor to find that it is a pretty large distance from the top of the reluctor peak to the sensor tip. I put a bore scope in there and quick cranked with the coil and injectors disconnected and I couldn't really see any issue in there but it could likely be an issue. I got some extra sensors so I will hack one up just to test for sure.

Thanks for all the tips and the info. I think it is good to mention I found the post on "Everything you need to know about the AW4" and it looks like you have diagnosed some similar things in there. My fault for bypassing that link; I believed it was too good to be true and I though oh my issue would never be in there...
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  #21  
Old January 3rd, 2019, 13:34
Ecamacho Ecamacho is offline
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Re: P0715 Diagnosis Input

Lawsoncl,

Quote:
Doh! So the sensor called "input speed sensor" doesn't actually measure the input shaft speed, and we've been chasing a red herring....
Ha! spot on! Sadly now I can really feel this Jeep is just laughing at my vain attempts to fix it
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  #22  
Old January 10th, 2019, 10:42
Ecamacho Ecamacho is offline
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Re: P0715 Diagnosis Input

Update: I was able to grind down the input transmission sensor flange a bit, sanded down the mounting surface on the side of the tranny, and I also closed the connectors a bit on the TCU plug since they were a little widened. Right away I noticed an increase in the induced voltage as the sensor picked up the reluctor notches on the OD clutch drum. I tried to get in there and look as well and the notches do not look damaged to me nor would I think they could get damaged because it looks like a 1 piece casting.

Took the rig out for a test drive and hooked up the volt meter to measure AC voltage as I drove. Everything was good and the numbers displayed corresponded with all the shifts and accelerations. However, I think I was able to capture the exact time the Check Engine comes on and I would just like to share. I am positive this is only happening in D shift position.

With the shifter in D, traveling over 35+ when the TCC locks up I noticed when I slow down applying brakes and then letting off the brake to coast to about 20-25 mph when the truck shifts into 2nd the signal drops and stays at about 0.05 VAC until I come to a complete stop and start going again. This was when the light triggered. My brake switch appears to be working properly but maybe the TC is not unlocking or re-locking since it mimics the voltage in the OD condition.

Next steps I guess would be check the brake switch signal input at TCU at set condition, Pressure test the pump at idle for spec pressure, Monitor NSS D 12v signal during set condition.

For reference this is the procedure I used to diagnose:

http://www.zinref.ru/avtomobili/Jeep...NGLISH/889.htm

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