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P0715 Diagnosis Input

Ecamacho

NAXJA Forum User
Location
CA
I got a 2000 Cherokee Classic 4x4 at about 300k on the clock and recently had some weird issues with a recurring p0715.

Here is a "small" condensed list of things I have looked into based on my searches and diagnosis:


- Verified trans fluid level at operating temp in neutral on level ground

- Tested TPS per testing guidelines (5v ref, ground, singal, using analog meter to see the voltage changes) everything within spec and tried a spare I had MOPAR OEM

- Cleaned and tested all grounds on chasis/engine bay with <= 0.02 ohms at each point

- Cleaned NSS, verified 12V signal thru TCM plug in each gear. Verified continuity on the pins in the engine bay harness. Starts in P and N and reverse lights work

- Changed out the transmission input and output speed sensor OEM MOPAR and tested for 500-700 ohms, checked out. Also, measured AC voltage to verify pulse generation gear 1-3. No AC voltage signal present in 4th gear on the input side?

- Had a spare TCM from a 1999 and still triggers code

- Tested the wires from the input speed sensor to the TCM and to the PCM. No shorts to ground or short to voltage according to the test procedure in alldata

- Replaced all shift solenoids because the old ones had some high resistance values on the 2nd

- New Dex 3 fluid poor man flush 3 times and new filter. No metals found in the pan

- Checked CCD Bus +/- signals through TCM connector and dash cluster and they check out

- Checked the brake switch at the pedal for proper adjustments and voltage and it checks out no TCC lock/unlock problems

- Replaced my CPS because it was old and was being wonky with OEM sensor MOPAR

- Forgot to mention I have adjusted the kick down cable using the procedures from the manual I found online


I think that was everything. Sorry for the super list. Anyway, I am trying to see if I missed anything or if anyone has experience with this issue. The car doesn't go into limp mode at all and still shifts which is super strange. When I shift to 3rd and leave it there the MIL does not come on and when I drive over 20 mph in D the MIL does not come on. Only at low speeds there seems to be an issue and I get the P0715.:flamemad:
 
I don't even see a P0715 code listed? Are you getting that with a scanner?
 
RCP PHX,

Yes my scanner picks it up as the p0715 Input/Turbine Speed Sensor Circuit A.

I used 3 different ones to confirm but there are some variations:

Autel: P0700 and that's it

Snap On: P0700 in trans module and P0715 on the PCM

Cheapy Bluetooth: P0715

I should prob just start looking for another transmission haha.
 
What I read was a "communication" issue between the ECU and TCU.
 
Cool thanks for the info. I will double check the wires from the tcu to the pcm. Maybe I have a faulty pcm that isn't properly converting the sin wave to the square wave signal.
 
measured AC voltage to verify pulse generation gear 1-3. No AC voltage signal present in 4th gear on the input side?


That seems very odd. Was that with the sensor disconnected from the trans computer? The input shaft speed sensor shouldn't be affected by what gear you're in.
 
lawsoncl,

That is the read out when I put the volt meter in the connector on the input pins. The sensor is still connected at this time and I am driving the car around.

I have voltage as I increase speed when the shifter is in 2 & 3. As soon as it is in D/4, there is a signal up until the trans shifts into 4th then it drops from like 1-3.5 ish volts to 0.003 volts.

As soon as is down shifts, then the voltage signal comes back i.e. 3, 2, 1 gear. I was under the assumption that even though you are in 4th or overdrive and there is a 1:1 ratio input to output the shaft still spins. It's as if the shaft no longer is spinning which sets the CEL as I slow down.

I also have a replacement TC on hand and I need to replace the pump seal and transmission shaft seal. Just trying to figure if I need to tear into it and replace internals.
 
Very odd. I think I'd try to measure it at the sensor with it disconnected. It should shift okay, but you could pull the tcu fuse so it starts in 4th.
 
Good idea I will go ahead and disconnect the TCM and see if I can get a voltage reading directly from the sensor. Maybe I'll hook up an O-scope to it to see the waveform. That would be crazy if 2 TCM's in a row were bad and needed to be replaced. I haven't tried this yet so I will for sure give it a shot.

Thanks for the suggestions!
 
You can also set the parking break and put the xfer case into neutral if you want to "drive" it in the driveway. That's what I did when I was scoping the rear output signal. I vaguely recall the voltages on the rear got up to about 30-volts with it disconnected at speed in 4th gear.
 
tried using the method and I was getting an input signal due to the shaft rotating when I had the xfer case in N. Still no signal in 4th/OD. Can anyone confirm this?

I disconnected the TCM and all the shifts points are good with no slipping or popping out of gear to a higher gear.

Might be looking into sending the PCM to a place to check for errors like a bad transistor or something.
 
True but I think the TCM has to send the output signal to the PCM and the PCM could potentially be misinterpreting the data stream. Well at least that's my logic.

Might just run a 2 wire jumper to bypass the wire to the TCM from underneath...

Maybe my sensor wires are backwards? I believe the red and black is the left wire when you go under and look at the sensor and the white one is on the right. Can't seem to get a good diagram of this.
 
True but I think the TCM has to send the output signal to the PCM and the PCM could potentially be misinterpreting the data stream. Well at least that's my logic.

Might just run a 2 wire jumper to bypass the wire to the TCM from underneath...

Maybe my sensor wires are backwards? I believe the red and black is the left wire when you go under and look at the sensor and the white one is on the right. Can't seem to get a good diagram of this.




The P0715 code comes from the TCM. The PCM doesn't know (or care) what the tranny input speed is. I wonder if you have some sort of short between the input sensor wiring and the t/c lockup solenoid? So that when the t/c solenoid is powered that it's messing up the speed sensor? Sounds far fetch, but then again the symptoms are really strange.
 
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.
 
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.
 
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.
 
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....
 
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.

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.

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.


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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