It sure is, the data input can become intermittent do to a failing PCM. I would search google or ebay for a pre-programmed rebuilt unit and install it, here is how in the images below. Check out the images (below). Please let us know what happens.
ME: And after updating my scanner and figuring out where the trans LD was I checked it out today and this is what I discovered, I posted this reply today to 2CarPros:
EDIT: Then I asked them this question:
OK, I have not replaced the PCM Yet (new TCM still), trans still feels normal, but on live data (I am using a much cheaper scanner this time) at idle in park the TCC slip speed is 678ish RPMS (vey close to engine RPMS), and it goes up and down as it should when giving it gas and letting off, but the ISS is 0 RPMS no matter the engine RPM in park, power torque the engine in drive up to about 1700ish RPMS and the TCC reads normal, but the ISS is still showing 0 RPMS…
Now put it in drive or reverse, and once the VSS shows 2 MPH (car moving) the output speed sensor starts showing the RPMS (normal) and the ISS starts showing RPMS above about 350-380 RPMS, then everything looks normal, the TCC applies and the TCC slip speed RPMS drop to about 14 RPM (normal) (and I ran out of road, testing), but when I let off the gas and apply the brakes the TCC slip speed goes crazy, up to 8100+ RPMS and back down again to normal, then while coming to a stop (every time), the ISS right about 350-380 RPMS and at about 2 MPH the ISS drops off back to 0 RPMS, TCC slip speed still normal 670ish RPMS…
And since the TCC slip speed looks normal (mostly) but the ISS doesn’t show any RPMS until the car is moving above 2 MPH, does this confirm the PCM requires replacing??
So what do you Pros think about it being the PCM now??
I’m so frustrated with this car, if I hadn’t of just put brand new Firestones on it, I would just about sell it for junk at this point… but with new tires and all the other parts that have been replaced on it in order to test drive it (including $85 for new tags), I am in it to deep to stop now…
Also waiting on the use of a Pro scanner has taken up most of the down time dealing with this code…
BTW Flagship One out of New York was great dealing with, and it looks like I will be using them for PCM if confirmed it is bad or once I give in and just order one and cross my fingers…
Here is 2CarPros reply: With these numbers I would try replacing the input shaft speed sensor because it sounds like it is defective.
ME:
If the TCC Slip Speed RPMS are correct and the trans is shifting correctly, how can the ISS reading not be correct, I am pretty sure the TCM gets the TCC Slip info from the ISS before calculating the Slip Speed RPMS… Unless I am way off on this…
I am more and more thinking this is a PCM issue like advised earlier by KEN L from 2CarPros, or possible software issue with the scanner, but it reads normal on the Infinity… gawwwwd I hate computers sometimes… They have their pros and cons, but this is a con right now…
That is really strange. Your low speed results mimic a bad ABS speed sensor I had once. Below a certain speed, it was dead. As the speed increased, so did its output voltage level and then the ABS module could see it (above the input voltage threshold). I could make it work by reducing the spacing between the pickup and tone ring but in the end, it was a bad sensor that lost some of its gain.
The wild reaction on deceleration is harder to rationalize unless something is moving in the trans regarding the pickup or sensor.
Absolutely. The sensor can have a defective or marginal output. But the device reading the sensor can also have a damaged input causing strange behavior. Only way to tell for sure is to gain access to the raw signal and measure it against a spec. Then make sure the device reading the sensor output isn’t loading it down for some reason…
Agreed, but the TCC Slip Speed RPMS work as it should, there is no dedicated sensor for the TCC Slip Speed RPMS, the (2 wire) ISS sends the generated voltage signal to the TCM and then the TCM calculates the TCC Slip Speed RPMS based on the ISS & VSS (output shaft speed sensor) signals… The TCC Slip Speed RPMS are correct, so how can the ISS signal be bad, but the TCC Slip Speed RPMS are correct??
Yeah, that one is on me, I wasn’t thinking about this being normal as the engine drops to idle and the transmission internals are still moving at the speed of the car until stopped. Oops… lol
With the transmission harness unhooked at the trans, I then hooked up the DVOM leads to the two ISS wires at the case harness and read the generated reference voltage from idle to 2000+ RPMS and the volts were as smooth as silk…
OK, I thought the Slip Speed was calculated based on engine RPM minus ISS RPM.
Going back to P0717- saying the ISS signal is missing and yet your TCC Slip Speed value seems to be correct…You indicated earlier there is a reference signal output from the TCM to the PCM to indicate ISS function? Do you have a snippet of the schematic you can share?
If the ISS goes into the TCM, gets used there to derive TCC Slip Speed, then gets transformed into a reference signal to feed the PCM, it would seem the only logical conclusion is either a bad connection or the PCM input is bad…I hate to make any conclusions like this without a better understanding of the relationships involved…interesting problem nonetheless… oh, and easy too (once you know the cause)
Since you plug the scanner into the ALDL, that is directly linked to the PCM, doesn’t the PCM have to get the info from the TCM through the BUS link (???) in order to show the TCM Live Data??
I’m thinking (as well as Ken L from 2CarPro said it could happen) that the info is being corrupted somewhere between the TCM bus to the ALDL connector, meaning the PCM… Most every under wiring harness is cut open and all the wires look good…
Also, with the OE TCM, the trans was shifting hard and hunting gears, etc with only the P0717 code (well P0700, but that is a given) for the transmission, once the new TCM was installed, the vehicle now drives perfectly normal, took it on a long test drive this morning, 1st, back roads with lot of steep hills and fun curves to the next city over, then took the 65 MPH HWY back to the house with a few hills and curves between the to…
SO if the TCM was not reading the ISS correctly, the transmission would not be shifting correctly… just can’t get ride of that flipping P0717 code… Yes we did a hard reset after about 20 code deletes, any a few more code deletes afterwards…
Yeah I guess it does in a way anyway, the Slip Speed is the same as the ISS mostly at idle and once above the stall speed and then lock up is applied and it changes to 0-20ish Slip Speed RPMS, it calculates Slip Speed based on engine RPM, ISS, OSS/VSS, gear ratio, TCC lock up engaged or not, and engine load/engine torque produced…
Crap, now my head hurts and I am confusing myself…
Well, I bit the bullet and took a gamble and lost, I ordered a new PCM, while we (my son and I) were waiting on the PCM, he noticed a large puddle of ATF under the car, no big deal, the axle seal gave up the ghost, replaced and not leaking anymore… Installed the new PCM, then programed the key and it started right up, spit out lots of codes, did a few start ups and then cleared the codes, ran great, but the new P0315 crank sensor variation not learned will not go away (yet), again starts normal and drives normal… but the dreaded P0717 is still there… I hope the P0315 will go away on it’s on, or does anybody here know how to do a relearn on it… (haven’t tried friends pro scanner)??
So now I need to get a schematic between the TCM and the PCM… If that checks out, next is pulling the trans and replacing the internal harness and the ISS (possibly dealing with what @db4690 posted in reply 9)…
The 4T45E’s have a Pressure Regulator Valve and Bore Wear known issue that is one of the main causes for transmission failure, as well as the pump slide spring tends to break… The repair kit with a new upgraded pump slide spring should be done anytime the VB is removed from the trans if not already done…
So the PCM would have been the cheaper of the two (PCM vs internal harness, sensor, ATF, VB repair kit and tools), basically I most likely had a 50/50 shot at a new PCM fixing it…
The Cobalt might just be driving around with a P0717 code until it starts acting up again…
