E38/T42 4l65E (no ISS) TCC fix???

[vette5797]

I have a 62 Corvette/LS3/4l65E E38 OS 12617631 /T42 OS 24239927

After a few short drives my TCC stops working and gives code P0741 "TCC system stuck off". Clearing the DTCs allows normal operation again for a few short drives until the same occurs again. Searching all the forums, I've learned that apparently the E38 needs to see an ISS signal. Another forum suggested that although their system didn't have a cure that EFI Live (which I have) did have a fix for this. I found D7026 Input speed sensor, and changed it from yes to no, hoping that this was the fix, but it didn't help. Can somebody tell me what the fix is? All components are new GM over the counter, so I'm confident that it's a tune or install issue. Any help would be greately appreciated. Thanks, Gary

[joecar]

Does your 4L65E have an ISS sensor...?

[vette5797]

Hi Joecar. Thanks for responding so quickly. No it doesn't have an ISS. It's a GMPP purchased two years ago when the project began. Scanning while driving shows TISS as zero, and TCCslip appears to be engine RPM. Gary

[slow67]

What about also turning off P0716 and P0717?

[vette5797]

The DTC codes p0716 and p0717 are still shown as reported codes, but they are not showing up. Only P0741 shows up.
I've also read a number of posts with related issues saying to set C5601 "misfire detection max temp" to 1degree. Neither my ECM nor TCM show that parameter. C0611 seems to be the closest thing I could find. Is that the same parameter for this system? Should I try setting it to 1 degree??

[Taz]

Hello vette5797,

Can you post your original (never modified) ECM & TCM tunes ? Don’t mind taking a look to see what (if anything) could be done.

From memory, when the ECM runs the trans slip diagnostic, about a 250 RPM difference between the ISS and the VSS is allowed (that number may be different for various applications - just intended as an example).

I don’t recall if a DTC is set if the values from ISS and VSS are the SAME. If not, perhaps slicing the ISS into the VSS would be a “hardware” fix for your VSS only transmission.

Just a thought …..


Regards,
Taz

[slow67]

If not, perhaps slicing the ISS into the VSS would be a “hardware” fix for your VSS only transmission.]

Problem there is, the ISS on a 4L70 (I'd assume 4T70 would be the same) is the ISS wheel is 17 tooth, and VSS wheel is 40 tooth.

[Taz]

Good point ... didn't know that ... good news is that 17 tooth reluctor is the same as the manual transmission (I believe). In the TCM .. H0103 ... in the speed calculator ... can set the VSS reluctor to either 17 or 40.

If there does not end up being a "tuning" fix ... then replacing the 40 tooth reluctor with a 17 tooth ... would allow the ISS and VSS to "share" a signal.

Right now we're just "bench racing" as they say ... once the tunes are posted, a "work around" may present itself.


Regards,
Taz

[Taz]

Hello vette5797,

Sorry … focused on your transmission issue and didn’t answer your misfire question.

If the engine is a GMPP crate engine, with no modifications, I would recommend leaving the misfire diagnostic active - often helps sort out issues (i.e. defective coil, poor connection to an injector, etc.).

Sometimes when an enthusiast installs a larger cam, or makes other modifications, rather than working out the “best” tune, or appropriate diagnostic parameters for the particular application, they simply turn things “off”.

While this approach is quick and easy, it fails to fully utilize the PCM’s (or ECM, TCM) ability to monitor the engine / transmission. There are times when this approach may be necessary, or partially necessary - but is properly used after tuning solutions have been exhausted.


Regards,
Taz

[vette5797]

Thanks Taz, slow for the help. Yesterday I went ahead and changed c0611 to 1degree, reflashed and went for a drive with the v2 scanning. Misfires stayed at 0 but after about ten minutes the TCC quit again. So I think that rules out misfires as the cause. I did find out though that by just shutting off the car and starting back up that the TCC will work again for a short while, even though the p0741 is current. Is there anyplace I can find the list of parameters that set P0741 on a 2008 era 4l65E. I've googled my butt off but can't find much specific to the 4l65e. Also, I don't know how this trans compares to the aforementioned 4l70 or 4t70 transmissions.
Regarding the tunes, this project started over two years ago right when the LS3 became available over the counter from GM. The GMPP complete LS3 package still wasn't available yet so I ended up with the long block version and had to purchase separately the intake,rails,injectors,coils etc. The LS3 intake wasn't available, so the Holden version with diffrent MAP sensor was used. I tell you this so you'll understand why the MAP is scaled and other mods. My original tuner started with the 2008 Silverado ECM and TCM tunes, apparently one of the only ones available at the time that used E38 and T42. Later, I think he swapped in and modified the Corvette LS3 tune for the ECM. These (hopefully I've uploaded them properly) are the tunes in the car today. Again, any help is greatly appreciated. Gary
Taz, also agree regarding the misfire detection and plan on changing that back on next flash since it didn't help cure the problem anyway.