Hi everyone.

I have a 4l60e with 3 wires ISS and T42 24239926 controlling it.

Suddently, i lost the ISS signal to the TCM, Codes that pops up : p0741, p0717 with really harsh shifts.
Logs on HPT shows no ISS signal at all in any speed.

Tried to replace the TCM - No luck
Replaced harness - No luck
Dropped the Pan, spliced the V wire (DK/GRN) on the connector and connected the ISS Ground to the VB Bolt - Blows my Trans fuse in a fuse box.
I have checked the ISS itself with plug disconnected for shorts with a multimeter, no shorts were found.

What could be the issue? Is it possible to tune out this ISS or fix it without removing the trans?
Thanks!

2008 4.2 Trailblazer

This is how i found my connector when i first dissasembled it.

 

My understanding is that in the 07 and 08 the code can be tuned out and operation returned to normal , But I am no tuner. But have been told by tuners and individual's they have done it and can be done when placing earlier models without ISS in place of these. Again I am not a tuner and the best place to ask this would be the tuning section of the site.
The grounding thing it my understanding is a trick for the 2009 up when the ISS fails but I have not actually done it nor know anyone directly who have, But have seen it mentioned. Though I really do not see how it could work.
Now it is my understanding that in 2007 and 2008 the ISS was strictly a diagnostic tool and while it will set a check engine light it should not otherwise affect trans operation. So you may be dealing with more that one issue here. Again I am not a tuner and I am only going by reports from others who have either placed an earlier unit in these without ISS or had ISS failure, Each reported they had a code for the ISS but no other adverse operation.
Now in 2009 up the ISS is used operationally and can affect operation. This may also be true of aftermarket controllers that use it.
Again I am not tuner.
As for testing The ISS if I remember correctly it is a hall effect sensor so reading short or open pretty useless. Best I was able to get playing with one and an analog multimeter was a slight movement of the needle when passed over. But more than likely you have a failed sensor.
As for blowing fuse a hall effect sensor has a current passed through it which is interrupted by a magnetic pulse making a wave form of sorts.

Hope this helps but again I am no tuner and most of what I am saying is hearsay and reports from others, Not personal observations, Most of what you are asking would be best posted to the tuning section IMO.

Sorry I cannot be more help

 

Hi dear Frank and thanks for your reply!

In my case, it is a big part of torque management and somehow jerks with the TCC.
It detects slip on the TCC because the ISS has no signal, and commands way higher line pressure. Thats why 1-2 and 2-3 gears bangs on a super light throttle.
It has something to do with TCC Duty Cycle stuff.At least, thats what ive read on other forums.

Maybe this is complete BS but pros here will correct me.

And i will be more than thankfull if there is a simple fix and it will save me from pulling out my tranny

 

HERE is what I found in HP TUNERS FORUM
Changes to be made in tune to disable ISS
Trans Diag> DTC>P0716 and P0717 to no error reported.

Trans Diag>General>P0717 ISS Low to Disable.

Trans> General> ISS Fitted to Disable.

https://forum.hptuners.com/showthrea...l=1#post517601

 

I already did that. It doesnt help at all. Gears instantly bangs.
When you enable the ISS, the vehicle drives fine and soft for the first few miles. But after that, the TCM detects exessive slip in the torque converter and commands high line pressure.

 

Then I have no idea , But again I am no tuner, But have seen multiple post of people solving the issue even using non ISS trans in place of ISS units in 2007 and 2008.
I still wonder that you may have two separate issues but again I am no tuner, I would ask in the tuning section here and also the HP TUNERS forum. I also wonder if you could not just do a 2006 segment swap on the trans section but again I would ask in one of those places.

 

Yeah, this is a hard topic.
Lets see what Maroon and Vortec and Tranzman says about this. They are preety busy but i dont believe something in this forums can be left unsolved
Thanks for your feedback Frank!

Anyways, ISS creates problems where there shouldnt be any. So one day people will read about this.