Thread: PO717 on 4T65e-HD - Stumped

Hey Folks,

I'm posting this because I am stumped and could use some advice. I've spent the last 24 hours reading and working on this with no fix.

Symptoms:
Loss of 4th, and intermittently 3rd gear. Shifts are firm, even when it isn't in performance shift mode.

OBDII Code:

P0717 No/Low Input/Turbine speed sensor signal.

Actions Thus Far:
As I have read, the possible issue would be the ISS itself, or the wiring between the 20 pin connector and the PCM. I initially unhooked the PCM harness and the 20 pin connector and checked the continuity of the two circuits. Continuity confirmed. Secondly, I plugged the 20 pin connector back in the transmission, and checked the resistance between the two circuits via the PCM harness. I registered 1023 ohms, which was within spec from my understanding, also considering the car was driven about an hour or so before (100* heat). The 20 Pin connector looks to be in good shape, with all connectors showing and no corrosion (never had the 20 pin connector off before). Have not yet sprayed it with contact cleaner.

Vehicle:
-98 Buick Regal GS ~250,000kms
-Intense S1X Cam
-3.25" pulley
-DHP PCM
-TOG Headers
-CAI
-3" Cat back

I've had the car since new, and has some mild mods - this is my 4th motor. I've always done regular maintenance on the transmission, including a fluid and filter change about a month ago, with regular amount of metal on the magnet, fluid not burnt. I service the transmission every year. The transmission has never slipped, and always had good firm shifts up until this issue.

Despite my testing with the continuity of the wiring to the PCM harness, and the appropriate resistance within the ISS, does anyone have any other ideas?

Thanks in advance!

Additional Info:

During city driving, the loss of 3rd occurs once the transmission has reached about 180*. Temps below, third is functional with TCC locking.

I'm certain I've read the the ISS is internal, and requires the transmission to be opened via the drivers side access panel - i.e. a bit of work?

It had been beaten on in its earlier years, but I'm sure it would catch up with it. So by following those instructions, I should be able to tell if it is the drive gear based on missing/ground down teeth? I can handle most mechanics of the car, but the transmission is something I've never delt with. I'll have to call in a pro to help me. Thanks for your info, and I'll be certain to follow your other post on hopefully fixing this.

Also, no noises at all, and is still driveable.

Well I appreciate your assistance, and all your other posts and information I used to get this far. I'll be getting in touch with my transmission tech friend, and take it from there.