Input Speed Sensor

JWGROFF05

MEMBER
1999 CADILLAC DEVILLE
V8
FWD
AUTOMATIC
187,878 MILES

I got a p0717 code from my pcm earlier today. Now that I read this code as the Input speed sensor circuit no signal. I have underostood that you can have a bad connector, faulty wiring or the sensor which is bad itself inside the transmission. The car shifts hard every once in a blue moon and then most of the time it doesnt. Once its warm it doesnt shift hard at all. I was wondering if you could help me further diagnos this problem and if so how would you replace it inside the tranny to get to it?

1 Reply

FACTORYJACK

MECHANIC
4,159 POSTS

If you had a scan tool that read PCM data, you could see if the ISS is inputting a signal. If this code is current, and a hard fault, then you may be able to diagnose it by checking resistance. You can measure resistance from pins 5 and 6 at the PCM C1 connector(blue), the wire colors are DK Blue/WHT and RED/WHT. You can also check at the transmission 20-way connector pins V and S. On the transmission side of the 20 way connector, the wire colors will be DK GRN(v) and BLK(s). Resistance of the sensor will be 1260 to 1540 at 20 deg C, more if warmer. The hard shift may be default line pressure increase in response to the fault. Earlier(94-95) 4T80E's had some issues with the sensors, and internal harnesses, but not many on later. That is not saying it is not a sensor. If it is an intermittent fault, it may be difficult to diagnose. To replace it, you almost need to have the transmission removed, but you can lower the powertrain far enough on one side to remove the side pan and channel plate. The latter procedure is more difficult, and the potential for creating some other problems is higher.