Transmission not always shifting up from second to third gears?

PIETJE PUK

MEMBER
2005 CADILLAC ESCALADE
6.0L
V8
4WD
AUTOMATIC
100,000 MILES

The transmission (4L65E) is only shifting from second to third if I let go of the throttle. Then it will go to third and fourth. If I do not let go of the throttle, it will increase revs to 5,000 - 6000 RPMs without shifting up and of course speed will not further increase after that. Let the throttle go, and it will shift, and I can accelerate to any speed I want. Third to fourth goes smooth. There seems to be no slip at all. It seems the computer just does not give the signal to shift up to the transmission. I replaced the output speed sensor. It improved a little. Cabling of OSS is good.

I connected ODBII and I can see that the computer indeed does not give the order to shift to third, unless I let go of the throttle. Gear ratio is stable in each gear, no slip. But the rpm's that the indicator and ODBII give seem to be correct. So that should show a good Input speed sensor, right? Or is that different?

There are no fault codes. Well, there are, but not related: C0196 (yaw rate sensor) and P0496 (solenoid valve).

What can it be?

1 Reply

KEN L

MASTER CERTIFIED MECHANIC
47,643 POSTS

Hello,

It sounds like you may have partially clogged catalytic converters lowering the vacuum and air into the engine which makes the computer think you are going up a steep hill. Here is a guide that can help us confirm the failure. Just loosen the header pipe bolts to see if the release in pressure make the transmission shift.

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Please let us know what you find. We are interested to see what it is.

Cheers, Ken