2004 Lexus GX 470 transmission slams

my transmission slams when idling while in drive

I’m not quite sure what the transmission “slamming” might mean, but the first thing that I would have my mechanic check would be the transmission mounts, as well as the motor mounts.

Is the Check Engine light on?


Yes, check engine light is on

And the transmission fluid…

You need to get the codes read to see if any are related to the transmission.

From what you describe, it sounds like the transmission is neutralizing and then going back into gear.


The 2004 is the only closed transmission, you can’t check the fluid level. I did get it flushed and refilled about 5 years ago. It’s suppose to not need filling for 100,000.

While it probably isn’t a simple thing to do on your driveway, a shop can check it for you. Shouldn’t cost much, if all they do is check the tranny’s fill level. After reading out all the diagnostic codes, that’s where I’d start w/this problem.

Failing engine or transmission mounts would be unusual on this vehicle. What is the frequency of the “slamming”? Once a second, once every 5 seconds?

The fault codes may show that the transmission has failed.