Downshift Clunk

[Dark Horse]

Greetings All,

Just today while out doing errands, coming to a stop, when the transmission downshifts to second gear and first gear while braking I'm feeling a very noticeable clunk. Upshifts are smooth and normal. Has anyone experienced such, and can they share the remedy please? This is on my 2005 LS430 with 164K. I'm attempting to establish if this an external joint (as in universal) issue, or internal transmission issue. Any input would be most appreciated.

[AdeelN]

i have exactly the same issue, took it to the transmission shop and they coulden't fix it

[Dark Horse]

It's not a transmission problem that is causing this to happen. I researched this issue and figured out what the issue was. The problem is the E.C.M.. There was an extended warranty on this part because of this known Lexus issue (10 years after the factory).

My car was older, so I had my E.C.M. repaired. I had it removed and then sent to a shop in TX. After all my research, I found this company to be most reputable, and they did a great job.

There may be a company close to you that can do this. If not, message me and I'll give you the info on the company I used.

[RX400h]

Quote

This seems to be a known issue with some Lexus models, including the LS430¹². Here are a few possibilities based on similar cases:

1. Transmission Solenoid: The shift solenoid is internal to the transmission. To access it, the transmission pan and valve body would need to be removed. A failed solenoid could cause rough downshifts.

2. ECU Issue: Some owners have reported that a replacement ECU or a software update fixed the issue. In one case, an ECU repair costing around $200 fixed a similar issue².

3. Driveshaft Bushings: In some cases, the issue turned out to be with the bushings in the driveshaft.

4. Transmission Replacement: In the worst-case scenario, some mechanics have suggested replacing the transmission altogether. However, this is a costly service and should be considered as a last resort.