redclay

I have a 2006 LS430 w/ 136K miles and after much research, I'm virtually certain it's experiencing a problem with the ECM deteriorating, which can result in very hard downshifting between 2nd and 1st gears as the car slows to a stop. The issue is well documented in this thread (and numerous others) and this article.

As a final question before I pull the ECM, I'm hoping someone can give me a little help with Techstream. When I bought the car a little over a year ago, I purchased Techstream so I could go over any trouble codes but unfortunately never had a chance to bone up on the program. I've successfully run a health check, but what I don't know is this: What trouble codes should I look for in terms of a shifting/transmission problem? And where in the readout would I find them (the ENGINE module perhaps)?

(Sorry for my total noob-ness on Techstream - I've never had a scanner or similar program before. And BTW, there *are* error codes on the health check but none related to this issue as far as I can tell.)

This particular ECM/hard-downshift problem is known for NOT throwing any codes, so I'm hoping to confirm that. I'd love to know any codes that could otherwise indicate the hard-downshift problem? I'm actually hoping NOT to find any, which would be consistent with the other well-documented cases... just want to be sure as reasonably possible before pulling the ECM and shipping it for repair.

If anyone can help, I would be MOST GRATEFUL!

LeX2K

A flaky ECU means the computer will not reliably set trouble codes so trying to diagnose based on that is chasing phantom codes.

redclay

Thanks for replying! So if the ECM *was* operating properly, where would transmission-related trouble codes show up in the Techstream Health Check report?

LeX2K

More accurately any code(s) set would be legitimate in the context of how the computer decides to set codes. I get the sense you want Techstream to definitively tell you if there is a problem with the transmission, that may or may not be the case.

redclay

Actually, it's the opposite. I *DON'T* want to see any transmission-related codes because that would be consistent with others' documentation of the same symptoms. My problem is I'm a complete novice with Techstream and don't know where in the readout to look for transmission-related codes in the first place.

As counterintuitive as it sounds, I just want to know where to look (and what to look for) in hopes of finding nothing (transmission-related anyway). Just trying to cover every base before sending the ECM off, which means I'll be without my car for a week or so.

LeX2K

Techstream is not hard to use you'll probably figure it out quickly. And if not watch a few vids on Youtube.

GM430

I have a 2006 and ran into the same problem - no diagnostic codes. I had the dealer send the ECU for repair - apparently the the board had solder failures and was fixed.
Dealer reinstalled the ECU and it is working fine.
You may want to look at the threads describing the ECU repair - there are are places like SIA electronics, where you can send the ECU for repair (not a recommendation!) https://siaelec.com/

Good Luck!

Peacebay

Techstream is great to have, but it won’t help you at all here. I thought I was missing something when my car had this issue, so I took it to the dealer master tech (also an LS enthusiast) and he couldn’t find any codes. ECU rebuild fixed the downshifting issue forever.

caverman

Can't help with the Techstream but you just need to get your ECU repaired. No need to go to a dealer or any mechanic for that matter. It's a super easy DIY and you can send it directly to where the mechanic probably would. Just did mine a few months back. You'll be without your car for about 10 - 14 days with the shipping, repair, and return shipping. I added some pictures to a DIY thread on the forum and you can get it done for $115.
https://www.ebay.com/itm/223971437477

redclay

Thanks so much, @caverman ! I actually did exactly what you recommended earlier today and it was simple. My ECM is now on its way to that same ebay vendor you linked to (best price I found). Beats the heck out of dropping $1500 on a new one from Lexus!

By the way, do you know if there's any advantage in reconnecting the battery before the ECM is reinstalled? I can't imagine a need considering the car won't start without the ECM (trickle power to some other passive electronics, maybe?) but the thought just occurred to me.

redclay

On its way for repair, @Peacebay . Thanks for your reply!

redclay

Thanks @GM430 ... ECM shipped out today.

caverman

I think I disconnected the battery before removing the ECM but honestly can't remember if I did 100%. It would probably be best to disconnect the battery and then reconnect after it's installed to be safe. Be prepared that they are going to tell you that you need to have your ECM re-flashed but I think they just say that to cover themselves. I didn't do anything other than install it once I got it back and it work perfectly right from the get go.

rrgone

Please update this thread when you get your ECM back and installed. Thanks.

redclay

Will do, @rrgone .