azjaybird

Hi Guys, I'm new to this forum and would appreciate any help. I just purchased a used 2007 is250 RWD and got what I thought was a pretty good deal at an auction (price wise). Bought the car without being able to drive it and there's no return policy, so taking the car back is not an option. The car starts, runs and shifts through the gears just fine, however, when I'm slowing down for a traffic light or slowing down to a stop, say 40 mph or less, the car downshifts hard, seems like it's shifting from 4th to 2nd or something like that, or 3rd to 1st gear, just a hard downshift. It only seems to happen under about 30 or 40mph. It's never happened to me on the highway or at higher speeds, such as shifting from 6th to 5th or 5th to 4th, etc.

I did some digging around on the internet and saw quite a bit of people were having this similar issue and they fixed the problem by having their ECU rebuilt or reprogrammed. So the other day I pulled the ECU out of the car and it had the name of the car dealership I purchased the car from, so it was pretty safe to say they had the same idea of reprogramming the ECU. I figured instead of wasting anymore time and money I would just call the dealer and ask them what they had tried already.

The dealer told me he started out by putting a used transmission in the car and it had the same downshift problem. He then put a second used transmission in the car and had the same problem again. This is when he sent the ECU out to get reprogrammed. Got the ECU back, put it in the car and still same problem. He took the car to Lexus and they told him it needs a new transmission.

It just sounds crazy to me that this is essentially the 3rd transmission in this car and it's having the exact same problem. I'm wondering if there's anything else in the car that's electronic other than the ECU that could be making the transmission malfunction like this? It just seems like too much of a coincidence that 3 transmissions could be bad, or is that wishful thinking? Anyone have this problem and have some ideas? My absolute last resort is putting another transmission in the car, I'm hoping there's something else I can try.....Thanks! Oh, and the car has 139k miles on it, I'm not sure how many miles this current trans has on it, I'm guessing 100k+ as well.

primavera

It can be difficult to get the fluid level correct as most non Toyota/Lexus techs have no idea how critical it is. If I were in your shoes I would verify the fluid level first and foremost to rule out the possibility of that causing any issue...


Maybe try to contact these guys?

http://siaelec.com/
http://www.transgo.com/index.html


Failing alternators often cause transmission shifting issues since automatic transmissions are computer controlled, the computer requires a minimum voltage to operate. If your charging system falls below the minimum voltage requirement, the transmission will not operate correctly and will often go into limp mode. I suggest load test your alternator and battery, check for loose alternator belt, tensioner, pulleys, corrosion on battery and connectors.

I have read somewhere that if the cat converter is clogged up, the oxygen sensor will trigger error code in the computer that causes the transmission to go into limp mode to avoid overheating and potentially causing damage to the transmission.

https://itstillruns.com/can-alternat...s-7757568.html

2013FSport

iTrader: (2)

^^^ +5 on above input.

If you could invest in an OBD wifi or bluetooth device (elm 327 $30) and either OBD Fusion or Torque pro App you could log some data. The trans ecu (TCU) and engine ECU relay on each other to make a lot of choice. An engine low on vacuum implies to the system it is under load and can for this reason make harsh abrupt shifts.

So rather than trying to fix something that isn't broke (vacuum leak or poor running engine), lets gather some data and eliminate suspects.

Can you clarify if it was ECU or TCU that was reprogrammed?

Mrfix

I guess you know why the car was at auction now. Anyway, I would check the wiring from the ECU and everything in between. If that all checks out I would imagine that the ECU was not reprogrammed correctly because having the same issue after all that is to coincidental.

Gville350

iTrader: (10)

Was it mentioned whether or not that the T/C was replaced along with the trans each time? Though I've never had to myself, I've read that you're supposed to keep the trans and T/C matched as a matched pair.

Chinorx3

Well I have Total of 3 is 250 , and 1 have tranny issues . I’ve owned Lexus for about 15 years and never had an issue on any of my cars . I own a 2016 Lexus GS 350 f sport . I believe in the brand but why I hVe a trnamission issues still gets me mad .