LexInFL

LS430 2005 177K miles.

Problem:

2005 LS430 Downshifts from 2 to 1st too early, causing jerk/jolt/clunk/.

Lexus dealer diagnosed that the problem is ECM and quoted me $2272 ($1800 parts + labor + tax). It seems little expansive to me. They said there are no TSB to fix this issue for 2005 model.

Has anybody send out their ECM/ECU for repair to some shop listed online and was it successful?

Can you buy a ECM from ebay and reprogram it yourself or can only be done by the Lexus dealer?

Any help would be greatly appreciated

Thanks

05ls430518

iTrader: (1)

The ecm has to match the numerous immobilzers in the car which needs to match the chip in the key if they do not match the car will not start it part of the antitheft system

bradland

Are you asking about the Powertrain Control Module PCM AKA Transmission Control Module TCM ?
Or the main ECU/ECM for the entire car ?

LexInFL

Thanks for all the replies.
Bradland, Sorry I didn't realize that the gear shifting was controlled by the TCM. Where is that located?
I was reading some of the other threads and most members said that this type of problem is normally in the ECM (Engine Control Model)

My other question was:
Can you buy a ECM from ebay and reprogram it yourself or can only be done by the Lexus dealer?

k7q

iTrader: (37)

I paid $1800 for my ecu at the dealers. Part and labor. They did the tsb flash and didn't help, so they said it was the ECU. Now it drives fine.

05ls430518

iTrader: (1)

It can only be done by a dealer, your immobilzers need to match your key and ecu, in order for your car to start.

LEX ES300

I get so confused with all the names ECU, ECM, TCM etc. All i know is that i replaced the ECU - the one in the engine bay (not the one for the whole car that is inside the car) and i did not have to do much to get it working i did it myself. I got it from a wreckers because i was trying to fix a trans issue that i still have where i have absolutely no engine braking at all going downhills and one possible fix was replace the ecu. I replaced it and no luck, i still have no engine braking. Anyway back to the ecu i just swapped it over and then the engine wont start at first because the security kicks in, but then you just calibrate it to your vehicle by connecting a few specific points at the obd port by using a paper clip, then leave car with the ignition in the on position for about 5 minutes then the new ecu will have calibrated and the car will start no problems. You would only have security smart key issues if you replace the main ecu for the whole car. I am still running my 04 ls430 with the replaced ecu with no problems other than it didnt fix what i was hoping it would.

LexInFL

Thanks. I assume the same goes for 2005 LS430.

LexInFL

I took out the ECM out and sent it off for "repair" to SIA Electronics. Lets see what happens. I will update the thread when I get it back.
BTW I don't know why the Lexus dealer wants so much money for labor. it took me 10 minutes to pull it out. Also It looks the online price for a new unit is $1320.

part # 89661-50781, COMPUTER, ENGINE CONTROL. It is sometimes referred to as Lexus Engine Control Module (ECM) or Engine Control Unit (ECU).
Still not sure what and where the TCM is located.

LEX ES300

No problems, keep us updated on the progress!

RXGS

iTrader: (2)

Many guys on GS forum have done this SIA rebuild with great success. Different car, but same transmission I believe

YODAONE

Recently solved downshift cogging on 1999 LS400 by replacing TPS (throttle position sensor).

With 177,000 miles then your TPS and, or, Pedal Position Sensor is suspect.

https://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/878565-1998-2000-ls400-improved-transmission-shifting.html

Worth pursuing before replacing your $$$ ECU.

TPS is about $100 (uninstalled and not indexxed or calibrated)

Pedal Position Sensor is $465.79.

TPS is #89452....
Pedal position sensor is 78120G

LexInFL

Thank you all for your input.

YODAONE - Great diagrams, they really do help finding things. I had to guess where the ECU when I was looking for it.
Unfortunately I have already sent off the ECU but if that does not fix the issue then I will look into the TPS and the Pedal Position Sensor.

YODAONE

Before you replace ECU, replace TPS.and determine difference..

After 177,000 miles it is a contributing factor.

Surprised dealer did not verify...it is a variable resistor and prone to wear.

Find a second mechanic for separate opinion.

LexInFL

I would but I don't have my ECU, it is with SIA Electronics.
I called them today and they said the turn around time is 4 days even though the website says 2 days. Not happy about that.
Finding a good mechanic is hard I had taken it to two other shops and they told me it was the Transmission.