soleil14

Hello,
I bought a 1999 Lexus LS400 1 and a haft year ago. It was very reliable and I never had a problem with it.
I got a problem with the wiper control. I replaced the MPX body control to fix the problem. After that my remote key stop working. I ignored the problem and keep using the car. Two days ago, a technician reprogram my remote key and make it work again. (doors, trunk, locks, all worked perfectly). I started my car and was very happy to drive home. In the evening, when I got in the car, the car cranked but didn't start.
Is there any chance that the immobiliser system is causing problem?
When I put the key in, the security light turns off as usual.
I checked all relays and the battery and all work well. Except for the fuel pump relay that not powered when my key is in postion On. But I think this is normal.
I suspect that immobiliser system or my ECM is causing problem because my car worked very well before my remote key is reprogammed. I don't know what to do now. I live in Vietnam and it's hard to find a mechanic to fix my LS400.
I intend to replace a new ECM + key and I found this link on ebay:
http://www.ebay.com/itm/191737878103
However, I also found that there are variuos part number of the ECM for the North American market:
I haven't check what is the part number of my ECM .Kindly let me know whether the ECM part number 89661-50531 can replace the ECM part number 89661-50502 or not?
Many thanks!

RA40

iTrader: (6)

Welcome to Club Lexus.

My thought before putting money into this is to see if you can read an error code. This may not be an ECM issue. Being able to read any codes or communicate with the reader will let us know if the ECM is working at least.

I see you found Yamae's list What country was your LS400 exported for? Definitely having your ECM part # will help for checking cross compatibility. Is yours left or right hand drive?

soleil14

I live in Vietnam but my LS400 is for US market. Vin number : JT8BH28F6X0158941

Yamae

Did you check the fuse "EFI 10A"?

If it's OK, I need to confirm a few more items before I give you additional ideas.

Was it you who replaced the MPX body control computer unit?
Was it done using a wrist strap to avoid the static discharge?
Did you do it after the battery terminal is removed and waited at least a few minutes to discharge capacitors fully?

What I worry about is the damage caused by the static discharge. The MPX body control computer unit communicates with the engine ECU via the signal line named KSW (Unlock Warning Switch). The line is rather weak against the static discharge.

soleil14

I checked EFI 10A relay and it has power when my key is in On position.
I changed the MPX body control by myself. I just take the old one out and put the new one in. But it was two months ago and my car worked pecfectly after that, except for the remote key. 3 days ago, a technician reprogrammed my remote key and make it work. Then, I can start the car and drive home. But in the evening of the same day, the car didn't start.

Yamae

I need to get your answer for the 2nd and 3rd questions.

soleil14

I did not use a wrist strap and I did not remove the battery. But it was 2 month ago when I replaced the MPX body control and the car run well after that.

Yamae

So you did what should not be done. Sorry to say but you must be not familiar to deal with computer controlled units. There is a possibility that the partial damage 2 months ago was fully damaged now. The signal lines use C-MOS logics and there often happen minor partial damages when the minor static discharge/unwanted voltage is applied and later on it fails completely by some newer triggers.

As I wrote before, the MPX body control computer unit is connected to the engine ECU and it is dangerous to remove/install those without disconnecting the power source. Those are always supplied the 12V DC from the battery and making a low voltage logic DC supply which has big capacitors. Those capacitors hold electrons some time after the battery is disconnected. That's why you have to wait till the capacitors are mostly discharged.

There is also another possibility which is very simple. I mean a connection issue. The remote key system and the immobilizer are controlled by separate logic circuits but there are some common part. The low voltage DC circuit and the bus signal line are so. There may be some connection or communication issue there caused by your job or a mechanic job.

It may be an idea to replace the ECU seeing the ID number but you have to rewrite the EEPROM inside using a special equipment which is only owned by authorized dealers or agents.

I'd check the connection issue and the low voltage DC supply circuit first. I'd also check signals between those 2 using an oscilloscope.

PureDrifter

iTrader: (10)

It's possible the ECU was damaged but it could be a security related issue, but without a scanner that can tap into the toyota-specific codes (basically something running Toyota TechStream) you can't tell if the security is what's keeping the car from starting.

Have you tried a different key per chance?

fixmiester

I had similar symptoms awhile back with my '99, so we tried my other key, and it worked! Turned out to be that the screw that holds both halves of the key together had come out, and the wireless module had fallen out, onto the floormat, without us even noticing it. That put the module too far away from the key/security sensor, and kept the car from starting, even though it cranked fine. Sure am glad that I didn't lose that module in a parking lot before trying to unlock the car. Second keys can be a life saver.

soleil14

Sorry for disturbing all of you. I found the problem. The failed fuel pump caused the problem.
It just happened after the key is reprogrammed and make me thing wrong.
Thanks for all your helps!

dicer

Yamae, wouldn't just touching everything metal in the car be like having a wrist strap on? I use one when handling the circuit boards, I didn't think you needed to worry about it if you had the ecu in the metal containment box its all in.