ychen

I finally fixed the engine (with an replacement). Also fixed the P1600 (bad trace on the ECU, fixed the capacitors as well). I notice a strange thing on the idle. Normally when turning on the AC or headlights, the car's idle should go up, but mine doesn't. Also the car dies when making a turn. Does this sounds like a vacuum or EUC issue? Sometime it dies when accelerating. Thanks in advance.

ychen

More info discovered today. The car (my 97 LS400) was ready to do the state inspection after sitting in the garage for over 2 years. I drained the gas from gas tank and filled up today and drove 20 miles. I plugged in my scanner and it said it was ready for the inspection. When the inspector pulled the car from the paring lot, It died on the road and the car failed to restart. Finally after banging the gas tank, It started, guess what, the inspection computer said the car was not ready. I immediately checked with my scanner, sure enough, not ready. I think somehow the ECU reset itself. I would like to reiterate that I have replaced 6 capacitors for (95-97). fixed the P1600 (note more P1600 code). From the mechanic who replaced the engine the fuel pump was weak, That's another issue. I often need to bang the gas tank to start the car. Now it seems that ECU is still not good (resetting by itself). I have a spare ECU, but I can't test it due to the immobilizer on 97 LS400. Is there a way to bypass the immobilizer so that I could test with another ECU? This is a pain (for 1997+). Any thoughts from ECU experts Yamae and or LScowboyLS or other experts? As always, Thank you in advance.

Yamae

There is no limit to excellence and there's a way.

But the only thing I can say is that it's not simple. You need to make an equipment which makes it possible to read the stored code first. Then there are several more steps to do. .......

I don't think average DIYers can do those. Only a genius or some specially trained personnel with equipments can unlock it.

ychen

Thank you sir for your quick response. I was hoping something similar to this I guess my best option is to have the dealer reprogram the spare ECU.

Yamae

Regarding the idling up, check the voltage change of the pin #15 at the ECU connector A which has totally 28pins.

ychen

Yamae, thank you for your suggestion on the idling up. I concluded that the ECU is bad since the car cuts out in the middle of the road (with low speed) and erased the OBD II info. I am right? Can a used ECU (from another 97 LS400) be reprogrammed to work with my 97 LS400 (I heard some ECU cannot be reprogrammed)? Thanks again.

Yamae

You'd better to check the ID number again before rewriting the data. As long as the ID is the same and the code is matched, it should be OK to work. But remember that the spare ECU has good capacitors. 20 years are long enough to fail for those QAS capacitors. You can't judge the healthiness by your eyes, you know.

ychen

The current ECU is 89661-50340. The spare one is 89661-50431. I already changed the capacitors on the spare one. It seems the spare is newer.

Yamae

Wait!
89661-50431 is only for an earlier VVT engine. Is your engine a VVT one?

ychen

I doubt it. Mine is 97. According to http://www.lexuspartsnow.com/parts/l...661-50430.html

Both 89661-50430 & 89661-50431 fit 97 LS400. It seems late 97 and early 98 models both used 89661-50431. Anyway, I was told that mine spare one 89661-50431 was from a 97 model.

ychen

Sorry, my bad. The current one is 89661-50340. The spare one is 89661-50341.

plexus914

@ychen

On 97 model keys are programmed to the immobilizer box (Immo Box 1 - behind glove box) and not to the ECU. Have you tried your spare ECU yet?

ychen

Thanks, plexus914. That's good info. I just went to Lexus dealer this morning, they said they could not reflash the ECU, which maybe true. The service manager was trying to convince me that 97 LS400 didn't have a security chip. LOL. So they need to refresh the immobilizer box in stead of the ECU cause they could not reflash the ECU. I am amazed that the dealer doesn't know this. The service manager told me the mechanic has 30+ years of experience.

ychen

This doesn't sound very promising. I guess I need to be prepared that no one is able or willing to reflash the used ECU. Is there any way to fix or test the current ECU? I am at a loss that the Lexus dealer doesn't know how to fix this. The car will die at least once everything time I drive it, usually when it warms up and at low speed. I am going to try to call another Lexus dealer. Thanks.

ychen

@plexus914, I tried with the new computer, the car won't start. I called the Lexus dealer today again, they want to diagnose it first.