A Few weeks ago, after getting back from a long plane trip and leaving my car overnight in a parking lot, my CAT light or exhaust overheating light came on. It was a bit concerned since I had to make a 2 hour trip back to my house from the airport, but the car worked fine and chugged along fine. 3 days go by and I get into my car to start it up and *ticktickticktick* the battery had died. Ticked off, I had to ask someone for a ride to work and back. After I jump the car, the car runs fine and receives adequate charge for the whole day but, overnight, the car doesn't crank and I have to keep jumping it. Reading up on the forums I found out that the CAT light can come on if my alternator is going bad. Is this accurate? I did not check any fuses yet...

 

I'd rather think it's an ECU capacitor issue or this. The English translation can be seen here although some expressions are strange.

 

Hello Yamae,

Regarding the ignition coil link, I'm not sensing any loss of power from the engine, or that my engine is misfiring at all, so it could just be the infamous ECU capacitor issue. I'll do some more research and update you. Thank you.

 

A bit of an update to this issue:

I received my rebuilt ecu today and re-installed it into the vehicle. I had to jump the car, since it had been sitting for 2 weeks, and let the ECM get re-acclimated to the car and it started right up no problems. I even drove it around and it felt like a brand new engine and car! Though, I still have the Catalyst/exhaust temperature warning light still on my dash. I have a feeling that it's more an electrical problem, so tomorrow I will clean the battery terminals, check the voltage drop on the alternator, and see if the car is grounded properly. I will update this thread tomorrow.

 

Thanks for the update. So those capacitors are not related to the CAT light issue but your engine runs far better than before. That is quite common among old LS400s.

I recently had a chance to fix a CAT light problem on an old Honda car. I found that it was caused by the temperature sensor attached to the exhaust pipe. It showed almost no change of the resistance value when heated or cooled. Replacing the sensor fixed the problem. I worry that your sensor is something like this Honda car. I suggest you to measure the resistance of your LS400's sensor. Does it change the value when heated up and cooled down?

 

Hi again Yamae,

I did not measure the voltage drop between the sensor yet, as I am not sure where it is, but I did come across a parasitic drain coming from the EFI fuse. The EFI fuse was drawing 4.3mV or around 1.3 amps. This I think is causing my car's battery to drain within 6-7 hours. I pulled the fuse out and it seemed to keep my battery from discharging. I am now seeing if it may be an ignition coil issue.

 

Hello I have the same problem , can you give more update on your case pls

 

ggiahuy,
I had to replace the ECU with a similar jdm-spec Toyota celsior ECU from Japan. I suspect that the ECU shorted out upon crank and caused some component dealing with communicating to the ECU about the CAT that routes through the EFI relay to stay on even when the car was off. I did not have time nor the knowledge to fix this, so I just purchased a sourced ECU.

Hope this helps.