Over the past week I had symptoms on my 93 LS400 that seemed to indicate leaking caps on the ECU. It would lose power while driving, check engine light would come on, then there would be no codes once I checked them. I was in the process of trying to locate a replacement ECU or getting it rebuilt.

The car was running fine Wednesday morning then when I pulled into my parking space and turned off the key, it has not regained consciousness. When I turn the key to start, I get nothing - no clicks, dash lights, or interior lights. Does not even try to turnover. Same for the the accessory position. The only hint that it has electricity is the door chime sound when I put the key in, but it won't even lower the radio power antenna or lock/unlock the doors.

The battery shows 12.7 volts with no corrosion and is only about one year old. I tried tapping on the various relays under the hood, thinking one might be stuck. No such luck.

Did the ECU finally bite the bullet completely, or is this an indication of something else? It's as if the battery wasn't even in the car.

 

All symptoms indicate a bad battery cable.

 

Agreed or a bad battery or a battery than is not being charged. A bad ECU shouldn't prevent all your dash lights from coming on brightly. If your ECU is on the way out, when you turn the ignition on, you probably wont see the check engine light illuminated when the car does the bulb check.

 

Thanks for the feedback guys. Looks like you were spot on.

I went out during lunch and was able to crank the car with a pair of jumper cables connected to another vehicle. It fired right up. After running for a few minutes we turned it off, disconnected the cables, and tried to restart on the car's battery. Completely dead. Looks like the dead (or non-charging) battery was the culprit.

Only 11 months old. Taking it back to NAPA for analysis in a few hours.

 

Make sure your battery cables are not loose. Something as simple as loose cables can cause the issue you are having. If you try to move your cables, they should not budge on the battery post.

 

why has nobody mentioned the alternator?

 

yeah, could be a bad alt that killed it. if not, it may be bad now from running with a dead battery.

 

As PD mentioned, have the alternator checked but if it is dead, you will get the waring lights on the dash indicating so: brake, battery and CEL. Don't let the car run too much on just the battery...draining it in this type of fashion will shorten its longevity.

 

12.6 volts is a perfect battery....i dont suspect the alternator but maybe a bad cable. there is an off chance the battery is reading good volts but not holding the charge under load.

 

Had same issue on my 95. Turned out the battery was weak and caused the alt to work overtime which was it's demise. New battery and alt and it runs perfectly. Since you are getting new battery I would have the alt checked at your local parts store just to be safe. Good idea to check the cables as Chin suggested. Good luck.