I need help! I live in Florida. I have a 92 sc300 that has had all kinds of problems. Long story short we bypassed the ECU and it was running fine. Now today it just won't start. It's showing a picture of the battery and I just bought a new one last week! As you can probably tell I'm a girl who knows nothing other than what I've read over the last 2 weeks. We replaced the positioning sensor, new plugs, idle control valve. The lexus dealer said it was the ecu, so we bypassed it for now..what could be wrong now?

 

So rather than spend a couple of bucks on a used ECU and make the car go back to normal, you opted to magically bypass it.

Get an ECU and eliminate whatever rig job on wiring you did.

 

Check the Alternator

 

it likely is failing ECU capacitors, but you can fix it for $10 in parts if you are a pro solderer - otherwise, it is gonna be a little pricey to have someone do it, but a lot less than $1000 for a Lexus reman ECU if one is even available.

'92 SC300 is one of the more difficult ones to rebuilt, but can be done if you are patient and meticulous with small delicate work.


the alternator is another common failure point, due to leaking power steering fluid which kills them, and if you don't fix the power steering leaks, it will kill the new alternator in a few months!

a 3rd thing is the replaceable positive (+) battery terminal (about $15 at any Toyota dealership) - get the real Toyota one, not Autozone, NAPA, etc. - hidden corrosion invades under the bolt (I am speaking about an area a few inches down at the cable, not at the battery post)