I hooked up the replacement backwards in my 1999 GS400.

I've seen other threads about this and I'm 99% sure that my current problem is the ECU.

I've got it out and I don't smell any smoke.

Is there a way to troubleshoot / diagnose the problem for sure before I spend $100s fixing it?

 

Your main fuse is probably blown.

 

Agreed^^^ your ECU is protected with a fuse. You couldn't harm it like that.

 

Thanks guys. I should have stated that we already replaced the main fuse. It was a BEAR to get to!

I didn't realize it was backward until I had connected the battery several times for a minute or longer each time. The horn blared solid the entire time, headlights and hazards were on solid while I tried locking and unlocking doors, turning the key in the ignition or attempted to start the car. Obviously none of the above worked.

Once we had a battery in correctly, it refused to start. NOTHING happens when I turn the key to "start".

Edit: After looking over my notes, the car cranks but won't start since replacing the main 120 amp fuse.

I'm getting most of the lights on the dash, but oddly, the clock in the dash is not lighting up.

The confusing thing is, I took the ECU apart and I don't see any damage. No burnt resistors, no bloated capacitors. Thus, the inclination to troubleshoot further.

Also: I used that exact video to figure out how to get to the main fuse! He's the Real MVP!!!

 

No worries, there's probably another blown fuse. Lexus won't let you damage the ECU. Someone in a similar thread had several blown fuses:

1. main 120Amp,
2. etcs fuse
3. am2 fuse
4. Radio no1 fuse
5. Dome 10a fuse
6. IGN fuse

Grab a test light and go through them one by one. You'll find it (or them as the case may be).

https://www.clublexus.com/forums/gs-...sequences.html

 

Thanks! I'll get on that.

 

Not trying to be a jerk but this a patently false statement. I am a Lexus tech and I have seen thousands of dollars worth of fried ECUs from people installing batteries backwards. Even worse is when people try to jump cars backwards!

Will

 

Can you include any positive suggestions for what this person can do beyond checking fuses?

 

I would check for continuity between the main fuse and the ECM. I am on my iPhone so I cannot look up the wiring diagram on TIS. Thus, I cannot provide the which pins/connectors to check. I suspect the ECM is fried - that is what usually happens when a battery is installed backwards.

Probably the best course or action is to check EVERY (not kidding) fuse in the fuse blocks. I have seen seemingly unrelated fuses cause very strange issues. Additionally, make sure you didn’t burn up any grounds or leave any grounds loose.

Sorry for the less than helpful response earlier - I was irritated with my wife when I posted it.

Will

 

According to several other guys at the shop, GSs don’t usually fry the ECM when the battery is installed backwards. I recommend rechecking all of your fuses.

 

My money's on the Lexus tech with first hand experience.

 

Thanks guys.

Today I hope to check the last fuses (haven't had a chance to check the fuse box in the driver's kickpanel yet).

I'm still cautiously optimistic about my chances of getting this going with just fuses, but Will's comments mirror the same sentiment from other experienced people I've spoken with.

 

Sorry for the late wrap-up on this, I've been driving the wheels off the car!

I hadn't found the fusebox in the driver's kickpanel before I started this thread. In my car, the cover (and all the codes printed on it for what circuit is what) is missing for this particular fusebox. But, there was ONE fuse blown. A 5 amp fuse.

The car started on the first try after replacing that 5 amp fuse!

THANK YOU to all of you who replied to this thread, you saved me days of time and HUNDREDS of dollars in cost which I was resigned to spending to get the ECU repaired.

THANK YOU THANK YOU THANK YOU!!!!!

 

That's good news! Glad you got it worked out.

 

Interesting conflict of information here. In my experience as a tech, fuses always blow before ECU's.. just saying. But I guess some unicorns must happen at the Lexus dealership.. I've replaced dozens of main fuses and primary circuit fuses for backwards battery installs/ jumps. Never an ECU. Glad for the OP that it was just a fuse.