Good Morning clublexus members,
I've had my 99 LS400 for about two years now, bought her at 145,000 miles and now have around 166,000. Since my ownership I've done a significant amount of work on it to maintain a pristine daily driver, and probably should have contributed more to the forums but have limited myself to lurking for the most part. While I've taken care of most of the mechanical issues, I recently started experiencing some strange electrical problems on an intermittent basis.

It all started about 6 months ago while at the gas station: after getting gas, I put in the key, and nothing happens. No dash lights, no chime, no steering wheel movement, and when turning the key to start, absolutely nothing happens. I check the battery voltage and it's good, so I pull the negative terminal, wait a few minutes to reset the ECU, put it back and it goes back to working like nothing ever happened.

Fast forward a couple of weeks ago and coming back from work, in my office parking lot, the battery is just suddenly dead. It's a 1 year old battery that I put on after replacing the power steering pump and alternator (original one got fried from a PS leak) and had shown no signs of trouble earlier that morning. I Jump it, check charging voltage, it's good, but the battery doesn't take charge: after driving it around for an hour it's still at 10V. I take it to Toyota to run an electrical diagnostic and everything comes back clean, they said the battery was bad. Strange for a battery to go bad so quickly but I take their word for it since there are no other signs.

Now yesterday, after getting it washed, I got to start the car and it starts but the gauge cluster is completely dead. No lights, no needles, as if the car were off. AC and Radio worked perfectly. Again ECU reset via disconnecting the negative battery terminal fixed the issue. After this reset though, the trip meters were reset to 0 and the odometer is now reading 6640 miles instead of 166640, which will require a lot of explaining to do if it can't be brought back.

What could be going on here? It seems to be pointing to an ECU problem but I have no idea how to proceed. When talking to a specialist about preventatively replacing the ECU capacitors a few months after getting the car, they told me that 98+ models weren't affected. Could this be an early warning sign of leaky ECU capacitors or is there something else that might be going on?

Thanks in advance for your help!

 

Before I put some more thought into these issues I'll just say that just because the 98+ cars don't commonly have the leaking capacitor issues as the older cars doesn't rule out an ECM problem. Powertrain computers go out all the time on every type of vehicle.

i'm not sure how intertwined the cluster is with the rest of the car on the 98-00 cars but I've seen clusters call issues all over the car if they're bad. Your cluster doesn't seem to be doing too hot. At least on the 95-97 cars the ODO info is stored in the cluster itself. The mileage changed on the ODO is pointing to you cluster having a problem but it may not be your only problem.

Has the car been hit by lightning by chance lately?

 

No, I don't think it's ever been hit by lightning. In fact, it's strange that I can't seem to recall any specific event that triggered these strange behaviors, they just seem to pop up occasionally after long intervals without any warning signs. On the Lexus reddit a user mentioned he had similar intermittent ECU problems and traced it down to water accumulation in the trunk due to the drain plugs being clogged, and that was causing some electrical connectors to be underwater. He had the additional symptom of blowing the ECU fuse though. My fuses are fine but the fact that a car wash triggered the most recent event is suspicious, I'll definitely check the trunk for water later today.

 

After washing car?

Check moonroof drains for blockage...

If rubber weather seal on moonroof is tired (or needs refreshing with Shin Etsu grease) or drains plugged then water goes over top of moonroof drain gutter, over headliner and down the winshield pillar, dousing several large connectors in the right footwell area of passenger side that connect with the body ECU.

Check under floormat and or lift carpet and see if wet.

 

I had most of the same symptoms as the starter on the 2000 LS400 I used to have began to fail at about the same mileage. Have your starter tested for excess voltage draw.

 

Interesting, any way to test it without removing it from the car? I'd only like to remove the intake plenum if I absolutely have to

 

It isn't necessary to remove anything. Do a google search for how to test a starter it but you'll need the proper equipment, understand how to use it and have the specifications for the starter. I suggest having a pro do it since a pro has the equipment and can do it in a few minutes.

My 2000 LS400 had all the symptoms your 99 has except for the odometer resetting. A new starter solved everything and I drove the car another 15,000 miles or so until I sold it at 180,000 miles in 2014.

Edit: I should have said: have it tested for excess amp draw

 

I agree with Jim, get ready for a starter job.... and it is probably just the solenoid contacts, but a lot of folks replace the starter after getting into the cavity.. post us...

 

I worry about that you have experienced the slow voltage drop or the jump start.
Judging from the symptom, either the EEPROM, the micro processor or the power down reset IC in the cluster unit is not working right. Your type of problem happens when the power down reset is not properly done. When the Vcc for the cluster unit drops about 10%, the power down reset IC works and makes a reset pulse. The micro processor starts the closing job given that pulse. When the closing job is not done, strayed electrons in the EEPROM may cause your type of problem.

If your problem were caused by the reset IC not making a good reset pulse due to the slow voltage drop or unusual voltage swings caused by the jump start or others, it would be probably fixed doing these steps below.

1, Connect a well charged battery.
2, Turn the ignition key to the on/run position until the VSC/traction light goes off. It takes about 20 seconds. Do not start the engine while this.
3, Turn off the ignition key and remove it.
4, Disconnect the battery.
5, Wait for 1 whole day or more (24 hours or more) to erase the strayed electrons.
6, Connect the battery and turn the key to on/run position and wait until the VSC/traction light goes off.
7, Start the engine.
8, See the odometer.