Started Car Sunday morning and pulled out of house. within 400 ft dashboard gets all CEL (VSC,ABS,etc) power steering and ABS are out. Turn car around without power steering and drive back to driveway. as im driving the dash lights go off. hook up OBD scanner and get nothing except C1241 (Current low or high power supply voltage) and PO504 (Current Brake Switch A/B Correlation). Brake switch was replaced two years ago for same issue but none of these issues were present. Shutoff Lexus, Took wifes car and left.

When i get home battery is dead (its a one month old Optima red top). let it sit on reconditioner overnight (up to 12.6V now). as soon as i hook the negative terminal up the dash lights come on as if its in IGN/ON setting. Car does not recognize key fob, have to use manual key to open door. Car does not recognize key to start OR shut off car. Only way i can power down is to disconnect the battery again. Car makes no sound when i try to start since its not recognizing key, IGN switch changes color when i press brake switch.

Very lost here. on one hand i feel its def a bad alternator, but cant really check anything as im having the issue with the key. anyone had same issues? possible immobilizer activated and how would i reset. spent hours last night trying to diagnose further and reading online. nothing seems to match my scenario.

 

Your initial symptoms sound like a bad alternator. Your secondary symptoms sound similar to others who have had an "oops moment" reconnecting the battery, e.g., briefly connecting it with the wrong polarity (or briefly connecting jumper cables with wrong polarity), possibly blowing the fusible link or worse. Not saying that is the case here, but since others are not always forthcoming about what they did, I thought I'd mention it.

 

JM2C but when these highly evolved electrical systems loose voltage rapidly, bad packets of data are sent all directions and rare events like this happen.

Best guess is you get an alternator in there, and search this site for repairring sequence to handshake the fob and Immobilizer into talking again. This is not the first time this has happened so you are not alone.

 

how many miles? my 250s alternator gave up the ghost at 220k and i've heard others have died earlier than that. my symptoms were the same; dead battery when still good, no start or key recognized.

 

I had the same problem with mine, battery going dead every so often (overnight or just sitting with music playing). Thought it was battery so got that replaced but issue persisted. Turns out it was the alternator, got that replaced and haven’t had any issues since. I know this isn’t too helpful but maybe have the alternator looked at and go from there?

 

My alternator on my 2006 IS250 went out at 94000 miles. No warning and similar problems.

Would advise that you use only a Denso replacement as there are multiple reports of non OE replacements causing further issues.

 

Same thing happened to my 2007 IS250 at 95K. It turned out to be the alternator. Pain in the neck to replace because of the hidden bracket that is hard to reach. Some write-ups here shows how to do it. One write-up shows with a controller cover removed from an on-board computer to get access. YOU DO NOT HAVE TO REMOVE THE CONTROLLER COVER. Simply remove the bolts holding the controller case so it can be moved to gain access to the aforementioned bracket, if you decide to replace it yourself. NAPA sells an OEM DENSO alternator that is an exact fit. Dealer will probably charge you 2x the price for it.