ucfkid17

I have a 1995 Lexus LS400 and i took it to jump my friend’s car once. I wasn’t exactly paying attention but my homie reversed the polarity on accident. Ever since then, i’ve had a battery light. Naturally, i replaced both my battery and alternator but the light still comes on. I scanned the CEL and found the P1600 code. I’ve heard that if my car has that code then there is an open circuit or something and that my ecu may be kaput… but my car hasn’t shown ANY symptoms of a failing ecu and doesn’t lose power whenever that battery light pops on. Idk my next move… should i buy a new ECU, or what? Thanks in advance guys! i’m new here 😭

Butterjamtoast

Hi, have you tried disconnecting your battery for a few minutes?

ucfkid17

Yeah, but i unplugged just the Negative terminal. Should I unplug both terminals?

paulo57509

Speaking in general terms as I don't have a '96 wiring diagram....

TDC P1600 shows up when the ECU is no longer getting voltage with the ignition switch OFF. The ECM needs constant voltage at all times in order to maintain the various memories that are stored.

The easiest thing to check would be the EFI No.1 fuse to see if it's open. If the fuse shows continuity (is OK) then the issue is someplace else and more involved diag is required.

ucfkid17

Yeah, that makes sense. I checked my EFI No.1 fuse and it was fine. Where else should i look or check for any inconsistencies?

paulo57509

See attached. However, this is the diagnostic page out of the 1998 model year. Go back and start at step 1. The pin out for a '96 is probably different than what's in the attachment (it's for a '98 model year). Hopefully, someone has access to a '96 diagnostics for this DTC.

Keep in mind that the appearance of the P1600 was caused by reversing the battery connections and not due to "normal" circumstances. The diagnostics for P12600 may not apply because the reverse polarity issue is not considered in the attached pages.

After reading other posts where someone has connected a jumper battery in reverse, a lot of crazy stuff will occur. I don't think the correction is straight forward as it might first appear. Just a sampling...

https://www.clublexus.com/forums/ls-...backwards.html
https://www.clublexus.com/forums/ls-...backwards.html
https://www.clublexus.com/forums/ls-...rds-ucf20.html

ucfkid17

Thank you Paulo, i’ll refer to those and see what i can find!