xtr3me

Looking for a diagnostic flow chart or electrical schematic drawing related to DTC B1261 Engine ECU Communication Stop
Cranks but no start
Key turned to ON position the following conditions are noted
1) no check engine light displayed on dash
2) cooling fan turns on and runs
3) headlights turn on with switch off

2A) cooling fan shuts off when relay removed
3A) headlight remain on with headlamp relay removed

alextv

First what is the year and model you have. Also did this just happen or a car acquired in this shape. Strange symptoms here as with the relay removed there should not be voltage going to headlight (not even feedback). Wonder if fuse box had water damage and shorted underneath.

xtr3me

A little history
Yr 02, been in family since 08. It’s haunted, I tell you. Just ask friends and family. wipers and sun roof operating on its own, which I attributed to a battery issue

The car has sat for several months, installed new battery. Performed oil change and took for a short road trip. Acquired the VSC off, check traction and ABS lights. Performed zero calibration procedure using paper clip, only this time I noticed the VSC off light remained solid and would not blink during procedure.

Memory reset and zero calibration performed using a Topdon Lite 2 and my friends Snap On scan tool . Same scenario, light remains solid during calibration - Test Mode. The codes can be cleared but return as soon as car moves..

Below freezing temperatures expected here in SE, pulled car in shop to drain and refill radiator with new antifreeze. The next morning the vehicle would not start. Scan tool does not recognize engine ecu but retrieves dtc b1261

After reading your post, I think you may possibly be correct, I forgot , until now... while diagnosing the B1336 Zero Calibration Undone code, I noticed the turn signals didn’t work. Several days later, started working again. I’m now wondering if it may have rained while the the sunroof was open on its own and water has run down the front pillar into the drivers junction box that the flasher is connected

alextv

I feel the VSC and other problems are not related. Do you have a voltmeter (very important now)? I know a new battery was installed but can be drained quickly by a trunk light staying on overnight. Does the car crank but not start? I would start with after checking battery to disconnect battery and pull down driver side fuse panel to inspect. Then hook battery back up and with voltmeter find out why headlights are staying on with relay pulled. Really sounds like a heavy short somewhere. Are you saying the wipers and sun roof problem originally was fixed by replacing the 12 volt battery? That's extremely strange. For the VSC problem you would think a quality tool like Snap On would work but I have seen where our LS430 is very picky on what doesn't trip that VSC problem when accessing the OBDII port. For me if I don't do it exactly the way techstream prompts and do the test at the end it will not work. Water damage can cause enormous problems.

alextv

Also don't know if this applies but a lot of people have mentioned there left taillight leaks water into the left wheel well in trunk where there is fuse block. Several have had to replace the panel it was so bad. Just looked and Ignition relay is there along with moonroof and lots of other fuses. I would check this first.

xtr3me

Thanks for reply, I appreciate you!
The battery tests good, tested with Midtronic battery load tester, it’s old, maybe 8-10 yrs but it’s been a reliable choice. I do have several multimetersMy mechanic friend whom owns the Snap On scan tool says he has never had an issue performing zero calibration on Lexus/Toyota until now.

The trunk junction fuse box is good. Headlight and fan turn off when fr Ig fuse is pulled from drivers side junction fuse box in engine bay. Also, when AM 1 fuse is pulled from junction fuse box , driver kick panel. I tore my MCL, so I’m moving pretty slow for now, wanted to hire my friend out but he lives 4 1/2 hrs away.
iv”e read where several Lexus GS owners have had fault ^ no engine light, no start and fan turns on with key on... unplug sensor on fuel rail and vehicle would start, sensor shorted

alextv

This has got me real curious. I will be back home in couple of weeks and have full manuals including electrical for my 2001. The headlight relay is there for a purpose for heavy current and the voltage goes to the headlight when the contacts close and only that supposedly. Don't understand how headlights can stay on with relay pulled. I will look at electrical diagram and see if that is even possible. Also make sure you have a good engine and battery ground to chassis as that can cause a lot of problems. There has to be some sort of feedback going on here. It will crank but just not start right?

Yamae

I don't know my experience is applicable to you or nor but I had similar problems at shops and dealers with Toyota/Lexus cars which sat for many months or more. The battery was drained but there remained some voltage. A newly installed battery was OK to work the starter motor but the engine doesn't start or the car has some strange problems.

These cars were fixed just doing a technique to discharge the remaining electrons in the ECU and other control units. The technique only needs a wire with alligator clips both ends. All I did were to remove the + battery terminal and connect the wire instead of a battery. The wire is used to erase/remove remaining electrons. It often needs to wait a day or 2 while doing this. The wire passes through stray electrons a little by little.

The electronics units have different kinds of devices inside and some devices hold electrons when the battery is drained very slowly. It is a common problem among PCs too. PCs that were sitting many months with a weak 2032 battery tend to have non working problem even after the battery is renewed. The remaining electrons in the CMOS memory causes the problem. To fix this, I always try short-circuiting the battery terminal for a day or 2 and install a new 2032 battery. Voila the PC works again.

xtr3me

If I recall correctly, they refer to the ecu capacitors holding voltage after a battery has depleted itself as logic lockup. For corrective communication issues, I was taught to remove key from ignition, disconnect battery and hold negative and positive battery cables together for several minutes to discharge capacitors

I thought of this but figured since I left the battery disconnected for several days to prevent draw from draining battery that the computers drained themselves
I’ve never fixed an issue performing this procedure but I’m ready to claim I have. Try this tomorrow... Thanks

LS430Nole

Did it work?

xtr3me

Follow up- fixed
So, aquired some schematic drawings and devoted the day to the LS430
Humid and hot day here in SE Ga, I pushed the LS on the side of my shop in shade, swapped ecu to program and sound of running fans annoyed me so I unplugged and this is when I noted ... wait, at this point I would like to both give a big shout out to all helpful contributirs of thread and also apologize for misleding info - fault / defeincy .
My helpers confused running lights with headlights, to their crefit, position of car in direct sunlight enhanced brighter appearance, not confirming - my fault
] swapped ecu but was unable to program to key using the obd paper clip, -connectors 4 /13, no flashing lights, plus no CEL on cluster.

CORRECTIVE ACTION
● replace faulty ING 2 relay - fixed - key on running lights illilumated, both high and low cooling fans running and no CEL
● replaced Vsc ecu with known good ecu - fixed abs and vsc off faults. After test drive vsc off light returned, scanner exhibit code for Zero Point Calibration undone. I was able perform calibration using my obd scanner