my '96 LS400 will be running fine, then suddenly the following things will happen simultaneously, but with no codes set in ECM:

green PWR transmission mode dash light goes off
check engine light comes on
transmission no longer will shift automatically, must be manually shifted in order to drive
A/C stops working
Front defog red light flashes approx. ~10 times
speedometer not working, remains at 0
engine runs poorly
bad smell from exhaust

then seconds or minutes later, the check engine light goes off, PWR light comes on, and everything above is now working perfectly!

I am thinking that very few things could cause all of this at once, my candidates I have thought up are: ECM, TPS, crankshaft position sensor, or perhaps main engine relay or EFI relay --- any other components that might be the culprit?

and there is no pattern to it, no time pattern, no engine or ambient temp pattern, as random as a loose connection and NO codes set in ECM

anyone recognize these symptoms?

 

Guys, seriously

I need help! - someone has seen this before.

what does the flashing front defog light mean, is it a code?

how many things on the car could make the transmission not shift, A/C not work, and speedometer not work, then suddenly go back to everything working fine with no codes set?

 

Bad ground?

 

Trunck harness possibly.

 

+1 Check the harness at your trunk near the hinges for breakage or shorting. If that is not the case then I would look at the ECU itself. Some of your symptoms are similar to when the ECU is reset, such as the defrost flashing and no A/C till it goes through its self-check mode.

 

this is what i was thinking too, some kind of disruption in battery connectivity/power supply. The defrost light will flash when the climate control system is powering up for the first time, like after you've had the climate control unit unplugged. Thats also why your A/C would stop, as the CCU is setting itself. Check the big ground strap that bolts on near the ac compressor. Mine was WAY loose when i got my car. The bolt was almost backed all the way out..

Also, I may be wrong, but I thought the trunk harness problem was only in gen1 LS?

 

the thing is, it is more than a reset, it can stay in this screwed up mode for days or just seconds, even blink back and forth from perfect to screwed up, no pattern!

I will check the grounds mentioned

where are other grounds located that have also been at issue on LS400's?

 

It seems to me that the ECU enters the safe mode. When the DC for the main processors is not stable, the ECU enters the safe mode. Have you ever checked cold solder joints or cracked solder points for the DC regulator circuit in the ECU unit?

Tapping the ECU can sometimes duplicate the problem easily. I suggest you to monitor the voltage for the Vcc line which is the output of the DC regulator while tapping.

 

Wow - great info!!

this is what Club Lexus is all about!!!

 

Whats the code?

 

Trunk harness is typically with the 1-LS. There have been posts about ECU issues on 95 and 96. I would initially suspect a grounding issue. Check the battery cables and trace back through the harness for any signs of damage, etc. Like critters making a meal of the wiring looms.

 

could someone direct me to the location of the most critical ground straps on the car, for this kind of issue?

the only one that has been mentioned here is the one near the A/C compressor

I have the factory service manual, but it is rather quiet about the location of the most critical ground points