TDIGREEN1

Alternator output fine. Fans off but now don't run w/AC on. AC pressure switch good. ECT switch good. Main fan relay good. One cooling fan relay seems intermittent when testing and getting a little warm - replacing that next.

Next have to begin looking for oil leak coming from vicinity above and behind the timing belt tensioner - or behind the PS pump - not PS reservoir o-ring - does not appear to be PS fluid - PS operation normal. Only a drop of oil on underside of shield on bottom rear of alternator. PS fluid level normal and fluid does not taste or smell like ATF - not quite enough of it to be absolutely positive. Noticed a little dampness on rack & pinion boots and wondered if something could cause an overpressure in the PS system. Maybe i'll clean the PS solenoid screen for kicks.

Valve cover gaskets I can do. But don't have any oil on the headers. Man, a small amount of oil goes everywhere....and there are lots of opportunities for an oil leak in that area. Might be time to find a decent LS400 tech.

LScowboyLS

Alternator output may be intermittent, that is what happens right before power steering fluid takes out both your alternator and battery

this is super common on LS400, due to the fact that power steering leaks are so common on LS400, and many times it is just the $3 o-ring between reservoir and pump!

LScowboyLS

good LS400 techs are exceedingly rare, and you are already in the place where the last of them hang out!

I would recommend that you become the decent LS400 tech! - we will guide ya!

believe me, nothing more frustrating than getting clipped for many hundreds of dollars from someone who knows less than you do at this point, and sadly, this is the rule rather than the exception!

invest that money into good factory service manuals, wiring diagrams, and tools!

TDIGREEN1

You are right about finding decent technicians. Found a good tranny tech and asked if he would replace the rear crank main when it started leaking. He was happy to do it for $500 - but he set the seal right back in the old groove even after I explained it and asked him specifically not to seat it all the way in. Of course it still leaks a little oil from the bottom of the bell housing - made a little oil catch well and tampon holder bolted to the bell housing. Never leaks a drop on the floor and none on the exhaust except on a long drive.

I'll tackle this thing again when my part arrives - maybe knock out the service on the PS pump& solenoid screen and see if I can find that oil leak.

TDIGREEN1

FWIW the oil leak was from the cam bearing cap. When replacing the cam cover gasket go ahead and pull the caps on both sides, clean and apply a 'thin' coat of FIPG sealer then reassemble. Leak gone.

As for the electric cooling fan control circuits I gave up trying to identify the problem as all normal fixes failed to work. I did learn that the left side fan relay - the one controlled by the AC pressure switch - can be jumped out to run the fans on low all the time. The terminals to jumper are on the bottom - the two that are parallel to each other - that's the switch. The top two that are in-line with each other is the coil - just leave those alone.

The only issue after that is the other cooling fan relay - the one controlled by the coolant temperature sensor - is getting hot. Not sure if that is the coil in the relay - since these coils are energized at all times when the ignition key is one - but I will replace it and see. I think that one is original.

ImEbo

I know that i’m a bit late but

i’m doing a project on a ls400 96 US model apparently if i removed the ect switch (the temp sensor) fan will run on full speed but what ever i do and what ever the temp was the fan will not go more then low speed what so ever even if the ac is ON on full speed lowest temp

have you figure out what is the fan problem

btw the fan will not start with ac unless i turned on AUTO mode