Sherl

My (98 LS400 with 262k miles) transmission has been acting lately. I did fluid drain and refill through cooler lines as well of over 8qt, and the probelm disappeared for less than a week and now it persistently reappeared.
Whenever I start the car for the first time, I need to rev the engine over 3200 RPM couple of times and I can see then the car shifting from P to D, also the car at times CAN roll back in this process even when in D. Once the shifting happens for the first time and until i turn off the engine everything is fine. No gear slips, shifts as normal and everything appears to be as normal.

If I let it sit for say three hours and again the same cycle repeats, sometimes even less than an hour if I let it to sit, I need to go through this cycle of revving the engine to let the car shift from P to D. I have P500, P325/P330 on my CEL. I am aware about the codes but any of these codes cause this behavior? Atleast I am aware that the 325 happened previously I wasnt having this issue. The car isnt in limp mode which was the case when 325 happened previously (no 330 back then).

Any idea where to start? a local indy shop says that transmission is going out and looking at 1500 for the labor alone. At 262k miles and this transmission had regular 2qt drain and refill almost every 30-40k miles. Is there any vaccum leak, solenoid issue or any sensor or TCU/ECU going bad can cause this issue?

paulo57509

It appears that there are two separate issues. I can't see them being all related to one issue. The only thing that may be causing the behavior you describe (or contributing to it) is the P0500 DTC. This is a speed sensor malfunction.

There are two of these on the transmission. One is for road speed, the other reads the torque converter speed (I think this is why it's there). They're the same part number (one is for the sensor itself; the other is for the sensor and o-ring = 89411-50010).




I would try swapping the sensors; put the front one in the rear and vice-versa. Hopefully your speedometer works - swapping a faulty sensor for a faulty sensor isn't going to tell you much.

Sherl

I did test the speed sensor thats on the torque converter (need to wiggle near the transmission mount to get it out) following the factory manual with magnet and multimeter. It appears to be working but can still fail (?).

Yamae

I'd start checking the AT's internal line pressure using the method below link or an equivalent method. The slow gear engagement is often caused by the lower pressure which relates to the clogged strainer, clogged pressure line or the insufficient ATF level.
https://www.clublexus.com/forums/ls-...ml#post9898006

Sherl

It's pretty instant when it engages. Not like the vehicle will slowly move in D. An harsh engagement to D from P when I rev iI. Also if it's low line pressure, it should happen every time right? It happens ONLY when it sits for extended periods of time. And the link does mention ECU rebuild fixing the issue, does 98 can have the same fatality (?). The car live 20 years in Southern California and back when I opened the ECU in 2019 everything looked alright so I just put it back.

I was wondering warm capacitor vs cold capacitor has something to do(?).

Yamae

Yes, warm capacitors work better than cold ones.

Electrolytic capacitors dislike cold temperature. Nichicon's P series capacitors were designed to work well at lower temperature compared with other conventional ones. Those also show lower ESR even at lower temperature. That was the reason why automobile industries used them in the late 80s up to the end of last Century. Later on QAS capacitors were found to be weak. They die prematurely causing the corrosion and the QAS liquid leaks out. They didn't follow the Arrhenius equation.

98-00 LS400s/Celsiors also use Nichicon's QAS capacitors of P series but the lifespan of those capacitors is usually a bit longer than earlier models due to the smaller ripple current and the lesser stress. But those are still QAS capacitors and they fail sooner or later. 98-00 owners should also replace those capacitors before problems start. One of typical symptoms of 98-00 is the strange or rough shifting of the gear, as I have been mentioning. This is another one.

Sherl

So do you think with the above symptoms would it has to do with pressure line or ECU? I was thinking warming the ECU with hair dryer to see if it makes a difference

Yamae

It's a good idea to use a hair dryer but I'd check the ripple level using an oscilloscope for the precise judgement. Anyway 25 years old simply means that it's time to fail for those capacitors.

Losiracer2

I had an issue with my 97 w/ 290k, where there was a noisy fluid pump and very lazy shifts. Didn't get as bad to the point of yours though, but shifts would take awhile. I had to replaced the transmission strainer behind the pan. This immediately took care of the noise and you can tell it was completely clogged with particles. FF about a year after I sold the car, the transmission needed a rebuild. I did sell it to a guy with a 16 yr old son though, so that may have sped things up regarding replacement as I didn't drive it too hard.

But a new strainer at Orielly's for $18 is what took care of it comes with a gasket, or dealer which is about $60 but then you'll need the 1281 FIPG (about $23 a tube) to seal the pan, what I'm currently using on my 99' when i resealed the pan.

Sherl

It so happens for me only the first time or when it sits for extended periods of time in a day. If this is a clogged strainer wouldn't that be each time? The strainer was replaced at 180k IIRC.
There is no hesitation once it shifts. Only the P to D going crazy when it sits for a while

Sherl

I'm going to drop the pan and see if it works. But when I did 8qt flush using return line, it worked great for two or three days. So I'm thinking to install a Magnefine 3/8 inline transmission filter too. Anybody have any comments or recommendations?
should I just cut the return line with a saw and just install it or any other tips?

https://www.napaonline.com/en/p/ATP18721