Stroock639

1999 LS 400, 100300 miles, every so often will not change out of 4th gear, unless you either set the cruise control or give it a quick bit of throttle. when you do set the cruise, the rpms will rise by 200-300 and then shift. this happens more so when going down a hill (car has factory HIDs so it knows when its facing down i guess). my mechanic has an LS 430, and claims that his has done this since it was new, and other people have also commented on the same issue. i'm not so sure since i only remember this start happening a year or so ago. transmission fluid was recently changed, and the occurrence persists.

fixmiester

Possible you have a vacuum leak? Low manifold vac keeps the trans from upshifting;releasing the throttle after achieving a steady speed would also allow an upshift, even with a small leak.That's what is happening with the cruise control. Does your pedal seem to stick sometimes, causing light acceleration? That will also delay a shift to OD.

Stroock639

i don't think it sticks, and i should have been more clear, when it won't shift (only occasionally) when i lift off there is an engine braking feel, until i set the cruise control. i've never experienced any sort of unintended acceleration.

Stroock639

can someone else maybe please shed some light on this?

Gene01

This may not be of much help, but...
You could try to start a thread (or add to a current one) in the LS400 forum.
Two members who frequent that forum are LScowboyLS and Yamae. They have extensive background in Aisin transmissions and electronic systems. Let them know that it is LS430, not LS400, but I imagine that they may be able to give you some worthwhile direction.

JBrady

One of the indicators for bad capacitors in the ECU is transmission shift issues.

Review the thread "All my crazy issues solved.." and strongly consider looking into this.

Purchase only the quality capacitors from the sources listed and have them replaced by a skilled solderer who is well practiced with printed circuit boards. Even if this is not your issue it IS an important ISSUE.

https://www.clublexus.com/forums/ls4...capacitor.html

RA40

iTrader: (6)

The 98 is a remote possibility but among years following, this would be the first instance I recollect reading about. Not that there cannot be an ECU related issue, it seems odd. Any codes being thrown?

What was the condition of the fluid prior to the change? Has it been regularly maintained? If not, it will take several incremental drains-fills to flush the fluid. If the fluid was black-burned, a one shot flush service is The other is that the shift solenoids may need to be replaced and tranny screen cleaned as well if the fluid additive package was depleted thus the fluid will be black-burned.

Stroock639

when the fluid was last drained it was apparently very dark, his exact word was "black." damn lexus dealership claimed and charged me for changing the transmission fluid and I guess they didn't, one of the many reasons I'll never go there again. if anything I'm guessing that's the problem but I'll also try and find a vacuum leak. is there a difference between the ECM and ECU? 8966250010 is listed as HARDWARE, ENGINE CON and is $7,558.64 and 896615050284 is COMPUTER, ENGINE CONTROL and is ONLY $1,301.67. when you're talking about leaky capacitors, which one of these are you talking about? if it's the cheaper one I'd rather just buy a new one

RA40

iTrader: (6)

Very doubtful this is an ECU with leaking capacitors. Yamae has mentioned Toyota updated the capacitors for the '98 and by '99, this is very unlikely the cause.

The black tranny fluid is the first issue to correct. Generally, at 60K intervals it will need to be incrementally drained. On short stop-go drives, the fluid tends to get darker quicker though that does not mean the additive package is depleted. If the fluid has gone 100K miles, it is highly likely the additive package is dropping significantly.

This fluid drain is an easy DIY and the cost is roughly $12. You'll need 2 bottles of Type IV tranny fluid and the crush washer. Buy a third bottle because what comes out is not always exact and is relative to how long you leave the drain plug out. Typical drain is just about 2 quarts. What comes out, put back in. Do this routine every oil change until the fluid is nice and red. On trannys with burnt fluid, a massive drain with fresh fluid unsettles any sticking deposits so having that flow through the system is not a desirable outcome. This gradual fluid replacement works very well.

The tranny should begin to shift better but also read the threads about cleaning the screen and shift solenoids.

Stroock639

it hasn't gone that long without being replaced, from what i understand doing the flush with a pump inlet machine is a good way of doing it as opposed to the way that puts extra pressure on the trans so maybe i'll go somewhere to get that done. i don't think there's any damage that would make flushing it a bad idea, i don't see any particles or anything on the dipstick. and there's no check engine light or anything

Yamae

I need to add some more. The '98 and by '99 still use those risky capacitors that contain the quaternaty ammonium salt. Those capacitors have very high possibility to leak when aged. Compared with before the '98 and after, the newer processors for those do not require bigger energy/current compared with former ones and the electrolytic capacitors are not stressed seriously and the delta T (temperature rise) is less. This probably makes the failure rate not that high compared with older models.

As I help shop owners who are my friends, I have encountered 2 ECU failures for the '98 Celsior. One showed the delayed AT shift. The other showed rough engine running when at full loads of alternator such as head lights, fog lights, A/C with full speed of the blower, defroster and stereo with big sound are ON. There were some posts at the Forum that reported the delayed or strange AT shifts. Come to think of it, the AT control circuit in the ECU requires bigger current than other processors and capacitors used at the circuit are stressed more than others. Probably this may the reason why some of newer models have AT problems caused by the ECU.

I don't know that Stroock639's AT problem is related to the ECU or not, but I suggest him to check the ripple voltage at the DIAG connector.

RA40

iTrader: (6)

Thanks for the update Yamae. Will be interesting to potentially head this off if it is another capacitor issue in the ECU. (Getting ahead of myself, I don't want to think what may be ahead in terms of the LS430 and 460's down the road.)

sha4000

iTrader: (1)

Im glad that Lexus just gave me a remanufactured/updated ECU.

Stroock639

mine was manufactured in May of 1999 so i don't know if that matters Yamae. i want to rule out a vacuum leak first before worrying about the ECU. and can someone please explain the difference between the two part numbers i listed in post #8?