Transmission Problem - Please Help

[Lexus-IS]

My 2006 IS250 has 160k miles on the clock. About a year and half ago the dealer replaced a solenoid on my transmission and added new transmission fluid to replace the lost fluid. Since then the car has been shifting not as smoothly, I read in many places that it must have been not put with the correct amount of fluid. So took it back to the dealer and mentioned this and they agreed to look at it, they agreed it wasnt shift correctly but said it has the right amount of fluid, so they just upgraded the transmission software. A year on from that, it has just been getting more and more jerky and this morning it kept flicking between neutral and gear while driving and jerking like crazy.

There is no engine light or anything but the transmission is feeling really jerky. I was driving and it kept going to neatral and gear back and forth for a while and felt like i was hitting a car everytime and getting whiplash. I put it on snow mode, and it still did it for a while but then calmed down and was able to calmly drive to work. But the entire journey the N and the D light was on together. and while this issue was happening, it wasnt switching to S mode.

Any ideas what this can be? Can insufficient fluid cause this?

Any help would be greatly appreciated.

Thanks

[johnatg]

I think it's very unlikely to be a problem with fluid level - that can cause jerky shifting, but not like you describe. Sounds electrical to me - solenoids/relays or the transmission ecu.

[Lexus-IS]

it was jerking like crazy for a minute or so as it just couldnt make up it's mind between N and D. Then managed to drive it fine in snow mode all the way to work which was about another 45minutes drive away. So called the dealers and they agreed to have a look at it later in the day. So I left work to get to the dealer which is about an hours drive. Was expecting similar issues to arise or some kind of issue, but no it's as if there was no problem at all and car drove without doing this all the way to the dealer. Strange thing is that if a car was to be in gear and then a person puts it in N and the back in gear back and forth, it shouldnt jerk should it?

The technician at the dealer test drove it and couldnt replicate the issue, he drove it hard and at first he thought maybe but couldnt find any signs of slipping. While i waited they put it on the ramp and inspected and plugged in the diagnostics tools and could not find anything wrong. But I just couldnt accept that as an answer because something is definitely wrong. A jerky shift i can live with but what happened this morning scared the crap out of me. Driving on the dual carriageway and the car is jerking and making gear switches.

They've agreed to keep it overnight and do a cold test drive. But I fear they wont find any symptoms.

What is the symptoms of slipping?

[johnatg]

Slipping symptoms - High stall speed. That's when a test is carried out by connecting intelligent tester, pressing hard on brake pedal and accelerating until the engine stalls. It should be ~2550 rpm. Do NOT try this at home!

Re moving from N to D or N to R there should be a shock felt - the time lag should be less than 1.2 secs and 1.5 secs respectively. If it's longer, it indicates one or more of the clutches is worn (I think there are 3 or 4 clutches)

I still think it sounds electrical - intermittent - dampness in a solenoid, drying out when it gets warm?

[steve2006]

I take it that your dealer is Lexus and therefore the correct ATF was used?

Also sounds like sticking shift solenoids to me,they can get gummed up and jam.

Why was the one solenoid originally replaced? They are normally replaced as a complete set on the Aisin transmissions.

[Lexus-IS]

@Steve yes the dealer is Lexus and I assume they used the correct ATF.

@John yes it does seem like electrical.

Any suggestions on what to do if this happens again or if anyone else is unfortunate to have this issue?

Problem is that if the dealer cannot replicate the issue and doesnt have engine fault codes then they dont seem to be able to do anything. Any suggestions what I can do? (Other than replacing the car, which will be sad because other than the gearbox issue, everything else is good)

[steve2006]

I'm surprised dealer level diagnostics cannot trace the fault unless it is a mechanical problem like clutches and brake bands in the transmission, my LS400 even has transmission diagnostics at over 20 years old.

It may be worth consulting with a specialist transmission specialist if Lexus cannot come up with a solution.

[Lexus-IS]

I am worried they wont be able to find anything and it's because of this reason why I just lived with the not smooth shifts as I thought they wont find anything. But with what happened this morning, it's something I cannot leave alone

[Lexus-IS]

@Steve, one solenoid was originally replaced because of a check engine light that came on. From time to time randomly while driving the shift would be slow to respond specially once warmed up so they tested all the solenoids and found one to be outside of the parameters which they then replaced. But since then it just hasnt been the same. They test drive it and think its normal but they drive it hard to be honest and when driving it hard i guess its not that bad but when driving it calmly the gear changes are not as smooth as they used to be. I'm wondering if it's worth spending money again at the gearbox because the solenoid job last time cost a fortune, i've come across a few breaker yards selling a complete transmission. One from a 2011 with 17k but price is quite steep at £1.5k and another from a 2007 at 48k at a better price of £550.

Also wondering if it may help to ask Lexus to do a complete gearbox flush, maybe that might help? but these units are said to be sealed with lifetime fluid so not sure how thats going to work out.

[johnatg]

They are not sealed - there is a drain plug and you can change the fluid. But they hold 7.2 litres and you can only drain 1.0 (or 1.5) litres (info varies) at a time, so it would take a lot of drain/refills to change the majority of the fluid. Probably worth one or two drains at your mileage, but I'm sure it's not the basic problem.

[ChrisIS200SportTTE]

They're not sealed for the lifetime of the car. Lexus just recommend that you don't change the ATF ever under normal driving conditions.

99.99% sure that your problem had nothing to do with fluid or fluid level (therefore making a flush completely pointless)

Your problem, as stated a few posts up has to be electrical or ecu or mechanical in the gearbox.

If it was me, I'd buy that transmission for £550 and fit it. Prob fix all your probs.

[noby76]

before you start throwing money at it best to take it back to the dealers for further investigation or alternately take it to an automatic transmission specialist near you for diagnosis.

[Lexus-IS]

before you start throwing money at it best to take it back to the dealers for further investigation or alternately take it to an automatic transmission specialist near you for diagnosis.

I have taken it back to the dealers and they couldnt replicate the issue and kept it overnight for a cold test drive and still cannot replicate the issue. They've called saying they cannot replicate the issue and that they've checked fluid levels and everything checks out fine. They've run diagnostics and there is no codes. So seems like i've hit a brick wall, what can I do now? They say they've done the checks and its got clean bit of health. But i know it hasnt and something is definately wrong. A bit like when doctors cant find anything but patient is adamant there is something wrong.

[johnatg]

All you can do is to carry on driving it but watch out for cold damp mornings (or some other triggering situation)! Maybe it was a one-off ocurrence - but it could easily reappear!

[Lexus-IS]

Dealer has had the car for the whole day and havent been able to find anything. they've run the diagnostics and cannot find anything at all. So the only thing they are saying now is that they suggest to keep driving it and if it comes back, they're hoping a code will register at some point that will help them diagnose the issue.

back when my solenoid issue came up which required the solenoid change, for many months i was getting intermittent lags. Basically car used to drive normally and all of a sudden and not always, once warm i would get a huge lag almost like a DBW delay. This was fixed by turning car off and on, then after good few months an error code finally came up indicating the shift solenoid issue. Wondering if it may be something similar and maybe another shift solenoid getting stuck. But will a stuck or sticky shift solenoid cause the N and D switching automatically? The car was going from D to N but jerking like crazy but if it was truly on N then it shouldnt jerk should it?

[johnatg]

It's gonna jerk if it's switched from D to N in motion!

[Lexus-IS]

Got the car back from the dealer, they said they've done all they can and only thing they can suggest is to wait for it to generate a code that can help them diagnose it. Drove it home and it was ok. I noticed something and not sure if it's normal as I cant remember trying it before. Can anyone check this on their auto for me please? If going at steady speed lets say on 5th gear and the rev is at about 1300, if i gently tap the throttle pedal the rev jumps by about 500rpm. Is this normal? should the rev not go up gently?

[johnatg]

It's normal - you've changed down a gear!

[Lexus-IS]

It's normal - you've changed down a gear!

No but at this point it's still in the same gear. One place where i notice the rev going crazy is when slowing down lets say for a junction and the gear drops to 1, but if i then want to move off and even gently tap on the throttle pedal, the rev goes over 1600 and back down

[johnatg]

That's due to the torque converter - acts a bit like a slipping clutch on a manual gearbox. Really - nothing to worry about!

[ColinBarber]

If going at steady speed lets say on 5th gear and the rev is at about 1300, if i gently tap the throttle pedal the rev jumps by about 500rpm. Is this normal? should the rev not go up gently?

That is normal until you get to a certain speed when the transmission should go into lock-up which stops a lot of slip within the torque converter. You should see that happening at motorway speeds for example.

[Lexus-IS]

I tested the time lag between N and D, its around 1 second or less and i can feel a little jerk when going into gear.

One thing i've noticed is that when driving at lets say 50mph and sometimes adjusting revs, i get that shifting feeling as if the gear has changed but it's still on the same gear. It also takes a while to go from 1st to 2nd. And when slowing down the transmission almost very rarely shifts down to 3, it goes from 4 straight to 2 then 1. Only on very few occasions i've seen it on 3.

[ChumpusRex]

I tested the time lag between N and D, its around 1 second or less and i can feel a little jerk when going into gear.

One thing i've noticed is that when driving at lets say 50mph and sometimes adjusting revs, i get that shifting feeling as if the gear has changed but it's still on the same gear. It also takes a while to go from 1st to 2nd. And when slowing down the transmission almost very rarely shifts down to 3, it goes from 4 straight to 2 then 1. Only on very few occasions i've seen it on 3.

All this is normal.

There is meant to be a 1 second lag when selecting D, and there is meant to be a soft jerk.

At above 40 mph, the transmission will go into "torque converter lock up" mode. When you accelerate the TC will unlock, and the revs will go up, feeling like it has changed down gear, when it hasn't. When speed stabilises, then the TC will lock again, and the revs will drop, feeling like it has changed up gear.

The transmission is also designed to miss gears out when changing down, if necessary - and it will change from 4 straight to 2, if you push the accelerator hard, or the mode selector is in power mode. It will also shift up several gears, if you have been accelerating hard and then let off.

[Lexus-IS]

OK guys, so i picked up the car on saturday was fine but to me the gear changes just felt way to jerky compared to usual. Anyway, so as the dealership advised. Drove it to work, all ok. On the way back home however, i am about 10 minutes away from home and as i'm coming to a stop i get a very sharp jerk almost like i did an emergency brake, thats exactly the symptom i had last time. So looking at the dash and bingo the neutral starts to flicker. So basically D and N is now on, so put it in snow mode to drive into side road and stop.

So, I stopped the car and when i put it on R it's fine but as soon as I put it back on D, i get a huge jerk (not the usual soft jerk, almost like i'm being rear-ended) and N and D are lit together. So tried putting on P and then trying again, but still same thing. So tried turning car off and on and this time i got the check engine light and VSC off message. So put it on snow mode and slowly drove home which was about 5mins away. Snow mode seems to work even though both N and D get lit together.

So i got home and plugged in my OBD scanner and read the code and it reads: P0705 - Transmission Range Sensor "A" Circuit (PRNDL Input)

Going to call the dealers first thing in the morning.

Any idea what this is? Could it have something to do with some kind of switch or the fact that last time they update the software on my ECM?

Will a faulty switch cause non-smooth gear changes?

I read the lexus tech doc on this code, and it states the following:

• Test the PARK/NEUTRAL POSITION SWITCH ASSEMBLY - if not good then replace
• If OK then test the TRANSMISSION CONTROL SWITCH - If not good then replace
• If OK check HARNESS AND CONNECTOR (PARK/NEUTRAL POSITION SWITCH - ECM) - If not good REPAIR OR REPLACE HARNESS OR CONNECTOR
• If OK REPLACE ECM
  

[Lexus-IS]

This morning I started it up to take it to the dealership and the N and D were not getting crossed like yesterday. So seems like letting it rest solves the issue. Must be some kind of electrical fault which seems to randomly occur after a while of driving. Anyway the code is stored and have dropped the car to the dealer. Lets see what they say