Gs350inatx

I have an 07 GS 350 with 170k miles and it runs great until my alternator went out and caused engine fluctuations. I originally thought it was a battery issue and drove it to my garage where I purchased the battery. The engine was skipping here and there in order for me to get there. I had the alternator replaced and now the garage is telling me that my transmission needs new pump and some other things related to a new transmission. I'm no expert but it seems very unlikely that both the alternator and transmission goes out at the same time. Does anyone have any thoughts? Thank you for all input!

Sodium

Welcome to CL!

Tansmission problems typically develop on relatively long time scales, so you've likely had the problem (if there indeed is one) for a while. I'm guessing that they pulled codes while they were doing the alternator, and a transmission-related code came up. On 3GS models, seems like tranny issues are down to old fluid (Lexus considers ATF World Standard to be lifetime fluid, so many people don't change it, or wait too long to do so). Also, I recall seeing a thread where a couple people had bad ECUs, which caused unusual transmission behavior.

Anyways, a few questions:

1. Has the tranny fluid every been flushed or drained/filled?

2. Do you regularly feel any symptoms of a failing tranny (eg. gears slipping, rough gear changes)?

3. What data did your mechanic present to support his claim that the tranny needs to be worked on? And what exactly is the nature of the work he claims is needed?

ibidu1

iTrader: (1)

Worst case the transmission ecu went bad with the fluctuation of power.

I would take it to the dealer and have them scan it and see.

Gs350inatx

Thank you for the responses!

Sodium - No, I have never changed the transmission fluids. There seems to be some who do recommend that gets done, and others say never to do it. The change of fluids will cause for issues with the transmission.

As far as symptoms, I did not feel much going on. The only thing was that it downshifted a little hard (periodically) when I was traveling on the highways and had to brake, but that was it. So it could of been the start...

Mechanic said that there was zero pressure in the transmission lines, and that they need to replace.

ibidu1 - I spoke with the lexus dealership and they want me to take it in for a diagnostic check...

The only code that appeared was "VSC" when the alternator first went out, but that was the only one.

Sodium

Yeah I've seen arguments both ways about tranny fluid replacement. I wasn't convinced by the "it's a sealed tranny" crowd, so I recently did a drain and fill (12 qts over four drain/fills) – the difference is subtle, but I definitely notice an improvement. Now the argument for not doing a flush does make sense to me, especially with higher mileage and old trans fluid.

If you're referring to the downshifting under heavy braking, that's totally normal.

As for the zero tranny fluid pressure I haven't heard of that particular mode of failure on a 3GS tranny before. Haha did he forget to turn the car on before testing the line pressure? Here's something I found on diagnosing a failed trans oil pump.

ibidu1

iTrader: (1)

I would have the dealer diagnose the problem and if the problem is big take it to an independant shop for repairs. But atleast you wont throw parts/money at the car in hopes of a solution. The dealer is not perfect neither, but atleast they have the better scan tools to diagnose issues like this. An hours worth of labour is not much