I have a 1999 Lexus ls400 with 175,00 miles. I bought it for dirt cheap from someone I know . When I got it it had a code P0763 “For Shift Solenoid C” which I know mean the tranny is probably dieing out but I thought there could be a chance that I could save it and worst casenario I would have to rebuild or replace the tranny which I have no problem doing.

The problems I’m having with the car is when I press on the gas sometimes the transmission slips usually from 1st to 2nd gear and sometimes 2nd to 3rd. I replaced the shift solenoid, the filter, and put brand new Toyota ATF transmission fluid in hopes it would stop slipping. After replacing all that and driving it, afterwards it felt a little better with less frequent slipping but after 2 weeks it’s basically went back to slipping more frequently. Well a week ago my car stalled on me in the street the first drive I took it after flushing the coolant (previous owner had green coolant) and replacing the thermostat and the coolant temperature (because my coolant temperature gauge wasent accurate) after 5 mins of taking my car on a test drive around my neighborhood my cars rpm went down to 0 and a check engine light came on and it stopped moving. After like 5 minutes of just letting it sit I turned it back on and the check engine light went away and it drove like normal afterwards except now my rpm and my speedometer aren’t accurate. Also the temperature gauge still doesn’t work. I tried to look for the check engine code with my scanner and nothing popped up. I thought maybe the ECU could be the problem. So I went to get the ECU tested and checked out and they said it was perfect and had no problems.

So could it possibly be just my transmission need to be replaced or rebuilt (which is better) and what about my temperature gauge?

 

It sounds like you're having multiple issues, as I can't see the transmission affecting the way the engine runs.

• Transmission slipping.
• Incorrect coolant.
• Intermittent (happened once) engine stops running.
• Gauge inaccuracies.

Transmission -

1. Do you know why the car sold for dirt cheap? Perhaps the transmission was abused (treating it like a manual when it's an automatic) and it now has internal, mechanical damage (not just electrical)?
2. Did you refill with the correct ATF? Should be Toyota T-IV (or any ATF equivalent to Mobil 3309).
3. What did the drained ATF look/smell like?

Coolant -

1. Did you drain the engine block of "green" coolant as well as the radiator? Green and Toyota LL don't mix as they're different chemistries. Did you also flush the system with clean water?
2. What kind of coolant did you refill the system with?
3. Did you properly bleed all the air from the system?
4. Did you install the thermostat with the "jiggle pin" in the 12 o'clock position?
5. Did you disconnect any sensors/senders? You might want to go back and check them for full connection or bent pins.

Engine - This one is hard to diagnose through a forum post.

1. How is the health of your battery?
2. How is the health of the charging system?
3. Who tested the ECU?

Gauges -

1. Will your scan tool read data stream? You can compare what the ECU is seeing against what the gauges are telling you. This will narrow down whether it's an input issue or a gauge issue.

 

Previous thread about this issue with a lot of questions answered already:

https://www.clublexus.com/forums/ls-...t-working.html

 

Transmission -

2. Yes I refilled the transmission fluid with the correct Toyota Type IV Transmission Fluid.

3. The fluid was pretty much black or very dark red. I didn’t get to smell it tho.

Coolant -

1. Yes I drained all the green coolant from both drains from each side of the engine block and the radiator. I did also drain the radiator and flushed the radiator with water.

2. I refilled it With Peak Red/Pink Asian Vehicle 50/50

3. Yes I followed the instructions from the coolant housing. The car doesn’t overheat at all.

4. Yes when I installed the thermostat the jiggle pin was all the way at the top.

5. I only replaced the coolant temperature sensor didn’t touch anything else.

Guages -

With the scanner tool you can compare this screenshot that I took to real time gauge reading. They aren’t accurate at all with the scanner tool





The speedometer guage is also about 5mph in accurate fore example the scanner says I’m going 35 but the gauge reads 40.

Engine -

1. Haven’t Checked

2. Haven’t Checked

3. I sent it to this shop that does repairs on ECUs from different cars and they said it was fine. I opened up the ECU to look and see if any capacitors weren’t melted and they all looked fine but I know it doesn’t have to be melted for it not to work so that’s why I took it to a shop.

 

The transmissions was probably worn from use and neglect with fluid changes, so changing the fluid probably hurt you more than it helped:

Likely any friction material floating around got flushed out by the change.

When buying a Toyota, you really want ones that have had regular transmission fluid services. If not, changing it very late can be a nightmare it seems, because the damage has been done..