I have a 2005 3GS 300 which are known for having issues with solenoids and stuff. Car was giving a P0761 error and I took it to the local Toyota dealership for a check. They said the solenoid between 3rd and 4th gear is causing isssues, so I ordered a new OEM one and they replaced it. Car was shifting smoothly and the issue seemed to have been resolved up until yesterday when it got stuck on 3rd gear again. I read the error codes again and have the same P0761 code. I will be bringing it back to the dealership next week but am also looking for other suggestions. Thanks!

 

This code, like most all codes, tells you WHERE the PCM is detecting a fault, not what part is at fault. To properly diagnose it in this particular case, you next do a line pressure test on the transmission and compare that to the transmission solenoid shift diagram. Most shifts require more than one solenoid to be involved, and you can deduce the faulty solenoids from which shifts exhibit low line pressure. If line pressures checks out, then you can suspect a fault in the reference sensors, which the PCM uses to establish the baseline (“reference”) for its fault measurement. If the reference sensor is faulty, the fault detection will be incorrect.

In this case the reference sensor that usually fails is the output speed sensor. They are cheap, and if someone is unwilling to do a line pressure test, it’s best to throw this part at the problem first, when throwing parts at the problem is the preferred method vs. proper diagnosis. It’s cheap and can be changed externally without opening the transmission.

In your case, since you’ve already established *reasonably well* that the fault reading is not related to a shift solenoid, I would go ahead and change the OSS as it’s cheap ($20) and easy (20 minutes).

Before anyone opens a transmission to swap a solenoid, a line pressure test should be done to verify that. Otherwise it’s a guess, and a not particularly easy or cheap one.

 

Thanks, Oro!

I did take it to the local official Toyota dealership and asked them to diagnose the whole car but pay closer attention to the transmission. They came back saying that the only faulty part is this one solenoid but I have no idea how they came to that conclusion. No idea if they did a line pressure test.

I will bring the car back to the dealership this week and ask them to, hopefully, do a line pressure test and in the mean time get a new OEM OSS as it is in fact not expensive at all.

I'll reply back to this thread once I hear back from them and have the new sensor installed.

Thank you once again!

 

It is questionable if they would do a line pressure test - most Dealer procedures are simply “Replace part/replace transmission” and they do know actual “repair” work. If they happen to have a transmission specialist someone might be able - bit since it was in once and mis-diagnosed, it does not sound likely.

I would just put in the cheap OSS at this point and see. I believe there is a very good chance that could resolve your issue.

 

So I got a new OSS and put it on. The car drove perfectly fine and the transmission was a lot more adequate than before. Up until last night when the same P0761 error came up. I will be taking the car to the local Toyota dealership for changing spark plugs and will ask them to check the transmission again. I am open to any suggestions on what might be going on inside it. Thanks!

 

Let’s clarify something - do you have in fact a 2nd gen GS300, or 3rd Gen GS300? 2005 in the US is 2nd gen, some other markets it can be prior 2nd Gen (Australia, for example, is like that - based on year sold and not model year the manufacturer labels it).

The reason I ask is that earlier generation of Lexus has known ECU board issues. This may be a computer issue, not a hardware problem. If you swap electrical components, and the problem goes away - then comes back - that points to an electronic control issue, not an internal transmission issue. Follow?

 

Hi Oro! It is a 3rd gen manufactured in November of 2005. I'll reply back once I hear something from the dealership.

 

Can you confirm it was properly filled with the correct fluid after the solenoid was fitted?

I bought a 2005 GS430 with high miles and a misbehaving transmission throwing three solenoid fault codes. Mentioning the mileage to any transmission specialist over the phone brought immediate 'rebuild' predictions costing more than the car was worth.

I asked one shop to start by just checking the oil condition and topping up the oil. It has no dipstick, a sealed transmission and I suspected low oil due to one of the behaviours. It was less than half full! Since the top-up it's behaved perfectly.

 

Good point. - I took this for granted. I’ve seen a GS be almost 4 quarts low - AFTER a shop visit. Amazing how some technicians do not know how to properly fill and check transmissions.

 

OK, just checking. In Japan, the US, Canada UK, etc. that would be a 2006 model because of naming conventions. But I know some places strictly follow date of assembly - Australia does that I believe. Just double checking; does not change anything.

 

Obligatory "hey you have a 2006 GS300 or 2006-2007 GS430 with transmission problems, have you tried inspecting and repairing the ECU (which contains the integrated transmission control unit) yet?" ...

Lexus service bulletin:
https://static.nhtsa.gov/odi/tsbs/20...61736-2273.pdf

Repair:
https://siaelec.com/product-category...repair-return/

Sometimes you can find SIA listing their repair service on eBay for cheaper.

Also, is your GS300 a RWD or AWD model? The RWD models have a weaker transmission (A960E) and don't tolerate the abuse of a failing ECU very well.