Persistent P0773 Code

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Apr 18, 2022 | 10:32 AM

1uzswap

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From: CA

Persistent P0773 Code

Hi folks, let me start by saying that this is an awesome forum. I have been reading/lurking anonymously for a few years now! But I've hit a wall with this issue, so here I am, newly registered asking for yet more help

The vehicle:

Toyota truck with a 1UZ
Engine: 95 LS400
Trans: 95 SC400 (A340E/30-40LE)
CA smog legal since 2016, no issues until recently

The problem:

Code P0773 (Shift Solenoid 'E' Electrical Malfunction)
Can be cleared by my scanner (Blue Driver bluetooth unit) but the scanner will see it again immediately
CEL will stay off until the next start
Driving behavior:
- Decent power/shifting
- No lockup (terrible mileage)
- Hard shifting when coming to a stop

Brief history:

Found trans fluid in the radiator (integrated trans cooler sprung a leak)
No evidence of coolant in the trans
Had radiator fixed (by a shop)
I flushed the block with hot water, reinstalled radiator
I installed an external trans cooler
I topped up the transmission with 2ish quarts of T-IV
Get code P0773 on startup

Relevant posts:

Another truck swap with same code - https://www.clublexus.com/forums/ls-...l-bad-ecu.html

Unsuccessful attempts at fixing:

Had a trans shop replace solenoids 3 and 4 (Rostra brand parts)
I re-capped 2x ECUs (by myself), following the forum recommendations
- 89661-50231 - My trail spare, throws an intermittent P1600 code, but other than that, the truck used to drive fine
- 89661-50234 - Supersedes the 50231, and had noticeably better shifts before the radiator problem
Ran new wires for solenoid 3, from the ECU direct to the transmission connector, (used OEM Lexus pigtails to ensure a good connection)
Applied 12V to solenoid 3, confirmed it is actuating
Tried another 95 ECU at the wrecking yard
- I was looking for an "unopened" eco to send for professional repair
- This one has no factory label and has been painted in silver, so I'm assuming it's a "refurbished/reman" unit
- Seems to drive better than the 50234, but I can still hear the occasional "thunk" coming to a stop

Where I'm at now:

Try an OEM solenoid(s)? ($$$)
- FSM spec (1994 SC400): 3.5-3.9 ohms (can anyone confirm that 95 is the same?)
- Rostra spec: 5.3 ohms (https://rostrapowertrain.com/products/52-0400/)
- Measured: 5.3 ohms
Would it be dumb to wire up say, a 3.6ohm resistor to the ECU?

Thanks in advance Lexus gurus!

Last edited by 1uzswap; Apr 18, 2022 at 10:34 AM. Reason: L

Apr 19, 2022 | 09:13 AM

CLLEXUSS

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Joined: Jul 2019

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From: CA

It is an interesting problem. When I used to work at different shops, transmissions were not something generally we tore apart on a table to fix and repair, even at dealerships I have worked. It's a specialized field, though if you specialize in them they are not that difficult once you understand them, just like anything else. You can spend a lot of time with a transmission but you may never know what's going on inside it until you completely break it down on a table. It's entirely up to you but I might try to see if I can find another transmission for a reasonable price that is believed to be good and swap it out. If anything it is sort of a process of elimination. Or just keep trouble-shooting if you don't want to make that leap. It's not going to be easy for anyone to online trouble-shoot with you without being there, there's so much going on here.

Apr 19, 2022 | 09:23 AM

CLLEXUSS

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From: CA

You have no evidence of coolant in the transmission, not that you can see, but if it did get in there most certainly it could easily cause major issues. I ruined a good 4Runner auto-transmission river crossing one time in approx 4 feet water river depth, learned the hard way that transmission do not not like any other fluids besides transmission fluids lol.

Apr 19, 2022 | 09:40 AM

timmy0tool

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From: 714/949, SoCal

just a thought but bypass the transcooler for now and see what happens. my thought is that the cooler is adding unnecessary pressure/temp changes to the trans.

since you have aftermarket solenoids in there reading higher resistance, it's worth a shot to try and lower it to FSM spec (maybe doing the inline resistor as you mentioned) but i would try to find a used OEM solenoid first. search car-part.com or your local pick a part and pull it off yourself! there are many LKQ yards with LS400s in the greater socal area.

Apr 19, 2022 | 09:52 AM

1uzswap

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From: CA

Quote:

Originally Posted by CLLEXUSS

Quote:

Originally Posted by CLLEXUSS

Indeed... I've always been a manual guy - this is my first automatic and I feel like a total noob!

Forgot to mention this in the original post, but per your comments, I was all but ready to give the transmission shop the go ahead to do a tear down, but the owner/boss advised against it. He essentially said that despite the timing of the radiator issue, he still suspected something electrical based on what he could see and due to the "custom" nature of the vehicle... So I'm not against it, just trying to be patient and rule out any/all other possibilities...

Apr 19, 2022 | 10:07 AM

1uzswap

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From: CA

Quote:

Originally Posted by timmy0tool

just a thought but bypass the transcooler for now and see what happens. my thought is that the cooler is adding unnecessary pressure/temp changes to the trans.

You know, I had the same thought and mentioned that to the transmission shop, but they weren't concerned about it. Maybe time to revisit that!

Quote:

Originally Posted by timmy0tool

since you have aftermarket solenoids in there reading higher resistance, it's worth a shot to try and lower it to FSM spec (maybe doing the inline resistor as you mentioned) but i would try to find a used OEM solenoid first. search car-part.com or your local pick a part and pull it off yourself! there are many LKQ yards with LS400s in the greater socal area.

No joy on the resistor, I gave that a shot last night (actually twice, first with a 3.9ohm power resistor, and again with some misc resistors in parallel that were equivalent to 3.5 ohm according to both my math and the meter...)

OEM solenoid might be the next step, need to make some time for a trip to the yard

Apr 19, 2022 | 11:26 AM

Losiracer2

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Joined: Sep 2008

Posts: 1,286

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From: Chandler, AZ

I had this same code on my 97' and just went and got a JY OEM Lexus solenoid off a SC300, anything with an A340E should work. Did the trick and code or the shuddering never presented itself again.