Lexus LX450 - Transmission - Shift Solenoid Electrical Code (1 Viewer)

[CJK]

Hi all,

Long-time Lurker, finally running into an issue I haven't been able to solve either on my own or with the help of the "Search" button on the forum.

I have a stock Lexus LX450 with 176K miles. I recently added a center diff switch and performed the 7-pin mod, as well as replaced the center console/subwoofer/CD player with a Smilty Built center console.

About 100 miles (1 week) later, the CEL turned on and O/D Off flashed, indicating the transmission is experiencing the error. The symptoms were transmission in limp mode, which felt like only 3rd Gear in Drive, or 1st Gear if I was in Low.

I pulled the CEL code and it showed P0753 - Shift Solenoid Electrical. I double-checked all the connections to ensure the connectors were seated properly, which they were. I checked Center Diff control unit in driver kick panel, the Center Diff switch behind dash, TCU behind glovebox, and the wiring under shifter bezel). I thought the Center Diff Switch + 7 Pin mod were the problem, so I reverted the 7pin mod, which made no difference. I did not revert the Center Diff switch.

Since it didn't seem like an obvious issue, I checked the forum where I learned the A343F transmission has known issues with solenoids failing around 150-250K miles. Since correlation does not equal causation, I thought maybe the solenoids did actually fail. I used the FSM to walk through the steps to trouble shoot that code, which had me unplug the TCU and check Shift Solenoid wires for impedance. Neither measured the proper resistance. Then I checked connectivity of wire from TCU to Transmission housing plug. Since that was all fine, the FSM suggested I replace the Solenoids.

So, I dropped the pan, replaced the solenoids (and filter while I had the pan off). The fluid didn't look terrible, but definitely was worth draining and cleaning out the pan. I used the Toyota FPIG to seal the pan back up and added 1.5 gal of ATF back into the transmission.

When I started it up after, the truck ran fine for a few minutes, then threw the CEL again after driving about 3 miles.

It was already 5pm so I called it a day, but now I'm not sure what could be causing the code to get thrown. I'm kind of out of ideas at this point until I re-look at EWD, but was hoping someone else has experienced this or might be able to help ask the right questions that could help.

Any ideas?




Appendix:

Electrical Connections that were touched:

1) Center Diff Switch (Removed stock ground connector, installed Center Diff Switch)
2) Center Diff Control Unit (Removed connector, removed wire in 7 slot, taped up wire, plugged back in)
3) Subwoofer (Removed, connector is unplugged)
4) CD Player (Removed, connector is unplugged)
5) 2nd Start / PWR (Removed connector, plugged back in. 2nd Start functions)
6) Shift Lock (Disconnected to route wires, reconnected)
7) Some sensor under shift bezel located forward of the 2nd Start / PWR buttons (Disconnected to remove shifter bezel, reconnected)
8) One more connector under shift bezel coming from shifter (Disconnected, but reconnected).

 

[shocktower]

Ok you need to unplug your transmission and drive it and manually shift it, through the gears, and if it shifts it maybe the solenoids ( I have dealt with many 343 and 442's the 442 has more solenoid issues ) ,now before plugging it back in spray your plugs with Deoxit both male and female . Now check the kick down cable and make sure it is good order and adjusted properly. After all of this it should solve the problem OH yeah check the TPS throttle position sensor for it's adjustment, Oh yeah what solenoids did you buy ??

 

[CJK]

Awesome, thanks for the help, shocktower. I will do those and report back, it may a few days as I've got several things coming up that I need to take care of for work.

I bought "A340E / A343F Transmission Master Solenoid Service Kit 1994-1999" from Cascade Transmission Parts (LINK) and used Toyota FPIG to seal the pan instead of the rubber gasket.

 

[CJK]

Hey Shocktower, following up here now that things have calmed down.

I unplugged the connector to the solenoids at the transmission housing and manually shifted it through gears without any issues. After that, I did spray both male and female connectors with contact cleaner.

Kickdown cable checked and it did not need adjustment.

I checked TPS and at idle was at 12% where spec said 10% so I can adjust slightly, but only small amount.


I'm still inclined to believe it's an issue with something electrical, so when I am back in a couple weeks, I will check the connections to the ECM and TCM.

 

[Tools R Us]

Have you unplugged, inspected the connection of the engine harness to transmission harness (EC2) near/over the starter?

 

[CJK]

I have not checked that, yet, but that's a good call out. While I'm down in 29 Palms, I'm trying to make a list of things to check on as I've already followed the FSM procedure for that Error code and it did not resolve it.

 

[CJK]

I checked the electrical connections yesterday and don't think that's the issue. I have continuity between the solenoid wires going into ECU and the wires plugging into Trans. Furthermore, I measured 13.5 ohms for each solenoid.

At this point, I don't what else to do so I'll be taking it to someone professional. I called a local place that specializes is Toyota Trucks. He did ask if the A/T Temp light came on when the car went into fail safe mode the first time. I believe it did, so he thinks it's an issue with the valve body, which would need to be be replaced.

If that's the case, I'm contemplating upgrading from a replacement VB to an upgraded WAT Nomad VB. I can't seem to find a cost for a replacement, but the WAT are $1300.

 

[CJK]

I called Georg and he recommended trying a different ECU, as he's seen the ECU causing strange issues before. I bought one from the classifieds section for $110, so I'll give that a try. If not, to the transmission shop I go

 

[CJK]

No luck on the ECU fixing the problem. Vehicle has been at shop for the last 3 weeks without a solution. They've looked at the wiring, the solenoids (again), even replacing the valve body, but nothing has fixed it. They haven't given up, but are recommending the next COA is to replace the transmission.

Anybody have any other thoughts here? 176K seems awfully low to replace the trans, any tips of acquiring a new one without breaking the bank?

 

[shocktower]

No luck on the ECU fixing the problem. Vehicle has been at shop for the last 3 weeks without a solution. They've looked at the wiring, the solenoids (again), even replacing the valve body, but nothing has fixed it. They haven't given up, but are recommending the next COA is to replace the transmission.

Anybody have any other thoughts here? 176K seems awfully low to replace the trans, any tips of acquiring a new one without breaking the bank?

Ok like I said before Dexoit the plugs, and then it sounds like your neutral switch maybe bad, I have 290K on my 343 and the last 60K has been with a 6 BT Cummins, and I drive it every day. So go back and use Deoxit and clean them well, also check the neutral switch again, you are having a simple electrical problem, don't throw parts at it, narrow it down

 

[CJK]

Shocktower - I 100% agree that the transmission should not have to be replaced. They just don’t know what it is, so they’re using the shotgun method to fix it. I wasn’t planning to have to replace it anyway, I’ll take it elsewhere if needs to be done.

I’m going to get the vehicle on Monday and will go through electrical connections again with contact cleaner. To your point, I did use contact cleaner on the terminals to the solenoids. But i’ll Print off a copy of the EWD and detach + spray all the connections involved in the trans.

 

[CJK]

It's been a while but wanted to follow-up in case someone in the future is experiencing similar issues with their transmission.

I took the vehicle to a transmission shop recommended by Georg (Valley Hybrids) that was in my area. They looked at it and diagnosed an electrical issue.

They ended up pulling the front fender off to gain access to the wiring harness on top of the transmission. In there, they found that the wires to the solenoids were frayed from abrasion. While they were not completely severed, they were not allowing for adequate power from ECU to Solenoids, which was tripping the CEL

 

[taylort232]

It's been a while but wanted to follow-up in case someone in the future is experiencing similar issues with their transmission.

I took the vehicle to a transmission shop recommended by Georg (Valley Hybrids) that was in my area. They looked at it and diagnosed an electrical issue.

They ended up pulling the front fender off to gain access to the wiring harness on top of the transmission. In there, they found that the wires to the solenoids were frayed from abrasion. While they were not completely severed, they were not allowing for adequate power from ECU to Solenoids, which was tripping the CEL

What do you mean the front passenger fender? The plastic insert, the fender flare, or something else?

Thanks!

 

[CJK]

What do you mean the front passenger fender? The plastic insert, the fender flare, or something else?

Thanks!

front passenger fender.

To my recollection, they removed it for better access to the wiring for ease of diagnois and fixing.