Help !!!! - Code: P0748 – Transmission Fluid Pressure Solenoid

[GSANDERSON]

Hi All,
New on the forum and looking for help with a problem.

Riddle me this, guys and girls —
I’ve got a 2008 4.5L V8, and it’s throwing up some dash lights and error codes.

Code: P0748 – Transmission Fluid Pressure Solenoid

It’s causing 1st gear to be non-existent, and it seems to default into 4th gear as standard. I’ve got an OBD reader, and when I’m on the motorway I can clear the code — if only for a split second — and it’ll shift out of 4th (to what I assume is 6th) The codes come straight back up, but it stays in the higher gear.

If I pull the gear selector over to manually change gears, it defaults back to 4th and won’t let me go any higher manually.

I’ve had it at a couple of garages and even had the solenoid replaced, which we assumed was the issue (see picture). Still no difference. I had a second garage check the auto box, and they confirmed all the solenoids are working fine.

They’ve suggested it could be a wiring issue or potentially an ECU fault.

Has anyone come across this before? It’s a right pain in the arse trying to get it sorted.

Any help or advice would be greatly appreciated!

 

[GrouchyTech]

New transmission.

 

[linuxgod]

My next guess after a solenoid would be a cracked valve body. Tundra guys see these occasionally. That’s not guaranteed, just a likely problem spot, it’s possible there’s another issue causing the fluid pressure code. Apologies I would look up the troubleshooting steps for that code but my FSM is offline this week. The error codes are sensors detecting problems and the FSM will have likely steps to diagnose, but the FSM can’t account for every failure scenario either.

You don’t say the mileage but given it’s a 2008 I’ll assume it’s 200k+. Practically speaking if you’re swapping the valve body and solenoids you’re getting into $2k+ territory, at least here in the US, and there’s no guarantee that will fix it. Also driving when the solenoids are failing can cause a LOT of wear on the transmission clutches very quickly. That’s why the transmission is refusing to shift - it’s trying to preserve itself from grenading. Forcing it into gear is likely very bad for it.

If you’ve swapped the solenoid in question and are still saving issues, sadly your best bet is to pull the transmission and have someone rebuild it. In the US it’s easy to source a genuine Toyota remanufactured unit for about $3500 including the torque converter and all new clutches/brakes.

 

[riffman12]

you guys are scaring me with all these transmission threads.

I have a bit of a harsh shift from 1st to 2nd when cold, but I'm seeing more of these failures pop up.

 

[linuxgod]

There have definitely been a few posts recently.

Pretty sure I did mine in on the rock garden after The Wall on Poughkeepsie. I think one particular hit did something to a solenoid - I didn’t hit the transmission or skid, but I did slide off a rock onto the frame (I think). It went from “working fine” to “2nd gear downhill is like being in neutral”, which is not how I’d expect a bad clutch to show itself as failing (typically you get noticeable slippage that grows over time).

I haven’t seen mileage on this one but it’s a 2008.

 

[GrouchyTech]

There have definitely been a few posts recently.

Pretty sure I did mine in on the rock garden after The Wall on Poughkeepsie. I think one particular hit did something to a solenoid - I didn’t hit the transmission or skid, but I did slide off a rock onto the frame (I think). It went from “working fine” to “2nd gear downhill is like being in neutral”, which is not how I’d expect a bad clutch to show itself as failing (typically you get noticeable slippage that grows over time).

I haven’t seen mileage on this one but it’s a 2008.

Is it only your second gear that is affected or are any of the other gears acting up? Is this issue happening ONLY while in S mode?

 

[bludool]

Curious? Where can one obtain a transmission for $3500?

Have an ‘08 with 193k and developing some cold trans “slipping” issues. No codes on scanner, but expecting something. Bought vehicle from a friend. Has been very well maintained. Planning on keeping for a while.



Thanks

 

[linuxgod]

Pretty much any local dealer will sell them with a TC for $3500, give or take. Install is another $3000