Trans Low Fluid Pressure

[Grinder1]

Well my 07 5.9 let me down last night. Check engine light came on while towing my empty (thankfully) horse trailer. Pulled over, hooked up scanner, and got the infamous P0868 “low fluid pressure” code. Cleared code, but it immediately came back on start up. Attempted to drive on, but trans seemed to be starting in 3rd, and a slight chatter also. Fluid not burnt, but looked aerated and above the mark. Truck was NOT on level ground, so hard to say what the true level was. I know there’s been much discussion about the 48re trans and all it’s weaknesses, but haven’t had the time to delve into the latest details. Truck is currently at a Dodge dealership in OC, SoCal. I’m hoping to get some wise insights to this breakdown, before the service guy calls with their expensive “ideas”, as to what’s wrong. Help on this will be very much appreciated, as we’re in the middle of a major move (aka really bad timing).

 

[Timd32]

On my Alldata it shows that description is listed a little different then you have, the 42RLE lists it as you have it.

42RLE
P0868-LINE PRESSURE LOW

For the 48RE it's listed as: (also the overview) if you remember post up what they find.

P0868-GOVERNOR PRESSURE SENSOR VOLTS TOO HI (DIESEL)

I really have no clue just figured would look that up and see what they list.



Theory of Operation

The Governor Pressure Sensor is used by the ECM to adjust the Governor Pressure to a desired level for shifts in first, second, and third gear. If the ECM detects the monitored sense voltage is greater than or less than a predetermined specification, the ECM will set the desired DTC.


- When Monitored:

Continuously with the ignition on and the engine running.

- Set Condition:

This DTC will set when the monitored sense voltage from the Governor Pressure Sensor is above 4.89 volts for the period of 8.5 seconds

Good luck with your repair. Hope it's just a wiring harness fix or a connector, thats kinda how it lists it when it will not reset. Says to check for stuff like that. But if it does reset there is a bunch of tests and details listed.

-------------------‐-‐--------
Using the schematics as a guide, visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires.

Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals.

Wiggle the wiring and connectors while checking for any possible open or shorted circuits.

Check for any Service Information Tune-ups or Technical Service Bulletins that may apply.

 

[cerberusiam]

Probably the transducer is bad. Only pressure measured is gov pressure and it it is starting out in Drive that is a likely source of the issue. Could also be the VB harness has finally deteriorated to where it is losing readings. Usually see that if the trans control plug is pulled and it is wet with fluid.

I would have them replace gov solenoid, transducer, output shaft speed sensor, and VB harness if there is any question on it.

 

[Grinder1]

Probably the transducer is bad. Only pressure measured is gov pressure and it it is starting out in Drive that is a likely source of the issue. Could also be the VB harness has finally deteriorated to where it is losing readings. Usually see that if the trans control plug is pulled and it is wet with fluid.

I would have them replace gov solenoid, transducer, output shaft speed sensor, and VB harness if there is any question on it.

Hey Cerberusiam, always good to hear your insights on this stuff. I agree, and those parts are exactly what they’re dealing with, sans speed sensor. I was on a Rv trip 5 years ago, and had both gov solenoid and pressure sensors replaced at a dealership in Prescott. That was less than 20k miles ago, so just goes to show those factory parts don’t hold up! I wish I had the time to do this repair myself and use upgraded parts, but I’m up against a wall with our move. Truck should be repaired by tomorrow, and I’ll report how it turned out.

 

[cerberusiam]

Do not discount speed sensor, if it doesn't work correctly it can cascade down to false codes on pressure and such. If nothing else it should be pulled and checked for buildup on the end of it that will cause 3rd gears starts and weird codes. In fact, IIRC that was the exact code and symptoms we just cured on our 05 with a fluid exchange and an output shaft speed sensor. Fluid was bad but the sensor was definitely not reading correctly.