48rfe p0868 code

[Kawierider]

Hi guys,

I've been lurking around here for awhile, and though I haven't had much to add, I'm hoping to talk through a recent issue I'm having. Sorry in advance for the long post. The devil is in the details!

Heres the situation:
2004.5 ram 2500 Cummins HO automatic trans, 4wd. Stock except 35x12.5 tires. 170kmiles

trans was replaced at 125k with a factory mopar unit in 2010.

i noticed two weeks ago that the engine was running 2krpm at 70mph (on speedo). I don't drive the truck regularly, so I thought it seemed high but everything else seemed gtg. So I went on with my weekend.

this last weekend, I drove up north. Loaded only with a 1500lb pop up truck camper. On the way home, after cruising 65mph for about an hour and a half, I noticed that my tach was swinging ~200rpm frequently.

The issue seemed to improve when I slowed down to 60, but didn't go away completely. Tach reading 1800-2000rpm. At 70mph, things seemed fairly happy.

One other event of note: during one of the periods at 65mph when the rpm was oscillating, I had to accelerate because of merging traffic. The trans down shifted what felt like two gears. Tach swung up to nearly the red zone for the split second it took me to back out. The truck seemed to up shift and continue on.

No cel light through all of this.

This is evening, I put my torque scan tool on and I received a check engine light with the truck idling. P0868. I suspected a Tc lockup issue might be related to the tps so I set up a line chart and swing the pedal (truck not running) through a few slow pedal sweeps. Nothing seemed jumpy or abnormal.

I know this p0868 code is low trans line pressure (correct?).

my thoughts on root cause:
plugged filter (scary- clutch material?)
line pressure sensor(seems common)
line pressure regulator(think the sensor and regulator come together?)

my plan was to change fluid and filter tomorrow, and if that doesn't solve the problem, either just replace the other two components or hook up with a friend who has acces to a line pressure gauge and a scan tool capable of reading demand pressure , then changing them once I've verified. Only advantage to doing this is if I have a Pump problem, I'll know before I waste money on the control parts.

-thoughts?
- have I missed anything?
-any resistance checks for either the solenoid or the sensor that can be performed externally?
-What are the odds that low line pressure has caused my od clutches to slip and burn up?
-same concern for the Tc lockup clutch?
-anyone think I can talk the dealer into honoring a 3yr/100k warranty even though the three years have passed!?

Thanks in advance!

 

[cerberusiam]

To start with your truck does not have a 48RFE transmission, that model does not exist. Your truck has a 48RE transmission. Secondly, there is no monitoring of transmission pressures on a 47/48RE transmission, any codes that reference such are nuisance codes. The only pressure monitored on a 48RE is gov pressure. The P0868 is a 45RFE code and not applicable to your truck. When it does show up it is because of a glitch in the OBD reporting functions which are pretty lean anyway. The 03-04 trucks suffer from a lack of and consistency in what the codes really mean.

70 mph with 35" tires should net a little less than 1800 rpms cruise at 70 mph, IF your tire size has been corrected. If that hasn't been done then all comparisons are invalid. 200 rpms at 70 mph could be a bad TC, a bad cluster, or just invalid info from the ABS module.

Driving experience will be a better source of function. Do you feel the TC lock? Does it feel locked when you blip the throttle at road speeds (it should feel like a manual in gear at speed)?

Clusters go bad, your truck is 13 years old so failure of some of the common pieces is expected. If the tach or speedo vary at steady throttle and you cannot feel the surging likely the problem is the cluster.

 

[Kawierider]

Thanks for the response: typo with the 48rfe/48re.

the speeds listed are speedo speeds with uncorrected speedometer: as far as the truck knows it's the same as the stock tire size, but with slightly higher load.

I could hear hear the truck hunting for rpm

i also should add fuel level correct. Not burnt.

Symptoms did did not repeat yesterday when I drove the truck on the freeway (same camper load as this weekend)

I put out the truck on a friends scan tool. The demanded governor circuit pressure matched the actual measured pressure at low speeds. At freeway speeds however, the demand was around 127psi. Actual was lower between 85-105. During this time the control percentage was 1. I believe this to mean the control system was demanding the pwm gov solenoid 100%closed.

In in my mind this means either 1) governor regulator is not functioning correctly or the pump pressure is not adequate. I believe 1 means that the valve was closed trying to raise the pressure (anyone know which way this logic works? )

This seems to make sense with my violent downshift if the governor circuit is what disabled the downshift ability to specific gears at speed (the shifts I believe are achieved through differential pressure between line pressure and gov circuit pressure).

The remaining question that I can't answer: how would gov circuit pressure affect lock up or od clutch pressure. Assuming my oscillations were caused by either a unlocking Tcc or a slipping clutch.

Also: what should pump pressure be during operation 1800rpm/65mph?

does the gov regulator valve dump fluid from the gov circuit to pan?

If if that is the case it might make sense that if it was stuck open and dumping excessive fluid it could affect line pressures intermittently?

 

[cerberusiam]

The uncorrected speedometer is messing with the trans controls to a point along with the TV cable possibly being a little to tight. That will definitely cause a downshift at speed it should not. Going WOT will also set the system into a dither mode at times and you get some weird reactions if every thing is not perfect. Training the right foot to not go WOT until over 70 mph will eliminate a lot of that.

Once OD is engaged the gov pressure is maxxed out and no longer has any effect on shifting and is essentially ignored until the TCM decides to drop it out of OD. When it does drop out of OD at those speeds and WOT throttle it takes a few seconds to reset the balance in the gov\TV system. If the transducer or gov solenoid is compromised in any way it takes longer to react. The stock parts are wear items, about 30k and their functionality starts to waver and readings drift. The control system is really pretty crude on a 48RE and just not very smart. The stock profiles are geared toward NVH not good operations.

Stock pressure around 1600 rpms are usually in the 120-125 psi range so a demand of 127 in OD is not far enough off to worry about and the TCM will simply ignore the issue.

Most of us toss the stock transducer, gov solenoid, and gov housing in favor of better parts then add a shift kit to compensate for the NVH induced laziness in the trans operation. That along with the ability to now tune some of the parameters it fixes a lot of the little glitches. The 03-04 trucks are pretty limited on trans tuning though, some times it takes modding the operation of the VB to tune it.

 

[Kawierider]

I follow what your saying. It makes good sense.

To to elaborate on my concern further:

if my demand (what the ecu wants to see) in the gov circuit is 127psi, and the pressure sensor is only seeing 89, the computer should be increasing or decreasing (not sure which way it is set up) the pulse width applied to the governor solenoid valve. Under this condition the measured pulse width was basically 0% which sounds correct if an unpowered valve would raise the gov circuit pressure.

The concern: if my governor regulator valve is unpowered, or to put it another way commanded closed, in theory, the circuit pressure would match the feed pressure (maybe minus a few psi for leakage). Following this logic, there are three root causes for the condition that I can think of 1) solenoid valve leaking, not allowing pressure to build in the circuit 2) bad sensor outputting a pressure lower than reality 3) low pump/valve body pressure (closing the regulator valve won't matter if the input is low)

i can eliminate 1&2 by swapping the parts so I'm planning to pick up the Borg Warner solenoid valve and oe sensor tomorrow. Will also do filter while I'm in there.

as far as number three low line pressure as I understand it would mean a weak lock up of the Tcc and all of the clutch packs. I think I'm talking myself into symptoms, but I've had enough mildy strange behavior in the last three weeks that I'm nervous.

The other two strange instances: I was backing my truck/1500lb truck camper up onto a set of 2x12's required maybe 30% pedal with only the truck camper, and a second instance where I briefly towed a 28ft 6500lb camper from one camp site to another and while pulling in the tail of the camper dragged on a hill. Hard enough to make deep ruts with wheels under the rear bumper. I stopped and when I went to pull forward I put nearly three quarter pedal into it and when boost started building I let off. No tire spin, no movement. I backed up just fine in 2wd and pulled forward in 4 low with no difficulty whatsoever. It was just...strange...enough to make me wonder why it didn't spin the tires on the dirt. (Thinking now this may have been an involuntary second gear start or slippage....or just finding reasons to be paranoid!)

I guess i also also need to find and install a pressure gauge in the system and check line pressures to be sure I'm not missing anything. Thanks for the info on the pressures, I also need a good manual too.....

 

[cerberusiam]

The only caveat to what you are thinking is in OD the gov circuit is flooded with apply pressure when the OD solenoid opens. At that point the solenoid is just demanded wide open and the ECU isn't trying to correct, it just is what it is. The only time the gov pressure is actively trying to adjust is when OD is disengaged.

The stock transducer and solenoid are junk, they just don't last long enough for the cost. The best solution is the DNC gov housing with the GM style solenoid, should be the last one of those you buy. The gov housing itself has issues with sharp edges and turns that tend to grab and hold sludge causing problems. The DNC piece gets rids of the problem areas and opens the circuit for better flow and cleaning.

FSM and an ATSG manual will be your best friend, that pretty much has all you need to dig thru the truck in general and drive train in particular.

 

[promisedland]

Following along,.. Cerb; you have brought it up before that the 48RE dosnt like WOT as it messes with shift logic, now you say again... so, do i put a board UNDER my thottle?
Explain some please? Thanks

 

[Kawierider]

Cerberusiam,

that at one caveat may be a significant one!

I only saw saw that demanded governor pressure was low at free way speeds, when od (and the solenoid) should be engaged. I did see that the ecu was not controlling....simply along for the ride at that point.

I just installed the BW solenoid valve and the new sensor, and new filter. I also adjusted the bands(figured it wouldn't hurt while I was in there). Filled to the correct fluid level. The truck feels fine in 1-3, but Now I'm not getting any OD at all. The code is still active after being reset.

I guess the logical place to go from here is the od solenoid jumper, is there a more logical place to look given the one and only code is the p0868 code, and the truck otherwise seems to drive fine?

 

[cerberusiam]

so, do i put a board UNDER my thottle?
Explain some please? Thanks

Right foot training not to go WOT until rpms speed and boost dictate. Until boost hits 30 psi is simply is not going to fuel any hard than the tables indicate, 3/4 throttle or WOT really makes no difference until the table driven parameters allow it.

I guess the logical place to go from here is the od solenoid jumper, is there a more logical place to look given the one and only code is the p0868 code, and the truck otherwise seems to drive fine?

I looked that code up in my FSM and it is Gov sensor voltage high. If you are still getting that code there is a good chance the VB harness is shorted somewhere causing the issues. Gov pressure problems will cause loss of OD activated by the TCM yet if you put a switch on it there is no mechanical issue. My guess is if you solve to code issue OD will start working again.

 

[Kawierider]

Thanks. Looks like the harness for the governor pressure sensor and the solenoid are included with the od/Tcc solenoids. So I guess As soon as it stops raining here, I'll disconnect ecm, check for shorts in the outside the trans harness, do some resistance checks, and put in a new od/Tcc solenoid/harness. I'll also see if the resistance across the old sensor and new one is the same.

 

[Kawierider]

Update:

No 12v to the transmission connector(key on running)
good continuity from tcm relay
12volt into relay with key off
12volt into other relay pin with key on.
7kohm resistance at ground pin to neg bat connector.
.4ohm from ecu pin 31 to relay ground pin.

Swapped relay lay with the wiper relay. Wipers still worked ( maybe slow?) still no 12v to trans connector with engine on.

Jumped the relay. Have 12 volt at the trans connector now.

Everything points to to a bad trans relay, but swapped and no change!?

Is 7kohms through the ecu abnormally high?

 

[cerberusiam]

Just about all the systems are monitored for 5 to 100 ohms resistance. 7 ohms is in the range and on the good side.

Sounds like you have a connection problem in the socket where the relay sits. It is not unusual that corrosion will destroy the PDC and FCM at the connections.

 

[Kawierider]

7kohms not 7ohms. I'm thinking now that it's a mistake to test that resistance with the relay out....the ecu would shut that ground pin off.

Will recheck through the insulation. And replace the relay for good measure

 

[Kawierider]

7kohms not 7ohms. I'm thinking now that it's a mistake to test that resistance with the relay out....the ecu would shut that ground pin off.

Will recheck through the insulation. And replace the relay for good measure

I replaced the relay today. No change in symptoms. I was able to pull relay up slightly in the socket and get 14volts on pin 87.

I pulled connector c2 from the ecu. Measured:
pin 87(relay) to pin c2-14 ( gov pressure signal) -4.5ohms

pin 87(relay) to pin c2-15 (od shift solenoid) - 34.6ohms

pin 87(relay) to pin c2-25(Tcc solenoid) -34.3 ohms.

c2-23 to c2-18(gov press signal)-151kohms)

c2-24 to c2-29 (trans temp signal) - 1.19kohms

for reference: the pressure sensor I pulled out had 18kohms across one circuit and open circuit across the other. That likely explains the original code.

I I hate to say it, but I think ill have to load test the circuits, I think to go any further unless someone tells me those resistance values for the solenoids are way off. The only other thing I can think of is something hung up in the valve body.....

all the electrical connections look good to me. Very clean no corrosion. Doesn't mean there isn't a problem lurking, but......I guess that's the only thing I haven't really checked.

 

[Kawierider]

Ok!

Overdrive is back. Went in to swap the od shift solenoid today and the third bolt I removed was "fingers coated in atf right" took at least 5 rotations before it was back in enough to engage the od shift solenoid plate (transfer plate?) again. Explains all the behavior...and no, I never even touched it my first time in there!

Electronics doing what was intended, but no ability to build hydraulic pressure.

I still ill doint seem to have od, but now I was able to dump the black water tank on the camper so I can remove it and make sure the pedal position isn't the cause (don't think so, but hey). Could also be that the mounting plate for the two solenoids is warped, so I'll check it with either a scan tool or a Tcc lockup switch after the camper is off.

Creating strange failure modes one Memorial Day weekend at a time!