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Hello all, I need some help figuring out my CEL on my 2011 Ram (4.7, 545rfe, 100k). The original codes are P0933, and P0869 twice. I brought it to the shop to get fixed because I was hoping they could get it sorted out quicker then I could. it has been in there weeks now, started with pressure sensor, then we did a fluid and filter change, lastly the valve body was removed and the sensor was replaced (assuming it was the shift sensor). This morning on my way to work I had a hard shift from first to second and then fine the rest of the trip until I was pulling off the highway and the CEL came back on. I have already dumped a lot of money at the shop so I think I will tackle this on my own now, any suggestions? What should I look for? I should add that on original diagnostics, the transmission had high pressure at startup; was fine after that.
 

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P0869 (Line Pressure High) is pretty rare, and it's even rarer to actually have high line pressure!

I would suspect you have a bad wiring connection. P0933 in particular often indicates a line pressure sensor that is not plugged in completely. So first step would be to simply disconnect and then reconnect the LP sensor wiring, making sure the connector is fully seated and latched. You could also check for any obvious corrosion or damaged terminals in the LP sensor wiring connector.

If that doesn't help, your dealer should have a special tool (kind of like a tee fitting) that allows them to connect a mechanical pressure gauge to the trans (while the Line Pressure sensor is still hooked up). That allows them to confirm whether the sensor reading is accurate (i.e. whether it matches the mechanical gauge). So that would be the next step. If the sensor reading is bad, then (since you already replaced the sensor) I would assume the wiring or PCM is bad. Dealers also have a Transmission Simulator tool that they can plug the LP sensor wiring into. The Simulator simulates a good transmission, so they can see (for example) if (when the Simulator is set to, say, 90 psi) the PCM is actually showing a 90 psi reading. If so, then that confirms that the wiring and PCM are OK. If not, then you check resistance on the wiring.

One other possibility would be a bad control system. That is, the PCM thinks it's commanding a certain pressure (say 60 psi), but in reality it's actually driving the LP control solenoid so that you have 150 psi. Or maybe the PCM is driving the solenoid accurately, but the LP solenoid itself is bad (although it sounds like they already threw a solenoid module at it as well). Both of those would be VERY rare (I have never seen either one actually happen), but it is possible.

You should be able to find the problem and fix it without pulling the trans. The one exception would be if you have a stuck main regulator valve (which is inside the pump assy). But to get HIGH line pressure, the valve would have to be stuck CLOSED, which again I have never seen happen. I've seen dozens of stuck regulator valves, but they ALWAYS get stuck in the OPEN position (which gives you LOW line pressure), so I don't think that's your problem.

Bad wiring connection (or bad wiring in the LP sensor circuit) would be the most likely cause, in my opinion.
 

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Discussion Starter #3
thank you for you help, i will try to check the wiring my self and see if i can find anything.
 

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So last night I had a new string of problems;

Will not go into overdrive or possibly last two gears. Driving the highway was next to impossible, 55 is even a challenge. My thought was limp mode but from a stop I can feel it go up through the gears (3rd or 4th)

I tried tow haul mode and it lit up but I couldn't feel a difference, it's like it's not working.

Next I tried to manually down shift and the indicator was cycling fine through the gears but it was not actually changing the gears.

I had to make a stop and left it running, when I shifted into drive, that's when it went to limp mode (indicator displays 4). I drove to the local advance auto to run the codes and the clerk told me the p0933 was the only code this time.

Does any of this help narrow it down? Could it still be electrical or is it pointing more towards a problem with the valve body? Could a bad pcm cause these shifting problems?
 

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So last night I had a new string of problems;

Will not go into overdrive or possibly last two gears. Driving the highway was next to impossible, 55 is even a challenge. My thought was limp mode but from a stop I can feel it go up through the gears (3rd or 4th)

I tried tow haul mode and it lit up but I couldn't feel a difference, it's like it's not working.

Next I tried to manually down shift and the indicator was cycling fine through the gears but it was not actually changing the gears.

I had to make a stop and left it running, when I shifted into drive, that's when it went to limp mode (indicator displays 4). I drove to the local advance auto to run the codes and the clerk told me the p0933 was the only code this time.

Does any of this help narrow it down? Could it still be electrical or is it pointing more towards a problem with the valve body? Could a bad pcm cause these shifting problems?
Hard to say, but with P0933 the first thing I would do is make sure the LP sensor connector is fully seated and latched. The LP sensor is on the passenger side of the trans, at the very back of the main case, just above the oil pan rail. There is often a heat shield covering it. Check that wiring.

Next step would be for a dealer or shop to check the LP sensor reading and see what it's doing (bouncing all over the place, or stuck on one constant reading, or actually stable and following the Desired LP value like it's supposed to).
 

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just a little update, I my self could not visibly find any problems with the wiring, my shop ran their test and assured me the trans was toast so we found a good price on a used one with a warranty and the shop put it in. unfortunately the same problems remained after the trans swap my mechanic threw in the towel and brought it to the dealer. The dealer could not find what was causing the problem so they turned to Chrysler who said it would be the pump in the transmission causing the problems so now we are going to try a 3rd transmission and see if maybe the 2nd just happened to have the same problem as the original. The good news I haven't had to drive my truck in the salt this winter.
 

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just a little update, I my self could not visibly find any problems with the wiring, my shop ran their test and assured me the trans was toast so we found a good price on a used one with a warranty and the shop put it in. unfortunately the same problems remained after the trans swap my mechanic threw in the towel and brought it to the dealer....
Sounds like (sure enough) the problem was not in the trans. And it still isn't.
 

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2011 Ram 1500 SLT 4.7 254k 4/4/21
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I'm replying to this post Because, I too have this issue but P0934. Line pressure sensor circuit low. I'm going on a Year now with this persistent code since I had a " reputable" shop Do a full overhaul when my OEM Transmission detonated at 237K The Shop I used had my truck for over 4 months, changing PCM, sensors, Re-learn performed, you name it... Finally I said rebuild it or I'm taking action! I was given every excuse in the book. I even took it to another shop to get a second opinion because the original shop was claiming it was my " aftermarket lightbar " causing issue... That must of been a joke, from the owner who was swiftly reprimanded by the son who asked I not speak to his kooky old man! Anyways, @TransEngineer Thank you for the info, I'm assuming this 2nd rebuild performed didn't include inspection of pump assembly? They assured me all was new, then the story went new heavy duty clutch packs and torque converter. Its still under warranty and i currently have 254K On the odometer, Come to think of it its time to call them up for the information they keep saying their too busy to send over. I request a print out of Parts and part numbers replaced, along with the tech who performed the Flash on the PCM. After the first time he performed this action i was given my truck back with out working dash lights and no tow/haul response from button... all very frustrating but ill be sure to get what i paid! Thank again boys
 

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P0934 indicates a problem with the line pressure sensor, or the wiring for that sensor, or possibly with the PCM itself (if it isn't correctly reading the actual sensor voltage, which I have never seen happen). It is NOT anything internal to the trans!
Replacing or rebuilding the trans for this code is like, "Your coolant temperature gauge was showing "Cold" all the time, so we replaced the engine."
 

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2011 Ram 1500 SLT 4.7 254k 4/4/21
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The man, the myth, the legend, @TransEngineer. After all this time reading forums, gathering this that and the other. I’ve reached the pinnacle, and received the humbling perspective metaphor response only a few of us are Gifted. All jokes aside, how did you know i just swapped out my coolant temp sensor?

Alright, so I’m listening! I’ve don’t my fair share of rolling under the truck, visually inspecting sensors, grounds, the wire harness from front to back, hoping to locate a loose connection or damaged portion or anything, obvious before i grab my meter. Or pay to have electrical diagnostic performed of said area. I assume low line pressure isn’t beneficial for these 545REF units? I have an OBDlink MX+ which i use to monitor DLP comparative to ALP. As found data is intermittent and reading your previous responses above, my DLP never changes from 125PSI. Only once and this was a recent road trip i was monitoring the DLP while cruise control engaged, and it displayed 50PSI.

Now this line pressure issue/CEL code P0934 i have is also intermittent. Some mornings while warming my truck up i get the JScan app going and monitor DLP and ALP on the way to work. On good days truck runs strong, ALP: 136psi & DLS: 125psi. On other days, mainly after work or stopping off somewhere and turning the truck off and back on. I can feel the way the truck drives is completely different. Usually the next day I’ll get the CEL when i start my warm up. On the days the truck runs noticeably different my DLP stays at 125psi while my ALP is all over the the range. 48-128psi...I’ll attach a screen shot to show duty cycle % and LP A/D input pressure. I have some screen recordings as well...

I feel the end of this tedious Problem may be insight, with your input and the data I’ve collected, i need to determine my next move. Thank you again for a quick response!
606CDF20-5042-489A-AC5A-00539D890731.png
 

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Actual line pressure should track Desired Line Pressure (DLP) within a couple psi. In your screenshot, if LP = 136 and DLP = 125, then I would expect the PCM to raise the duty cycle (from 16.1% to some slightly higher value) in order to bring the LP down to the 125 psi target.
If your DLP is reading 125 psi all the time, then I suspect your scan tool is using the wrong PID for that value. DLP should vary with torque (throttle), gear, and other factors.
But the issue with P0934 is not the DLP (or actual LP) at all. The LP sensor has limits on its voltage; I believe the low limit is 0.35 V while the max is 4.75 V. The sensor voltage should never be below 0.35 V (which corresponds to a pressure reading of 30 psi). That's why, if you turn the key on / engine off and check the LP reading, you should see 30 psi (even though the actual pressure is zero). P0934 means the PCM saw LP sensor voltage below 0.35 V, i.e. less than the sensor should ever read. This could be due to a bad sensor, or a broken / poor connection in the wiring.
For starters, I would just monitor the LP sensor voltage and see how it's behaving. High voltage = high pressure. See if the voltage is stable (while the DLP is stable) or glitching around. See if there are any times when the reading is zero volts.
 
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