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  #1  
Old 10-13-2012, 03:05 PM
leejeffcoat leejeffcoat is offline
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Default Tranny Problems, Need Help

I have a 2006 Dodge Ram 1500 5.7l and it has gone into intermittent "limp" mode. It doesn't do it all the time, only now and then. I got into yesterday and drove 20 miles before it happened. I stopped at the store and when I came back out it was fine, then started back about 10 minutes later.

I took it to Advanced Auto Parts and they put the scanner on it. It was giveing the generic tranny problem code (P0700) as well as:
- P0750 (LR Solenoid) and
- P0882 (Low TCM voltage)

Several questions here,
- Has anyone experienced these two codes together? Could one be causing the other?
- Where is the TCM located? I have located the ECM, (Silver box with 4 connections on it, mounted to the firewall). Are the ECM and TCM integral or separate componenets? Does anyone have a picture of where the TCM is located if it is separate from ECM?

I love to tinker and have started tearing things apart but I need a little bit of direction. I don't want to mess anything up. A mechanic that I know said that more than likely if I replace the LR Solenoid it would fix the other code. Is this right?

Other things of note:
- I have in the last 6 months installed 2 amps in my truck, one for 6x9' and one for subs. Total RMS is about 900 watts. Could this be causing electrical issues with my TCM. Both are grounded to the chassis under the seat.

OK I know this is a lot of info to digest, any feedback would be greatly appreciated.

Last edited by leejeffcoat; 10-13-2012 at 03:07 PM. Reason: grammar
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  #2  
Old 10-13-2012, 06:47 PM
looka looka is offline
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Well, the TRS/Solenoid pack is known to go bad on these 545rfe trannys. To replace the solenoid pack you have to drop the pan, and remove the valve body which holds the solenoid.
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  #3  
Old 10-14-2012, 11:35 AM
leejeffcoat leejeffcoat is offline
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Would that have anything to do with the P0882 code? At first when I tested it, it was just throwing P0750, then I drove it down the road to another shop and started throwing the P0882 code.
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Old 10-14-2012, 01:04 PM
leejeffcoat leejeffcoat is offline
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I have deduced that the TCM is part of the ECM. Now I need to know which of the 4 connectors go to the solenoid pack. The connectors that I pulled out are the following colors from top to bottom:

Black
Orange
White
Green

Which one do I need to test? Which hole in the connector?
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  #5  
Old 10-14-2012, 04:21 PM
leejeffcoat leejeffcoat is offline
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I decided to go ahead and change the fluid what could it hurt.

See below picture as the difference between the old and new. You will be able to tell which is which.

http://i.imgur.com/7ZIHC.jpg
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Old 10-14-2012, 04:22 PM
leejeffcoat leejeffcoat is offline
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Maybe this plus new filters will solve the problem. Keeping my fingers crossed.
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Old 10-15-2012, 08:49 AM
TransEngineer TransEngineer is offline
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P0750 is an LR Solenoid Circuit fault. It is strictly an electrical fault (cannot be caused by old fluid, low fluid, failed gears or clutches, etc.). It can be caused by a bad solenoid coil (inside the trans solenoid pack), bad wiring (or a bad wiring connection), or a bad solenoid driver chip in the PCM.

P0882 is TCM input power low, which is also an electrical problem, and could, I believe, cause the P0750 to be set, so I would try to correct that first. P0882 indicates no (or too little) voltage from the Totally Integrated Power Module (TIPM) to the transmission solenoid pack (this same voltage is also fed back to the PCM, which monitors it at start-up and sets P0882 if the voltage is too low). Normally, this will also cause various trans Pressure Switch faults (such as P0876, P0871, P0846, etc.) to set. P0882 can be caused by bad wiring (or connections) or a bad TIPM.

You have a PCM (combined ECM and TCM) and the trans circuits are mostly on the C4 connector (with the green marking). First thing I'd recommend is to simply disconnect that C4 connector, and also the main harness at the trans, and check for any dirt / corrosion / bent pins / pins that are pushed back / etc. If OK just reconnect and see if all is OK. Often if you have a flaky connection on one pin, simply unplugging and reconnecting the harness will clean it up enough to fix the problem.

The main transmission electrical harness is on the driver's side of the trans. The 23-pin connector is on the solenoid / valve body and sticks vertically up out of the trans, a few inches above the oil pan rail.

The harness connector has a locking lever and a secondary latch. The transmission side of the connector is square and has two small round posts sticking out of opposite sides of the connector (one towards the front of the vehicle, one towards the rear). The locking lever on the harness (which is probably gray in color) wraps around three sides of the connector. The latch is on the driver's side. The two sides that wrap around have slots that engage with the two posts on the transmission connector. When the connector is unplugged, the locking lever (latch side) is down (toward the open end of the harness). When you plug it into the trans, the slots engage with the posts. Then, you push the locking lever latch bar up, which rotates the locking lever and clamps the harness connector down into the trans connector (by grabbing and pulling on those posts). I know this is hard to visualize... sorry but I don't have a picture.

To disconnect the harness, you first need to release the secondary lock. This is typically a red plastic piece (on the driver's side of the connector, just below the locking lever latch bar, which will be at the TOP of the connector when it's locked). You'll need to slide this red secondary lock either up or down (I'm not sure which, probably down but I'm not positive) before you can unlock the lever. Once that's done, reach up above and behind the center of the locking lever. The latch that holds the locking lever is just behind the face of the center of the locking lever (there's about 1/4 inch space between them). Put your finger behind the face of the locking lever, and push it and the latch APART. You need to push the latch (the piece just behind the top of the locking lever) in, towards the transmission (away from the locking lever) in order to release it. Once the locking lever pops free, rotate it down as you lift the harness up and off.

When you go to re-connect it, make sure the locking lever is DOWN (towards the open end of the harness connector) so it will engage the posts on the trans connector, then plug it in and rotate the locking lever up til it latches. Then slide the secondary lock into position to retain it.

Try this and see if it helps. If you still have the P0750 fault, post again here and I'll tell you how to diagnose it.
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  #8  
Old 10-15-2012, 10:33 PM
leejeffcoat leejeffcoat is offline
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Before I respond I just wanted to say thank you so much for the detailed response.

Now on to the nitty gritty. I did what you said and unplugged the connection at the PCM and at the Transmission. Both of the contact areas looked very clean, no signs of corrosion. In top of the connection that I pulled out the transmission (upper "female" black part, not the "male" white part coming out of the tranny) there was a bit of dirt and some bugs, but after close inspection all of the wires and connections to the connector looked good.

I plugged it back in and made sure it had a good connection. Started of down the road and "limp" mode kicked in after about 15 minutes on the interstate. I was running about 65 mph with the cruise control on going up a hill when it kicked on. Still P0750 code.

Now I guess its on to the next step of the diagnosis.

Thanks again for all the help.
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  #9  
Old 10-16-2012, 08:14 AM
TransEngineer TransEngineer is offline
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OK, so you've got an intermittent P0750 (LR Solenoid Circuit) fault. The PCM periodically (every 10 seconds, I think) checks the continuity of each of the main clutch solenoid coils. There are six of these solenoids (LR, UD, OD, 2C, 4C, and MS). To check each solenoid, the PCM briefly changes the state (turns it off if it was on, or on if it was off), and then turns it back to its original state. When each solenoid is on, it develops a magnetic field around the solenoid coil. When the current is turned off, this magnetic field collapses, which induces a short voltage spike on the solenoid wire. The PCM monitors the voltage on the solenoid wire, after it turns the solenoid off, and watches for this induced spike. If it fails to see the spike, it repeats the test. After I think 3 successive failures, it sets the related fault code (for the LR solenoid, P0750) and puts you into limp-in.

Now there are basically three different problems that can cause a solenoid circuit fault:
  • Solenoid coil is open (broken coil wire)
  • Wiring between solenoid and PCM is bad (open, or shorted into another wire)
  • Solenoid driver chip in PCM is bad (either not activating the solenoid properly, or not recognizing the voltage spike)
The problem is in tracking down which one of these is the real root cause. You can verify whether the wiring is the problem by doing a wire swap. If the fault will set while idling in Park, you can also use a wire swap to determine whether the solenoid or the PCM is bad.

You may need to have your dealer (or a shop) help you with this. They have a special tool for unlocking individual pins in the wiring connectors, allowing you to slide the pin (and wire) out the back side of the connector. You can pull out a couple of the pins, swap them, and reinstall the wires / pins into the "wrong" cavities in the connector. Here's what to do. I'll assume you have diagrams showing the pinouts (wiring locations) at each connector (if not, let me know):

1. Swap the wire that controls the LR solenoid with the one that controls the MS solenoid. Swap the wires at BOTH ENDS of the harness. So now the wire that used to carry the LR solenoid current is carrying the MS solenoid, and vice versa. Now drive the vehicle and see which fault sets. If you now get an MS Solenoid Circuit fault (P2706), then the problem must be the wire.

2. If you still get the original (LR) fault (P0750), then it's the solenoid, or the PCM. Now here's where it gets tricky. Can you get the fault to set if you merely start the engine and idle it in Park? If so, then swap the LR and MS wires again, but only at ONE END of the harness. Now the LR driver chip (in the PCM) is actually controlling the MS solenoid, and vice versa. So you CANNOT drive the vehicle like this - you will blow various faults and may actually damage the transmission! But you can start it and let it idle in Park (both LR and MS should be "on" electrically in Park). So start it up and let it idle. If you NOW get the same (original, P0750, LR) fault, then the problem MUST be the driver chip in the PCM (so you replace the PCM). If you now get the P2706 (MS) fault, then the problem must be the solenoid module (so you replace that).

If the fault won't set just idling in Park, then step 2 above won't work. In this case, you must gamble and replace either the PCM or the solenoid module. At this point, I would bet (based on experience) that the problem is likely in the PCM, so I would replace that first.

Hope this helps. Using this procedure often avoids "Well, we replaced the solenoid and that didn't fix it. So we replaced the harness, but that didn't fix it either. So now we're gonna try a PCM."
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