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Discussion Starter #1
All,

I have a laundry list of "P" codes after a recent service but this one concerns me the most.

My local service center says that the Transmission Selenoid Assembly needs to be replaced.

I found P1790 as = Transmission Control Module Checksum

I'm also dealing with a P0731 fault code = Incorrect 1st gear ratio.

Questions....

1.) Is the Trans Control Module worth buyin on my own on line to save a few bucks?

2.) If yes...does this one look right ?

http://www.summitracing.com/parts/SMP-TCS51/

3.) Are the other/better tranmission modules that folks would recommend? I was quoted $785 for parts and labor on this one so looking to save some money if possible.

Thx,
Dave
 

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First you have a 2005, so you don't have a separate TCM. If it's just the solenoid, it's definitely worth doing it yourself over the dealer.
 

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You need to diagnose it more, before you just start throwing parts at it.

P1790 is not a "checksum" error. It is Fault Immediately After a Shift, which means your P0731 (Gear Ratio Error in 1st) happened within a few seconds after a shift (into 1st gear).

So the real problem is the P0731, which indicates slippage in 1st gear. Does the truck drive OK now, or does this fault keep resetting? Do you notice any trans slippage?

There are a number of issues that can give you a P0731 fault. Most are internal (i.e. you have to pull the trans and tear it down to fix them). I would recommend some further diagnostics, to find the real problem.

Give me some more details on how your trans is behaving now, and we'll work through it.
 

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Discussion Starter #4
You need to diagnose it more, before you just start throwing parts at it.

P1790 is not a "checksum" error. It is Fault Immediately After a Shift, which means your P0731 (Gear Ratio Error in 1st) happened within a few seconds after a shift (into 1st gear).

So the real problem is the P0731, which indicates slippage in 1st gear. Does the truck drive OK now, or does this fault keep resetting? Do you notice any trans slippage?

There are a number of issues that can give you a P0731 fault. Most are internal (i.e. you have to pull the trans and tear it down to fix them). I would recommend some further diagnostics, to find the real problem.

Give me some more details on how your trans is behaving now, and we'll work through it.

TransEngineer,

Thanks for your reply and willingness to help out. Here's what I can say.....

Yes..the truck is driving well right now. The check Eng light is on and off every other day. The few small things I have noticed are as follows;

1.) An occasional quick drop in RPM immediatly upon start...like on it's way to stall but then vrooom back to normal...this has only happened a few times.

2.) After I pull out of my parking lot and hit the first stop sign on my street I've noticed this same decrease in RMP and then it's back.

Truck seems fine to me other than that. Now I just had new plug and ignition cables installed last month...not that this means anything.

I haven't really felt any other slips in first gear..other than these few little stutters upon start and like at the first stop of the day.

Does this help get the conversation started?

Dave
 

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sounds like the tq vertor locking an unlocking...I know it's the most obvious..fluid level ok?
 

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Hmmmm....

The stumbles you notice could be the Torque Converter Clutch (TCC) dragging (it should be released when you come to a stop), and trying to stall the engine. But they could also be due to an engine performance problem (where the engine is stumbling all by itself, with no "help" from the trans). And neither one would explain the P0731 fault.

Do you get the stumble (at the first stop sign) every morning? If so, then tomorrow, try shifting the trans to Neutral as you're slowing down. That should at least indicate whether the stumble is caused by the trans, or the engine.

Check the faults again, and see if you have any engine-related faults. Also, has the P0731 reset? Does your trans ever go into limp-in mode (either stuck in 4th gear all the time, or launches from a stop in 1st but then shifts directly to 4th and stays there)? Do you ever notice slippage / flare in the trans?
 

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^^per his advice, a good test is shifting it to neutral coming to a stop..I had this same type of issue awhile back and i did remember habitually shift to neutral when I was slowing to a stop... at the time it did turn out to be my stall tq verter...
 

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Discussion Starter #9
Hmmmm....

The stumbles you notice could be the Torque Converter Clutch (TCC) dragging (it should be released when you come to a stop), and trying to stall the engine. But they could also be due to an engine performance problem (where the engine is stumbling all by itself, with no "help" from the trans). And neither one would explain the P0731 fault.

Do you get the stumble (at the first stop sign) every morning? If so, then tomorrow, try shifting the trans to Neutral as you're slowing down. That should at least indicate whether the stumble is caused by the trans, or the engine.

Check the faults again, and see if you have any engine-related faults. Also, has the P0731 reset? Does your trans ever go into limp-in mode (either stuck in 4th gear all the time, or launches from a stop in 1st but then shifts directly to 4th and stays there)? Do you ever notice slippage / flare in the trans?

Truck drove well this am..no hesitation on start..no stumble at the stop sign. This is not happening everyday....at least not yet. The check engine light was on & off again today so I am sure some faults hit. I have one for O2 sensors P0138, and for a bad brake switch P0571.

I do have fault code that I could not find that I should probably mention here..it's P0876. No idea what this one is.

I can also specifically say, for sure, that I did experience the "I'm stuck in 4th gear on the highway" issue...I was like wtf ?? There I was doing 65 mph and waiting for the shift..and nothing. I can only recall this happening once though in the last few weeks.

The check engine light is constantly going On & OFF almost daily so something is firing. Is there a place I can get fault codes checked besides the dealer and their $99 charge?
 

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Discussion Starter #10

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P0876 is a UD Pressure Switch Rationality fault, which means the UD pressure switch was in the wrong state (closed when it should be open, or open when it should be closed). This sheds new light on your problem....

Normally, pressure switch faults are caused by a wiring problem (loose connection, broken wire, etc.), since a broken or loose wire looks like a closed pressure switch to the PCM. Given your symptoms, however, and especially the P0731 fault, I'm thinking you're getting momentary loss of line pressure (causing an open UD pressure switch, and slippage in 1st gear, which sets the P0731). By the way, the P0876 fault will cause full limp-in (4th gear only).

Have you changed the fluid and filters lately? A misinstalled main sump filter (or seal), or an aftermarket spin-on (cooler return) filter, can cause problems with line pressure. Is your fluid level correct?
 

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Discussion Starter #12
P0876 is a UD Pressure Switch Rationality fault, which means the UD pressure switch was in the wrong state (closed when it should be open, or open when it should be closed). This sheds new light on your problem....

Normally, pressure switch faults are caused by a wiring problem (loose connection, broken wire, etc.), since a broken or loose wire looks like a closed pressure switch to the PCM. Given your symptoms, however, and especially the P0731 fault, I'm thinking you're getting momentary loss of line pressure (causing an open UD pressure switch, and slippage in 1st gear, which sets the P0731). By the way, the P0876 fault will cause full limp-in (4th gear only).

Have you changed the fluid and filters lately? A misinstalled main sump filter (or seal), or an aftermarket spin-on (cooler return) filter, can cause problems with line pressure. Is your fluid level correct?
Yikes..ok.

Fluids recently changed are Oil and Power steering ONLY. Just a had a full Power steering service. Plans to do coolant and 4x4 fluids as well as they are both dirty.

I recently replaced both of the below items myself...

Air Filter -> K&N permanent
PCV -> I had some oil drips on the old air filter and purchased and replaced the PCV valve myself as this was pretty straighforward. Could I have misinstalled the PCV? It just a simple align drop and turn 30 or degrees. Does this play any role in the lien pressure?

Sorry...when you ask what fluid level is correct..which are you referring to? I assume transmission but catch visualize where this is housed under the hood.

Took truck out this am...no check engine light..no stumbles.

Are there some basic wiring checks I can do to check for this loss of pressure issue. I'm a total rookie under the hood..but very willing to listen, learn, and my own research to id things.
 

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Yes, I'm sure he is referring to the trans fluid. I'm trying to remember....seems like the dipstick is on the passenger side near the firewall. This is from my 2004 owner's manual but the process is the same.

Fluid Level Check – 45RFE/545RFE​
Check the fluid level while the transmission is at normal
operating temperature 82°C (180°F). This occurs after at
least 15 miles (25 km) of driving. At normal operating
temperature the fluid cannot be held comfortably between​
the fingertips.

To check the automatic transmission fluid level properly,
the following procedure must be used:
1. Operate the engine at idle speed and normal operating
temperature.
2. The vehicle must be on level ground.
3. Fully apply the parking brake and press the brake
pedal.
4. Place the gear selector momentarily in each gear
position ending with the lever in P (Park).
5. Remove the dipstick, wipe it clean and reinsert it until
seated.
6. Remove the dipstick again and note the fluid level on
both sides. The fluid level should be between the “HOT”
(upper) reference holes on the dipstick at normal operating
temperature. Verify that solid coating of oil is seen on
both sides of the dipstick. If the fluid is low, add as
required into the dipstick tube.​
Do not overfill. After
adding any quantity of oil through the oil fill tube, wait
a minimum of two (2) minutes for the oil to fully drain
into the transmission before rechecking the fluid level.

NOTE:​
If it is necessary to check the transmission below

the operating temperature, the fluid level should be
between the two “COLD” (lower) holes on the dipstick
with the fluid at approximately 70°F (21°C) (room temperature).
If the fluid level is correctly established at
room temperature, it should be between the “HOT”
(upper) reference holes when the transmission reaches
180°F (82°C). Remember it is best to check the level at the
normal operating temperature.​
 

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Yikes..ok.

Fluids recently changed are Oil and Power steering ONLY. Just a had a full Power steering service. Plans to do coolant and 4x4 fluids as well as they are both dirty.

I recently replaced both of the below items myself...

Air Filter -> K&N permanent
PCV -> I had some oil drips on the old air filter and purchased and replaced the PCV valve myself as this was pretty straighforward. Could I have misinstalled the PCV? It just a simple align drop and turn 30 or degrees. Does this play any role in the lien pressure?

Sorry...when you ask what fluid level is correct..which are you referring to? I assume transmission but catch visualize where this is housed under the hood.

Took truck out this am...no check engine light..no stumbles.

Are there some basic wiring checks I can do to check for this loss of pressure issue. I'm a total rookie under the hood..but very willing to listen, learn, and my own research to id things.
The experience I had with the same fault codes were when I did not use the OEM trans filters. It took a while for the codes to show up, but my trans began to act a bit "odd" and I was told at the dealer to only use factory filters (both the sump and spin on should be replaced with Mopar only). I did not believe the dealer (who does), but I figured it was a cheap fix to try, and it truly worked. No more cheap filters for me on my trans after that. Also, using the Sonnax trans line booster caused me other issues as of late, removing that solved all that as well. Our transmissions are very picky to say the least!

On a side note, you have your stock radio/amp for sale in the classifieds, but I cannot reply to that post for some reason. I will take those off your hands, shoot me a PM to work out payment details if you still have it. I assume PayPal is good, will give you my PayPal info if you want to send me a payment request. Just let me know....and good luck with the trans!
 

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Went with Taylor ThunderVolt 8.2mm Spark Plug Wire Set and NGK Plugs.
good choice for plug wires (I have them too)..which particular NGK plugs did you go with (I run their copper 4306's)
 

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like transengineer said...fluid level and line pressure are important and can go hand in hand (sump filter too)... start truck, parking brake on and put it in neutral. then pull dipstick for trans fluid (passenger side next to firewall) and tell us where the fluid sits...and smell it too and let us know if it still smells sweet or burnt..
 

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Discussion Starter #17
good choice for plug wires (I have them too)..which particular NGK plugs did you go with (I run their copper 4306's)
same as you!!!!:smileup:
 

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Discussion Starter #18
good choice for plug wires (I have them too)..which particular NGK plugs did you go with (I run their copper 4306's)
like transengineer said...fluid level and line pressure are important and can go hand in hand (sump filter too)... start truck, parking brake on and put it in neutral. then pull dipstick for trans fluid (passenger side next to firewall) and tell us where the fluid sits...and smell it too and let us know if it still smells sweet or burnt..
Will do and thank you!
 

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Discussion Starter #19
An additional finding to note here..bear with me on this explanation....

So I always back into my parking spot in the lot I park in. I have noticed on occasion that when I started truck, place it in DRIVE, and release the brake that i don't get movement (i.e no fwd roll), with the truck in DRIVE....without having to step on gas. It's almost as thought my parking brake was ON but in all cases it is not. Could the Parking brake be sticking here? Could this also be related to the current issues we are trying to diagnose here with the trans and line pressure?

Like I said..it doesn't happen all the time. When it does not happen the truck easily rolls forward when in drive, foot OFF brake, but NOT on gas pedal.

I hope this makes sense and others can comment on this.

Dave
 

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An additional finding to note here..bear with me on this explanation....

So I always back into my parking spot in the lot I park in. I have noticed on occasion that when I started truck, place it in DRIVE, and release the brake that i don't get movement (i.e no fwd roll), with the truck in DRIVE....without having to step on gas. It's almost as thought my parking brake was ON but in all cases it is not. Could the Parking brake be sticking here? Could this also be related to the current issues we are trying to diagnose here with the trans and line pressure?

Like I said..it doesn't happen all the time. When it does not happen the truck easily rolls forward when in drive, foot OFF brake, but NOT on gas pedal.

I hope this makes sense and others can comment on this.

Dave
Does it depend at all on how long it was since the truck was last driven? You might be getting converter drainback (some of the oil in the converter draining back into the trans sump). If you step into the gas (when it doesn't move by itself) does it go right away, or does it kind of "ooze" slowly into gear? Also, try just leaving it in Drive (foot off the brake) for a longer time (maybe 30 seconds). Does it just sit there forever (never moves until you give it the gas), or does it eventually start to move normally?
 
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