p0841 Troubles

[dmaxdallas]

Originally Posted by Mike L.

Ohm test will usually tell you if they are ok, but it doesn't gaurantee they will work ok. Switching the shift solenoids with each other is a better test. If one solenoid is bad, putting it in a different hole will change the code. Testing the PSM can be done with a DVOM hooked up and depressing the little switches with a pencil eraser. You will see the switches open and close. Having a Tech 2 really helps with these kind of tests.

Thanks for all the info mike! I have a tech 2 at my disposal here as well

[dmaxdallas]

Well I drained the fluid and pulled the pan last night but ended up running out of free time. Will be tearing into it after work today.

Few questions for you Mike:

What is the torque spec for the pressure switch manifold bolts?

Do you think I should go ahead and remove the valvebody from the truck?

Is there anyway this could be an e shift valve problem?

Before I drained the fluid I tried clearing the p0841 one more time to no avail, also put the truck into Drive to verify the trans is till stuck in 5th, which it definitely is. What would make the trans resort to sticking in 5th gear like that?

I have a multimeter, a tech 2, and a new internal harness, any other tools/equipment you’d suggest? I can borrow things from work if need be.

My plan is to check the A and B trim solenoids for 5-8 ohms of resistance, and the C shift solenoid for 20-30 ohms.

Along with this, verify that the pressure switches each ground when depressed.

I am definitely not a transmission guy here so just going by what I’ve been told, read, or had suggested by someone. Any other diagnostic tests that could help pinpoint exactly what is wrong with the trans?

[clrussell]

Dallas if you didn't get it figured out this evening let me know. I don't know anywhere near as much as mike on this. But I have service Info if it will help you any.


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[dmaxdallas]

I want to start off by saying a huge thanks to Mike L. for speaking on the phone with me last night, I am definitely not a trans guy so any amount of guidance helps greatly.

A little update of what I’ve managed to diagnose. Last night I checked all the solenoids for proper resistance across the pins. Everything appeared to be within spec so I swapped them around in their locations to see if the issue would follow a potentially problematic solenoid when it moved. Also replaced the pressure switch manifold and internal harness before putting the pan back on and filling it up.

To my utter disappointment, still have the p0841 and the trans is still stuck in 5th gear, with no reverse. Thinking at this point maybe a stuck valve?

Or are there electrical circuits deeper in the trans?

[dmaxdallas]

Originally Posted by clrussell

Dallas if you didn't get it figured out this evening let me know. I don't know anywhere near as much as mike on this. But I have service Info if it will help you any.


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Thanks, I'm pretty lost here honestly. Hoping its nothing too big

[dmaxdallas]

Bump it up

[clrussell]

Got swamped at work today. Been fighting a cummins no start. I'll try to see if I can find ya some more info than you already have


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[dmaxdallas]

Going to pull the valvebody completely out this weekend and check for stuck valves. Any possibility this could be an NSBU switch?

[dmaxdallas]

Well I removed the valve body from the truck this weekend and completely disassembled it to clean and make sure none of the valves were sticking. Cleaned everything up with brake-clean and reassembled making sure that each of the valves moved freely in its bore. Fresh fluid, filters, and what should be a properly functioning valve body still changed nothing. Still have the p0841 that won’t go away and still stuck in 5th gear with no reverse. Going to attempt getting ahold of a known good tcm to swap out with mine to eliminate the TCM as being the problem. Besides this, does anyone have anymore ideas? Starting to think something might be horribly wrong with the trans.

[dmaxdallas]

One last bump to see if anyone has any ideas or things to try.

Still trying to get ahold of a different tcm to test that being the issue

[dmaxdallas]

If I unplug the round connector at the passenger rear of the trans then I am able to force limp home. So, if disconnected from the tcm, the trans is capable of engaging both reverse and third gear. With everything hooked up correctly, I have no reverse and Drive is 5th gear only. Starting to think tcm might be the cause.

[dmaxdallas]

Finally got ahold of another TCM and swapped it in last night. Code is gone and trans appears to be acting normal again. Still chasing a couple accelerator pedal issues before I get some miles put on it. Thanks to everyone for the help they offered along the way!

[nsolimini]

Glad you found the issue. I was having similar issues about 8 months ago and I found out my torque wrench was junk. The valve body is about 9ft lbs of torque and my wrench was putting out about 17ft lbs.

Long story short too much torque on the valve body was making my valve get trapped.

[dmaxdallas]

Originally Posted by nsolimini

Glad you found the issue. I was having similar issues about 8 months ago and I found out my torque wrench was junk. The valve body is about 9ft lbs of torque and my wrench was putting out about 17ft lbs.

Long story short too much torque on the valve body was making my valve get trapped.

Yeah that'll get ya! I specifically took home a freshly calibrated Snap-On torque wrench from work for that very reason

[Jordanmt]

I have an 05 lly with an Allison 1000. Im having almost the exact symptoms as this. P0841, 5th gear limp, and no reverse. The one thing I would add I didn't see mentioned here is that the problem fluctuates with temperature. I can get in the truck in the morning, back out of the driveway put it in drive and go 3 miles to work. After 8 hours I drive home fine. If I drive any further than that and the truck gets up to normal operating temperatures it will limp in 5, usually when slowing down. The light comes back on. P0841. No reverse. Sometimes when it gets real warmed up it will give me range shift inhibited and won't take any gear. Like in the thread here, if I'm in a jam, I can unplug the top harness to the TCM and it will limp in 3rd and let me have reverse. Just recently however it decided to give me some more codes. All seem to be electronic related. P0768 shift solenoid 4 control circuit low voltage. P0763 shift solenoid valve 3 control circuit. P0748 pressure control solenoid valve control circuit. I'm a back yard mechanic at best. All I've done to problem solve was do a resistance test on each wire for the harness from the top of the TCM to the passenger side of the trans. And same thing on the internal harness. No resistance anywhere in the wire. I have not swapped any parts as I don't have the money to play the guessing game. I spent a lot of time online trying to find someone with a similar problem and this is the closest I've come. Does anyone think I may need a new TCM aswell? Is it worth it to get one used? Is it something wrong inside the trans? Someone please help!!!