08 Commander 4.7 (187,000 miles)need tranny help - Page 3 - JeepForum.com
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post #31 of 57 Old 11-12-2019, 07:29 PM Thread Starter
artisticchic24
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Originally Posted by jtec View Post
I am thinking this is a NAG 1 let me know...
the 1st gear is a head scratchier.
Am I to understand you were at hiway speed cruising at 65+ and it downshifted to 1st? that does not sound likely SO details.

First is a commanded gear and solenoids must be configured ON where as default to 3rd is all solenoids unpowered inop open, a lack of control or command.

Any deep water, rain, a hail mary look at wiring at trans pass thru. the connector

I like a challenge and this is a new one - keep me in loop please.

good news is your daughter got into perdue.
No water or anything. It was chilly but other than that normal driving conditions. I will keep everyone in the loop. I appreciate all the help and suggestions!

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post #32 of 57 Old 11-12-2019, 08:08 PM
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When it first happened, I was going about 75. No warnings it just happened... rpms went over 5000. I immediately pulled over. It freaked me out when it happened. I’m going to have my brother read what you have wrote. The second and third time, I wasn’t going fast because I was expecting it to happen. I couldn’t go over 10 without reviving the rpms up.
75 mph and 5k rpms is not first gear. It is probably closer to 3rd gear like is expected for limp home mode. Limp home mode is a mechanical gear set that the transmission defaults to if there is an error to protect the transmission.

If it went into 1st the wheels would overdrive the engine through the transmission and you would have likely revved over 10k rpms blowing the gerbils into lower earth orbit.

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post #33 of 57 Old 11-13-2019, 07:09 AM
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Due to NO football last night and being bored to tears, I did some reading my colleague 2005JGC was correct this is a 545RFE trans.

It is in limp mode 2nd gear most likely. A "Manual valve" permits limp mode, you should also have R and duh P.
The TCM is incorporated to the PCM (academic) and the codes SHOULD be accessible very least being p0700.

WHY you are having issues getting the codes is 1st issue. Was the scanner communicating with the PCM?

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When I see the quality of aftermarket I think OEM.
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post #34 of 57 Old 11-13-2019, 08:18 AM
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FWIW , at 75 mph - 4500 rpm on stock tires and 3.73 gear ratio = ~1.41 transmission ratio which = 3rd gear. like 2005JGC stated, this is normal limp in mode. If your gear selector is saying you are in 1st, you automatically have a mismatch between the modules that talk to the gauges and the actual gear selection. which would cause this limp mode by itself. The question is which one is happening first to cause the other.

If you could pull a code I would think a U101 - no communication with TCM would come up. ( that may be what your bro was getting but the scanner was just spelling it out instead of a numerical DTC ). I have heard of this before on the forums and it generally resulted in a new PCM as the TCM is integral to the PCM with that transmission.

Just to be certain, after the drop to 1st gear, do you still have forward momentum without restarting the jeep? can you just drive away again or does the jeep rev out like it's in neutral?
You should be able to easily do 60mph at about 2500rpm in 3rd gear. Not that I would suggest going on the highway, but you should be able to drive around the area fairly normally.

If you want somewhere physical to look at, I think it was already suggested to have your bro pull the PCM connectors and have a good look at the pins on both sides ( corrosion or loose ) maybe give them a dab of dielectric grease. While you are doing that I would pull the positive battery cable off the battery and ground it out to the frame. then when you reconnect the battery turn the ignition switch to on ( without starting it) and press the gas pedal down 3 time in 5 sec . This should clear all memory and reset the PCM to near factory settings.

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post #35 of 57 Old 11-13-2019, 08:33 AM Thread Starter
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My bro is coming back over today with the scanner and to look at the PCM. You all are awesome and I greatly appreciate you all helping us out with this!
When it first happened it was totally unexpected and at I was like what is going on. When I looked ya my dash and letting off the gas pedal it was at 5000 rpm, it could have been higher. Instant panic! Lol
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post #36 of 57 Old 11-13-2019, 08:49 AM
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A no communication fault to a module or ECM is often due to lack of power feeds, ground connections or a communication bus problem. A wiring diagram is needed to see which wires or connector pins to check. A test light can check the power and grounds but a pricey scope is needed to check the bus communications. If all those tests are good it means you need a new ECM/module. There are some good youtube videos by Eric O at South Main Auto (and others) showing these tests being done. Hopefully you can find a local shop with the right equipment to diagnose it otherwise the dealer would be an option.

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post #37 of 57 Old 11-13-2019, 09:20 AM Thread Starter
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Originally Posted by yzjwk View Post
FWIW , at 75 mph - 4500 rpm on stock tires and 3.73 gear ratio = ~1.41 transmission ratio which = 3rd gear. like 2005JGC stated, this is normal limp in mode. If your gear selector is saying you are in 1st, you automatically have a mismatch between the modules that talk to the gauges and the actual gear selection. which would cause this limp mode by itself. The question is which one is happening first to cause the other.

If you could pull a code I would think a U101 - no communication with TCM would come up. ( that may be what your bro was getting but the scanner was just spelling it out instead of a numerical DTC ). I have heard of this before on the forums and it generally resulted in a new PCM as the TCM is integral to the PCM with that transmission.

Just to be certain, after the drop to 1st gear, do you still have forward momentum without restarting the jeep? can you just drive away again or does the jeep rev out like it's in neutral?
You should be able to easily do 60mph at about 2500rpm in 3rd gear. Not that I would suggest going on the highway, but you should be able to drive around the area fairly normally.

If you want somewhere physical to look at, I think it was already suggested to have your bro pull the PCM connectors and have a good look at the pins on both sides ( corrosion or loose ) maybe give them a dab of dielectric grease. While you are doing that I would pull the positive battery cable off the battery and ground it out to the frame. then when you reconnect the battery turn the ignition switch to on ( without starting it) and press the gas pedal down 3 time in 5 sec . This should clear all memory and reset the PCM to near factory settings.
I do have forward momentum after it goes into 1st, it goes into park and reverse as well.
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post #38 of 57 Old 11-13-2019, 09:21 AM Thread Starter
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The seconds and third time it happened in my neighborhood and I couldn’t go over 10 mph with reviving up the rpms
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post #39 of 57 Old 11-13-2019, 09:23 AM Thread Starter
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post #40 of 57 Old 11-13-2019, 11:28 AM
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The seconds and third time it happened in my neighborhood and I couldn’t go over 10 mph with reviving up the rpms
So once the speed gets within range, then it's stuck in first unless you turn the vehicle off and restart it ?
That would in turn probably reset everything to normal making normal diagnostics difficult.

Did you try getting DTCs or Live data on the scanner right after the issue and without turning the vehicle off ?

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post #41 of 57 Old 11-13-2019, 05:29 PM Thread Starter
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Originally Posted by artisticchic24 View Post
The seconds and third time it happened in my neighborhood and I couldn’t go over 10 mph with reviving up the rpms
So once the speed gets within range, then it's stuck in first unless you turn the vehicle off and restart it ?
That would in turn probably reset everything to normal making normal diagnostics difficult.

Did you try getting DTCs or Live data on the scanner right after the issue and without turning the vehicle off ?
He tried to scan it after but he had his cheaply scanner from home. It didn’t pull any codes.
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post #42 of 57 Old 11-13-2019, 05:36 PM Thread Starter
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Not sure if this has anything to do with everything else but my battery was dead this morning. I pull the Jeep into my driveway Monday so I could pull my daughters car in the garage. We got snow Monday. This morning I went to pull the Jeep into the garage because my brother was coming to scan it again and relearn the tranny. The battery was dead, the hood was closed but not completely... like when you pull the hood release lever. Now it has been really cold but no lights where left on or anything. I had him get me a new battery because for had no idea how old it was and it was a good idea to just change it. Think the dead battery has anything to do with anything that’s going on?
My brother did come over and did a bunch of things... he’s going to type it all out for me to post on here. But no luck with relearning it. He also checked for corrosion on the PCM connectors and there wasn’t any. He also took photos but I don’t see that I can post them in this thread.
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post #43 of 57 Old 11-13-2019, 05:41 PM Thread Starter
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I wish I could post pictures he sent me of the scanner screen. Anyway there was a option to test the electronic shifter... it gave a error- unable to complete task...on the shifter. Could the shifter cause this all to happen? I know it has. a circuit board down there
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post #44 of 57 Old 11-13-2019, 06:20 PM Thread Starter
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First off thank you guys for trying to help my sister with this issue, we really appreciate all your thoughts and input!
Also I am not a mechanic, I am a Bodyshop guy that does his on mechanical work, mostly suspension work so this is a little out of my wheel house!
So today I went back over, inspected the PCM terminals, all looked good and clean, replaced the battery, grounded the positive cable while it was disconnected,did the reset with the gas pedal. Drove it out of her neighborhood for less than 5 minutes before the display changed from D to 1. When this happened it automatically downshift into what I am pretty sure was 2nd gear. As I continued to slow down it downshifted into 1st. I continued driving and it would not shift out of 1st. Was doing 20mph at 3000rpm’s.
Made it back to the house, plugged the scanner in and selected read all DTC’s.
After the scan completed it only had some TPMS codes 0 engine and the transmission showed not scanned again. I found the area to reset the trans so I did that, I placed it in drive and it changed to 1st almost immediately. So then I reset the ECM but had the same results. I fumbled my way through several other tests but really wasn’t sure what any of the data was telling me. Nothing jumped out as odd though. All this being said, if any of you have more knowledge on what tests to run and what indicators to look for in the data I would greatly appreciate it! Thanks again for your time guys!
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post #45 of 57 Old 11-13-2019, 07:10 PM
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Originally Posted by artisticchic24 View Post
First off thank you guys for trying to help my sister with this issue, we really appreciate all your thoughts and input!
Also I am not a mechanic, I am a Bodyshop guy that does his on mechanical work, mostly suspension work so this is a little out of my wheel house!
So today I went back over, inspected the PCM terminals, all looked good and clean, replaced the battery, grounded the positive cable while it was disconnected,did the reset with the gas pedal. Drove it out of her neighborhood for less than 5 minutes before the display changed from D to 1. When this happened it automatically downshift into what I am pretty sure was 2nd gear. As I continued to slow down it downshifted into 1st. I continued driving and it would not shift out of 1st. Was doing 20mph at 3000rpm’s.
Made it back to the house, plugged the scanner in and selected read all DTC’s.
After the scan completed it only had some TPMS codes 0 engine and the transmission showed not scanned again. I found the area to reset the trans so I did that, I placed it in drive and it changed to 1st almost immediately. So then I reset the ECM but had the same results. I fumbled my way through several other tests but really wasn’t sure what any of the data was telling me. Nothing jumped out as odd though. All this being said, if any of you have more knowledge on what tests to run and what indicators to look for in the data I would greatly appreciate it! Thanks again for your time guys!
Sounds like the CAN bus is communicating if all the other modules are showing, so that’s good.
If you turn the jeep off and back to on without starting, or reset with the battery disconnect to where it is initially driveable , can you then read the TCM with the scanner?

Another thing to check although I don’t think it’s related is the 20 pin connector coming off the transmission and the transmission control relay in the power distribution center under the hood.

I think the TCM is loosing power during the drive but according to the service manual, it should retain the one battery lost code...

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