08 Commander 4.7 (187,000 miles)need tranny help - Page 2 - JeepForum.com
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post #16 of 57 Old 11-11-2019, 08:41 PM Thread Starter
artisticchic24
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He came over with the good scanner. It came up each time that it could not communicate with the transmission. He then checked all the fuses. He is not good with trannys and keeps. Any ideas at all?!?🙏


What’s kind of scanner is he using? Kind of hard to diagnose when there’s no code. You can try unplugging the three connectors on the pcm making sure the connection is good. Check for obvious corrosion (white flakes) and reconnect it.
Any chance you could tell me where the PCM is located ?🙏

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post #17 of 57 Old 11-12-2019, 07:19 AM
Walt
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Any chance you could tell me where the PCM is located ?🙏
1. On my WK HEMI, it is located on the fender well, rear passenger side. Looks like a 5" x 5" x 1" flat box with electrical connectors coming into the bottom. Google "2008 WK PCM" to see a pic. On the HEMI, the TCM is built into the PCM. I assume yours is also.

2. If there is a communication problem, I would still expect to read a DTC (like P0700) alerting you to that (.....but maybe not if it is a part of the PCM). Recommend you re-check.

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post #18 of 57 Old 11-12-2019, 08:11 AM
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Another thing you can do with the bidirectional scanner is to do a transmission relearn. Many times it will fix electrical glitches with the transmission.
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post #19 of 57 Old 11-12-2019, 08:52 AM Thread Starter
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Trying both these tonight... thank you very much for the help!!
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post #20 of 57 Old 11-12-2019, 09:12 AM Thread Starter
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Just talked to my brother, he has a buddy that works with Jeeps and he’s been talking to him... they both are at a loss as to what’s going on. He said my tranny doesn’t have the smart whatever to do a relearn the transmission with the scanner.
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post #21 of 57 Old 11-12-2019, 09:16 AM Thread Starter
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It’s a Limited... if that matters
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post #22 of 57 Old 11-12-2019, 10:10 AM
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Are you sure he knows what he's talking about? I mean, I hate to question anyone who is a mechanic, but with a DRBIII the 545RFE can be run through a "quicklearn" which will wipe the TCM memory and recalibrate to factory settings. Maybe he doesn't have the ability to do it with his scan tool? You can run the TCM through quicklearn over and over again and in my experience each time will net slightly different results even though it's supposed to be a reset.
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post #23 of 57 Old 11-12-2019, 12:42 PM Thread Starter
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Just screenshot and sent what you wrote. I hope he is wrong lol
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post #24 of 57 Old 11-12-2019, 12:50 PM
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anything you can add-
other issues - dash lights, airbag, cruise control ?

Modifications- AUDIO system, lighting, performance additions?

Do you tow ?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #25 of 57 Old 11-12-2019, 02:46 PM Thread Starter
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anything you can add-
other issues - dash lights, airbag, cruise control ?

Modifications- AUDIO system, lighting, performance additions?

Do you tow ?
There aren’t any other issues... no warning lights( all are working in the dash) nothing new done to it since I’ve owned it a year. No modifications. Was shifting fine until it threw itself in 1st, no nosies that I can hear. It was towed after it happened, I was on side of the interstate 62 miles from home. Just goes into 1st and slap shifter isn’t working. I don’t use cruise control so I’m unsure if it works. I wish I had more but that’s it
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post #26 of 57 Old 11-12-2019, 03:16 PM
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Thinking out loud-
how sure are you it's in 1st gear - default is not 1st fear - place to look for codes is FDCM as well as the PCM/TCM.

Vehicle will start, you are claiming it does NOT shift out of 1st?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #27 of 57 Old 11-12-2019, 04:42 PM Thread Starter
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I know it’s first gear by the RPM’s when it goes from d to 1st. First time I was driving on interstate for a hour, no warning signs and it goes into first.,Towed home. Next time I drove it around my block for a hour before it went in 1st. Then last time I drove it for 8 minutes before it went into 1st. It goes back into drive after I take key out and restart it but randomly goes into 1st. Was thinking it was only doing it when it was warm but last time it was cold when it happened. I know limp mode is 3rd gear. I’m afraid to drive it out of my neighborhood so it’s sitting. Can’t afford to just throw parts at it. But not sure what to do. My brother is going to come back over with the scanner and see if he can relearn the transmission. Thoughts?
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post #28 of 57 Old 11-12-2019, 05:28 PM
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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.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #29 of 57 Old 11-12-2019, 07:00 PM
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This is the 545rfe. The NAG only came behind the 3.7l, 6.1L and 3.0l Diesel.

My issue I am getting stuck on is that if this was dropping down into first driving down the freeway. You would have a blown engine. It is a fluid coupling that will allow some slip but not that much. This is like a parts grenaded on the ground type of event if it drops into first at freeway speed.

There is no "TCM" with the RFE, it is all a function of the PCM. Though it still separates trans codes from the federally required PCM data and DTC's.

The Quick Relearn forces the computer to relearn the Clutch Volume Indexes (CVI's), basically how much ATF it takes to fill up/apply the clutch pack. It also resets learned shift strategies. This can be great to get it to stop doing funky shifts occasionally but wont have anything to do with the transmission dropping into limp home mode or worse, first gear.

If the scantool that is being used cannot see CVI's and cannot do the quick learn, I would not assume it is telling you all of the information you need. Part of the beauty of the computer controlled transmission is that it gets to decide if it wants to do what you are asking it to or not. If you tried to downshift to 1st on the freeway, you are simply an input to the computer that gets to say, "no way dummy." Now with a DTC(s) it will be more likely to do what you tell it so attempt at your own risk. There has got to be more information waiting to be retrieved in that computer. I cannot see how there would not be.

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post #30 of 57 Old 11-12-2019, 07:17 PM Thread Starter
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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.
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