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Pete
Pete, Automotive Mechanic
Category: Transmissions
Satisfied Customers: 24726
Experience:  GM and Mercedes vehicle technician.17 years experience.
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I have a 2005 Jeep Grand Cherokee with the 3.7L v6 and NAG1

Customer Question

I have a 2005 Jeep Grand Cherokee with the 3.7L v6 and NAG1 transmission. I bought the jeep from a neighbor. She had been told by the local Jeep deal that the transmission was in need of a rebuild after they replaced the TCM and the Transmission was still slipping in all gears. (It takes reving up to 2,500 to 3,500 rpm to get the vehicle to move. I rebuilt the transmission with the help of an ATSG manual. (I have successfully rebuilt a 47re and a 48re before so I felt I could handle the NAG1 with the manual) ANyhow, the trans would not do anything once rebuild was done. EXCEPT
JA: This is potentially serious. How long has it been going on?
Customer: the last year.
JA: Are you fixing your Grand Cherokee yourself? What have you tried so far?
Customer: Yes, I have rebuilt the transmission, swapped in a used valve body, swapped in a used TCM, and most recently swapped in a different NAG1 transmission (Came from a junk yard out of a jeep that was in a minor accident, so that transmission was working at the time of the accident)
JA: Anything else you want the mechanic to know before I connect you?
Customer: I took it to the local Dodge dealer to have the check it out and they said they got the TCM and PCM and shift module all talking together again, but that the transmission was the issue. )This is what led to the transmission from the junk yard out of the jeep that had been in the accident) It is still acting just like it did the day I bought it.
Submitted: 2 months ago.
Category: Transmissions
Customer: replied 2 months ago.
Which is to say it slips in any gear forward and reverse. There was one quirk, I have not been able to get manual shift mode to engage (When the "d" on the PNRD display switches to show your current gear.) There was one time after the transmission rebuild that I was able to get it to engage the manual shift mode and when that happened I did seem to have normal function in forward and reverse with the rebuilt transmission. It worked one time and never again since.
Expert:  Pete replied 2 months ago.

Hi my name is ***** ***** I will be happy to assist with this today.I apologize for any delay.

Have you had the fault codes re checked recently with a fully compatible scan tool to see what codes are setting with this issue here?

Let me know so we can continue,thanks Pete

Customer: replied 2 months ago.
When I had it in to the Dodge dealer they said all transmission codes were cleared out. (They did say there was an issue with one of the o2 sensors showing a fault to ground, but all trans codes were clear)
Expert:  Pete replied 2 months ago.

Was wiring ever checked leading from the computer to the transmission at all for any corrosion or damage?

Customer: replied 2 months ago.
I checked all the wires to the solenoids and speed sensors today and each wire is totally open to chassy ground as well as to sensor ground with both ends of the wiring harness disconnected. When connected I was able to read all the solenoids resistave load (4.2 to 5.2 ohms read at TCM connector C2 terminals) Also was able to read 5.62m ohm and 5.4m ohm to the speed sensor wires.
Expert:  Pete replied 2 months ago.

Is the engine revving up to 2500 or 3500 rpm before it moves at all?

Customer: replied 2 months ago.
Yeah, pretty much to get it to move, you have to rev it a lot. Funny thing is it has acted the exact same way with the original transmission as well as the one from the junk yard, had to rev it about the same no matter which one was in it.
Expert:  Pete replied 2 months ago.

O.k.,so we can rule out the transmission and wiring.

How many times was the TCM replaced?

Customer: replied 2 months ago.
Just twice.
Expert:  Pete replied 2 months ago.

Same results with both TCM's?

Customer: replied 2 months ago.
Actually had 3 TCM's - one from the factory, two replacements. All had same results.
Expert:  Pete replied 2 months ago.

Do you have a scan tool that displays throttle position sensor data signals?

Customer: replied 2 months ago.
No, I don't...
Expert:  Pete replied 2 months ago.

With all that has been done here this sounds like a possible fault with your throttle position sensor sending an incorrect signal which can cause the engine computer to send incorrect signals to the tcm.In some cases it can be the engine computer at fault needing replaced but if you can I would have the throttle position sensor checked for any issues with it needing replaced.Usually this is checked with data signals on a compatible scan tool.

Let me know if you need anything else and feel free to rate my help here as this is how I receive credit for my time.A 5 star rating is appreciated.Thanks Pete

Customer: replied 2 months ago.
Hi, Ok, I will check into the tps. Also, I was wondering about checking the 5v feed to the tcm. (My thought is it possible it could provide 5v but the supply circuit is no longer able to provide enough current to drive the solenoids properly so they close off the oil passages in the valve body properly? )
Expert:  Pete replied 2 months ago.

This is possible.It can provide enough voltage but if there is corrosion or damage to the wiring or connection this will cause low amperage that will cause this fault here.I would trace the transmission wiring from the transmission to the TCM and see if any corrosion or damage is found.

Thanks Pete

Customer: replied 2 months ago.
Ok will do. Also, where does the TCM get it 5v supply from? Does it regulate its own 5v from a 12v feed or does it get sent over from the PCM or?
Expert:  Pete replied 2 months ago.

Let me take a look real quick I will post back here shortly.

Expert:  Pete replied 2 months ago.

The TCM does make its own 5 volt from the 12 volts it receives.Shown as the sensor supply voltage.Below is the diagram info for the TCM on this model here.

https://www.dropbox.com/s/11nq4zaix5l8h8p/t-09-28.gif?dl=0

https://www.dropbox.com/s/io6qli7q3hmskrq/tr-09-28.gif?dl=0

https://www.dropbox.com/s/jjt0mgllllf39ns/tran-09-28.gif?dl=0

Customer: replied 2 months ago.
A couple more things. 1) There has been a stumble when hitting the gs hard, so I think you may very well be right about a bad TPS. 2) A bad TPS shouldn't keep the trans from going into manual mode, should it? What conditions have to be met in order for the transmission to go into manual mode? (I don't really care too much about manual mode, but the one time it went into manual mode, it seemed like the trans worked normally...)
Expert:  Pete replied 2 months ago.

Well in some cases if a TPS is sending erratic signals it can cause transmission shifting and operating issues,I have seen this several times before.I would double check the transmission wiring for any issues needing resolved as well here.Usually no codes set and no over heat issues and the throttle position sensor reading correctly will allow manual mode.

Thanks Pete

Customer: replied 2 months ago.
Hi Pete,
I found that my obdII tool did have a tps readout. The throttle showed 17% t idle and would only go to 70% when the gas pedal was all the way to the floor. I figured it was a bad tps sensor so I got one and installed it but it is still having the same issue, just now reading 16.5% throttle when the vehicle is idleing. So what are the wires/ connectors on the ECM that I need to check to be able to check the tps wires? ThanksGod bless...
Mark
Expert:  Pete replied 2 months ago.

If you open the throttle plate by hand with the scan tool connected does the tps show 100%?

Customer: replied 2 months ago.
Hi Pete. moving the throttle plate by hand gives a reading of 77% when the throttle plate is hitting the stop in the throttle body.
Customer: replied 2 months ago.
Is there some way to reset the throttle sensor to the ECM? (I know on my 2003 Dodge Cumins, you have to reset the ECM to the range of resistance of the APPS as they call it on the dodge, but it serves the same purpose as the tps on this jeep)
Expert:  Pete replied 2 months ago.

It does look like your TPS is sending a correct signal here.This is a difficult question for me to answer myself with all that has been done and I dont show any testing info for the TPS sensor or transmission controls for the transmission myself.If you didnt get a chance to reinspect the wiring I would check and see if any wiring issues are found.If you would like I can open your question for others here to see if anyone else can assist further on this just let me know if this is something you would like to do.

Thanks Pete

Customer: replied 2 months ago.
Hi Pete, I think that sounds good to me to open this up to others and see if someone else knows what to do with this.
Expert:  Pete replied 2 months ago.

I will open your question up for others here to see if someone else can assist further on this as there may be others here that may have more info on what to check or do with this issue.I hope you can get this resolved with ease.No need to reply to my last post here unless it is a last resort as it will keep your question locked to me and others will not be able to view it.If you feel you want to continue to work with me on this feel free to reply at any time but keep in mind in some cases it can be difficult to fully diagnose or help repair this without seeing your vehicle.

Thanks Pete

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