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Weird PCM Problem

38K views 19 replies 7 participants last post by  Burned 
#1 ·
Hi guys, I'm new to the message board and it looks awesome!
My truck pulled the dreaded "no bus" BS and its been doing it for quite some time now. I have had it off the road for a few months now and I really need to get it back running. It will get the no bus code and it wont start, I can get it to come back to life by unplugging and plugging back in the PCM. Sometimes it takes a few tries. I cleaned up all the grounds that I could find under the hood and so far no better. I replaced the battery, no better. Once I do get it to fire up, I notice that the lights seem to flicker a bit, interior and outside lights. The other problem is, when it does fire up it seems to be in "limp mode" this happened after unplugging and inspecting sensors. I tried to "reset" it by unplugging the negative battery cable but still in limp mode. Is there a sensor I should check? maybe I didn't plug it back in? I did have a buddy helping me for a bit and maybe one got missed. Thanks in advance guys! oh and the truck is a 2001 Dak sport auto 3.9L v6. I tried posting this in the troubleshooting forum too but figured there may be more pcm guru's in here.
 
#4 ·
Check the ground in the drivers kick panel under the dash! That can come loose and cause the No-Bus code. Also check the MAP sensor. This seems to be the main culprit for the limp-mode issues. If you have a multi-meter make sure you are getting 5V at the sensor by putting your test leads in the 2 outside pins of the 3-pin connector with the key "on" engine NOT running. Then, with the key "on" and the engine NOT running, connect one end you your meter to the battery negative and the other end to the middle pin and make sure it's close to 5V (Should be around 4.8V or so)
 
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#5 ·
Yo

trust me, check the crank sensor on the bell housing that connects to the distributor!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!:wave:
 
#9 ·
this is what the codes mean

P0713 (M) Trans Temp Sensor Voltage Too High Voltage greater than 3.76 volts (4-speed auto. Trans. Only).
P0753 (M) Transmission 3-4 Shift Soleniod/Transmission Relay Circuits An open or shorted circuit detected in the overdrive solenoid control circuit or trans relay circuit in JTEC RE transmissions . Was MIL code 45.
P1763 (M) Governor Pressure Sensor Volts Too High Voltage greater than 4.89 volts. (4-speed auto. Trans. Only)
P0113 (M) Intake Air Temp Sensor Voltage High Intake air (charge) temperature sensor input above the maximum acceptable voltage.
 
#10 ·
I would start with the P0753. Because it is the only one that doesn't say anything about the voltage being too high. It specifically says "Open" or "Shorted". SO maybe that sensor is bad and screwing with the rest?

Other than that I have no friggin clue man. Other than your PCM is shot.
 
#11 ·
thanks

Thanks a ton for the reply! Yeah that sounds like a good plan to me, do you know where that relay might be? I checked the obvious fuse box under the hood and just pulled the transmission relay and switched it with the one for the fog lights (same relay) and the lights still worked. The truck is in limp-mode now, but runs great for some odd reason. So would there be a relay on the tranny? Something may be unplugged too, thats my next mission. I have a feeling though that I will be in the wanted section of the forum looking for a pcm:rant:
 
#12 ·
Okay so after looking at an FSM for awhile and a little bit of research i believe that it can be a few different problems. The main ones pointed out in the FSM were

1. Bad governor pressure solenoid
2. Bad governor pressure sensor
3. Or bad PCM/TCM

Which of the things listed below would you say best describes the symptoms that are occuring with your tranny, from there i can give you a list of the possible culprits:



1. SHIFTS DELAYED OR
ERRATIC (SHIFTS ALSO
HARSH AT TIMES)
.

2. NO REVERSE (D RANGES
OK)


3. HAS FIRST/REVERSE
ONLY (NO 1-2 OR 2-3
UPSHIFT)


4. MOVES IN 2ND OR 3RD
GEAR, ABRUPTLY
DOWNSHIFTS TO LOW


5. NO LOW GEAR (MOVES
IN 2ND OR 3RD GEAR
ONLY)


6. NO KICKDOWN OR
NORMAL DOWNSHIFT
STUCK IN LOW GEAR
(WILL NOT UPSHIFT)

7. Or is the tranny just
stuck in limp mode (3rd gear)
and it won't come out.



Basically from all of the reading that Im doing i believe that like I stated before there is either a problem with one or more of the three things that I listed above. Or there is a problem with the eletrical signals going through the wires from the PCM to the tranny sensors. So to start off do a thorough check of all of the wires and connectors and make sure they are all clean and all of the wires and pins are intact. After that you would have to dive deeper into the testing of each of these individual components, we need to make sure that each of the sensors and solenoids are working properly and are clean. And if they are working properly we need to find out if the PCM is sending the signal out to the sensors and the signal is getting to these sensors from the PCM. If we can't figure out anything from there it might be time to bring it to the dealer and see what they have to say, you might even want to do that anyways and see what they have to say and what they think is wrong. From looking at this FSM it looks like there is a way to check all of these various sensors without tearing apart the tranny. There are various ports around the outside of the tranny were you can check the pressue to see if they are working right. But they require more than just your basic tools, probably something the dealer would have and could run tests with.



here are a few of the sensors that are in the tranny, the governor pressure solenoid and the governor pressure sensor are the ones that could cause this, along with a bad PCM.

http://www.transmissionpartsusa.com/A500_42RE_42RH_transmission_solenoid_s/10538.htm

Since you are having so many problems at the same time it kinda makes me lean towards the bad PCM, but they could be compound problems were one is causing all of the others, just like Boomin said. Hopefully we can get this figured out and prevent you from getting raped by the dealer, because they will charge you 300+ just to change the solenoid or sensor.
 
#13 ·
wow thanks a ton! The other day the thing went into no bus mode and basically told me to crap in my had and would not start. I knew that I could fire the thing up if I unplug the pcm and plug it back in but this time it would only fire up for a minute and shut back off. While messing with the plugs, I found the ground wires that come off of the harness that plugs into the pcm closest to the cab. The grounds were completely loose! Once I made sure they were tight, the truck fired right up and I have probably put 200 miles on it since and never got a no bus code again. I assume that ground is pretty important. As far as the transmission goes, when I put it in drive, it will start out in 3rd gear and stay there, no downshift or overdrive. I can shift the thing manually (1st, 2nd, 3rd, no overdrive) I can downshift it into second but not first. In order for me to get into first gear again, I have to go to N first or right from P. If I go from D. to 1rst, it will still start in second. Reverse works fine. Its weird because this was never going on while we were trying to diagnose the "no bus" issue, everything in the transmission still worked fine. I have no idea if anything is related but, just yesterday I needed to defog my windows and all of a sudden my blower motor isn't working and it was working a couple days ago. Thanks again for working with me so much on this one! I cant wait to get the thing up and running right!
 
#15 ·
Okay so know i would reset the computer and drive it until the code comes back up and pull it and see what it is know. I've got a feeling that it is a problem with the governor pressure solenoid now. Also before you do that go underneath the truck and check the plug that goes into the tranny and see if it is all good and clean and connected. I'm pretty sure you tranny is in limp mode and something is causing it to be like that and those solenoids are pretty big part int he shifting of the truck, they tell it when it is okay to shift. And if they aren't working it won't shift.

Sprinkle holy water on it and then BURN IT!! It's possessed!!

lol J/K Hope you get it all figured out.

Good idea get some of that stuff and give it to Bondslayer too.
 
#14 ·
Sprinkle holy water on it and then BURN IT!! It's possessed!!

lol J/K Hope you get it all figured out.
 
#16 ·
haha I'll work on getting that holy water. Pardon my stupidity but, where would I find this plug that plugs into the tranny? is it the one that plugs into what looks like a little black box? I tried to reset it by unhooking the negative cable and holding the key in start for 15 seconds but the CE light stayed on the entire time with the same codes. maybe I'll go down to an autozone or something and have them clear it with a scanner.
 
#17 ·
CONDITION POSSIBLE CAUSES CORRECTION
NO LOW GEAR (MOVES
IN 2ND OR 3RD GEAR
ONLY)



1. Governor Circuit Electrical Fault.



1. Test with DRB® scan tool and repair as
required.


2. Valve Body Malfunction.

2. Remove, clean and inspect. Look for
sticking 1-2 shift valve, 2-3 shift valve,
governor plug or broken springs.


3. Front Servo Piston Cocked in
Bore.


3. Inspect servo and repair as required.


4. Front Band Linkage Malfunction

4. Inspect linkage and look for bind in
linkage.


My guess again would be that it is # 1 and it has to do with the governor pressure solenoid. Mainly because you are throwing a code that has to do more electrically with the tranny and all the other possible causes to your problem are more mechanical and i don't know if they would throw a code. So again check all of the connections and then if it is still there then i would recommend looking into replacing the governor pressure solenoid and maybe even the governor pressure sensor while you are in there. Good luck to ya and get back to me after you check all of the stuff and see if the same codes are still showing up.
 
#18 ·
I don't know about on your truck but Iknow on my truck there is a plug that is located externally on the transmission. And IDK if you have a seperate PCM and TCM (I don't think you do) but if you do make sure all of the wiring is okay going between them. I just want to make sure once again that there isn't a problem with the wiring before you start changing parts. IDK exactly what to look for woth a voltmeter or something but maybe someone else can chime in on that part. But if the signal isn't getting from the computer to the tranny or vis versa that is probably your problem other than that it could be the actual sensors or a relay(someone mentioned something about that earlier).
 
#19 ·
My 05 Durango 4.7 was in limp mode shop informed me it was the shift solenoid, replaced it and it was good for a couple months and then started having having another problem, when I shifted to park the dash indicator said it was in reverse and the engine would not crank or start without letting it set sometimes over an hour and also would shut off while driving. I replaced the solenoid again and it was fine for a couple of months until one day I started up and it ran for about fifteen seconds and shut off tried to re start and nothing no crank no start went to Dodge dealer and bought brand new solenoid put on and still nothing no crank no start, check engine light is on but can't get it in to get codes and nothing comes up on the odometer when I try the key on off trick checked all fuses and grounds but now i'm thinking it could be the pcm tcm
 
#20 ·
If I had a no start issue I would be looking at the motor not the tranny. Is there any spark? Check the crank, and cam sensor. What is the fuel pressure?
Get it running and then worry about the transmission after.
 
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