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Ask Dean @ TransLab Your Own Question
Dean @ TransLab
Dean @ TransLab, Hotline Technician
Category: Dodge
Satisfied Customers: 129
Experience:  30+ years in automotive driveline
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96 dodge ram 2500 4x4 diesel problem with 3-4 shift. It shifts

Customer Question

96 dodge ram 2500 4x4 diesel problem with 3-4 shift. It shifts fine when I first start driving but after a few minutes the transmission will not shift into 4th gear. I have checked the codes and only get the coolant temp sensor voltage is high (5v. So I chnged the sensor under number 6 cylinder nera the firewall and reset the computer with the scan tool. I still get the error code and the truck will not shift into 4th gear. I checked the wire from the pcm connector and the sensor by placing a meter accross the connector and engine and get the same value as the sensor by itself so I think that part is OK. What else can I do to get the coolant sensor to work? Does this mean the PCM is bad?
Submitted: 7 years ago.
Category: Dodge
Expert:  Dean @ TransLab replied 7 years ago.
hi hawkshaw...

look near the thermostat housing and upper hose area and see if you find a sensor there.
it sounds like you replaced the oil pressure sender.

as for 4th gear, if you want to test to find out whether this is a trans problem, or control problem (since 4th is electronically activated), look on the trans next to the shifter lever. the torqueflite OD trans (47RH /hydralic or 47RE /electronic governor control system) will have either a 3 pin connector, or a 8 pin connector. Your's is a 3 wire. The center pin is hot, and the other 2 are grounds for lockup and 4th. If i remember correctly the front pin is ground for 4th gear. You can jumper with a scotchlock and wire to a toggle switch with remote ground. when you get up to speed and it doesn't shift to 4th, flip the switch to provide ground. If it goes right in 4th gear then we know the trans is ok but the controler is not shifting to 4th because of the temp code or some other unreported problem. but at least you have verified that trans 4th WILL WORK (wheew! trans ok).

while you're checking 4th i'll double check temp sensor location. i'm not at the shop right now. I'll also check the ecm pin numbers for it

Dean
Customer: replied 7 years ago.
I am sure the sensor I replaced is a temperature sensor although it may only be for the insturemnt panel guage. I cannot find any reference to a second temp sensor on a 96 cummins diesel accept for the california engines with EGR. But I will take your advice and see if there is a sensor in the thermostat area. I can make the transmission shift if I get the truck up to speed and take my foot off the throttle. I checked the voltage on the tps and it is right at 1v at idle position. I also checked the kick down cable for adjustment and looks right so I don't think that is the problem either. I really think the problem is this PCM coolant temp sensor issue. I went out and pulled the connectors off the PCM and measured the resistance through the wire and sensor which looks ok I could not determine which pin is ground for the sensor so that may the issue.I will try the toggle switch idea but I really think the tranny is ok, just some elctrical issue if I could just find it.
Expert:  Dean @ TransLab replied 7 years ago.
ok 1v at idle is about right, but what about at the speed when you expect 4th?

the cummins is notorious for vibration related TPS failure, when voltage drifts above what SHOULD be there, OR you will see the volts fluctuate while at steady throttle and speed.
Those babies are expensive, and come with the bracket, but are common cause of no 4th or even more commonly no lockup, or LOCKUP SHUTTLE SHIFTING. does your's do that also? If you hit the OD cancel button and drive in D3 mode, does converter clutch continue to come on and stay on ok at the appropriate time?

I will be back in the shop tomorrow and can check our computer data concerning sensor locations, but i'm a 30 mile round trip away right now

Dean
Dean @ TransLab and 6 other Dodge Specialists are ready to help you
Customer: replied 7 years ago.
Thanks for the help. I only see torque convertor lockup after overdrive. If it is happening in 3rd I can not see it. I will try driving with the overdrive locked out and see if I can tell if it locks up. Anyway the lockup occurs at around 50 mph when the trany is in 4th. The firs time I drive the truck after it has cooled down the trany shifts through all the gears exactly like it should. after a few minutes of driving it will no longer shift into 4th. I have read about the many TPS problems and just about put a variable resister in its place to see is that would solve the problem but as yet have not had the time. The main problem for me is I cannot find a good guide on the PCM that tells how to troubleshoot these kinds of problems. I cannot tell if the coolant temp sensor can cause this or if I am just wasting time trying to fix it. It sure may be the tps but it looks smooth when I move the throttle from idle to WOT. Thanks again for the help.
Expert:  Dean @ TransLab replied 7 years ago.
well, pragmatically speaking, no. you are not wasting your time. You need to eliminate the trouble code anyway. As i said, i'll double check the CTS location on the 96 tomorrow.
As for temp causing the problem, usually when the engine is colder it will tend to delay shifts unless you are up on your power range. The 12 valve pulls it's hardest around 1800 as you know (the 24 valve up to almost 3000). But the vehicle should have 4th gear even if the CTS is not getting up to temp correctly. If it was falsely reading overtemp, it still should not eliminate 4th since at cruise 4th pulls rpms down and with lockup on the engine should run its coolest (low rpm high road speed, plenty of air flow). SO, for that reason i was suggesting the toggle switch for remote ground to make sure the trans HAS 4th capability even if the TCU is not providing the ground.
If it does NOT have 4th / hot when you toggle it, there may be a problem with the OD solenoid or OD relay valve in the valve body or something like that. A solenoid swap is not a big deal and can be done from the bottom without pulling the trans. 11 bolts hold the VB on, and 3 screws hold the OD/LU solenoid assy.

do the toggle test as soon as you can, and i'll help you along till you get it fixed.
as for the controler info, i have the pin-outs and all that stuff and can help you as needed. the only problem i have is that i don't have my external drive here at the house,
and it has all the alldata and mitchell on demand, etc, as we recently relocated and its in storage. but the shop has everything. so we can get you fixed over a few days. no problem.

Dean
Dean @ TransLab and 6 other Dodge Specialists are ready to help you
Customer: replied 7 years ago.

Dean,

I finally got the chance to do the check on the OD ground wire. I drove around with the switch installed and every time I went through the gears the transmission failed to shift into OD at 50 mph at light throttle. When I used the switch to ground the OD circuit it immediately shifted to 4th. I then switched it off and it stayed in 4th.

 

I tried to run the ECT thing to ground and at this point do not believe the PO118 code is valid. From what I can find the engine only has one ECT sensor for the instrument panel gauge which is working fine. The only other sensor seems to be on California engines with EGR system. Anyway the problem must be the PCM or the TPS. I need to figure out how to check the TPS assembly for problems. I checked all the cables and TPS voltage, and kick down cable and all seem to be fine. However when I am at 50 mph in 3rd gear and let off the throttle the transmission shifts to 4th. So for the only way I can make it work normally is to use the switch you had me add. By the way my transmission has the 8 wire plug on the transmission not the three wire connector.

Expert:  Dean @ TransLab replied 7 years ago.
> Anyway the problem must be the PCM or the TPS

i'd put my money on TPS.
here's the deal.. the crank vibration goes thru EVERYTHING. So, the point when you are at cruise at say 65 (if thats where you run the freeways) THATS where it will wear out. its the location you are at most of the time and also where the vibration will buzz the wiper and erode the resistive area. so use your graphing meter or DVOM and increase throttle very slowly and see if you find any eratic points in voltage at that throttle opening. typically tps volts will be a whole volt higher than it should and that would be equivalent to a 4-3 part throttle position.

oh.. and lockup should happen in 3rd but maybe a little later. Here's how you can detect it. As you accelerate, your tach will increase with road speed. take note if there is a point when the tach does NOT increase but speed does. a soft lockup can still still be detected by the solid coupling feel between gas peddle and chasis, if you know what i mean.

Dean