Engine/Transmission (1998.5 - 2002) OD lockout button not working.

[SnoKing]

Today I had a problem in that the OD lockout button lights the light on the dash, but it will not take the transmission out of OD. The DTT smart controller will switch back and forth to OD and 3rd without a problem. If I lock OD out before I start out, then most of the time it will stay in 3rd until I push the OD button again, and it shifts into OD, if I push it again, it will not lock out OD. If I slow to the setting in the DTT smart controller it switch out of OD every time. Help! Off to read the service manual. SNOKING

 

[SnoKing]

OK, I am learning more about how the 3rd to 4th shift works and the circuits. So this is the deal. The PCM or smart controller grounds the brown wire going to the transmission to make the 3rd to 4th shift. Pushing the OD lock out buttom removes the ground and solenoid drops and transmission down shifts to 3rd. My issue is that the PCM output on the brown wire is not going all the way to float and the voltage stays at around 9 v on the brown wire. This is enough to keep the solenoid picked and it will not shift out of 4th. So it looks like a PCM issue. I sprayed cleaner of the three plugs and put dielectric grease on them and cleaned the PCM ground strap on both ends. Same issue.



Anyone have a PCM that I can try in it. I live 70 miles North of Seattle in La Conner.



I am also waiting to talk to Bill again.



How much does a PCM cost?



I remember someone posted recently about a place that sells ECM's and PCM's.



SNOKING

 

[SnoKing]

OK, appears that it is the PCM. I wired a switch in the place of the lead from the PCM going to the smart controller, and I can effect OD the same as the OD button on the shift lever, but with out the dash light. Sure would like an old auto PCM to take apart and look at it. I am a trained Electronics Engineer, and might be able to replace the out put component and save it. However, I do not want to pop open the one on the truck just yet. Marco do you know anything about the circuits in the PCM?????



SNOKING

 

[SnoKing]

Anyone got an old PCM that I can take apart? SNOKING

 

[DFerverda]

I don't remember for sure but i think this is the link that was posted here a few months ago. Wish i could help more.....
OEM Computers For Dodge By Auto Computer Exchange
Dirk

 

[SnoKing]

Come on someone must have an old PCM in their garage. See my add in the classifieds, I will post pictures and a write up if I can fix my PCM myself. But, first I would like to look in one before I open mine!



SNOKING

 

[SnoKing]

OK, appears that it is the PCM. I wired a switch in the place of the lead from the PCM going to the smart controller, and I can effect OD the same as the OD button on the shift lever, but with out the dash light. Sure would like an old auto PCM to take apart and look at it. I am a trained Electronics Engineer, and might be able to replace the out put component and save it. However, I do not want to pop open the one on the truck just yet. Marco do you know anything about the circuits in the PCM????? SNOKING

Well after five years of using the DTT smart controller and a manual toggle switch on the side of my CB in front of the center seat I decided to try a little electronic test. Background: transmission would shift into OD normally by the PCM grounding the lead to the overdrive solenoid. However the PCM would not shift it back out of OD by floating the lead to the solenoid. Measurements showed the the PCM output lead would not go to float to drop the solenoid. I found 10.7 volts on the lead and with 14+/-V on the other side of the solenoid it would not drop out. So today I put six 1.5 amp rated diodes in series in the lead from the PCM.

Knowing that most diodes have a .5V voltage drop, then six would be around 3V. So with 10.7 + 3 volts the voltage on each side on the solenoid should be about the same and the solenoid should drop, right? The next question was would the solenoid pull with 11 volts vs 14 volts.

Well it worked! The overdrive button works normal again and with the DTT controller off the PCM will switch the transmission in and out of OD normally. Diodes had to be installed all in the correct polarity for this to work.

I had also installed a relay in the OD circuit back when as the PCM's lack of float and the fact that DTT removed the transmission relay and installed a jumper to bypass it caused a battery drain.

Now DW can drive the truck without the smart controller and exhaust brake if she wants. Chris