Overdrive ckt....

[BHerring]

Hi all,

Hey... . I need some help with the overdrive circuit (ckt). I can’t tell if my truck is going into overdrive. First thing I tried was the OD switch on the instrument panel and the transmission did not sift into 3rd. I pushed the button several times with no luck. During normal driving conditions I cannot tell if she is going into 4th (OD). I did read the Dodge Service manual and I know the fuse is good. What I need help is the wiring diagrams. I also know there is the transmission temp and coolant temp that enable the OD. I need to know the signal flow or what the sensor enables. I know the OD solenoid is on top of the transmission. When I have OD on what should be at the transmission solenoid? This is most likely a simple ckt, I just don’t understand / read the factory wiring diagrams. Any and all information will be greatly appreciated.



Cheers,

 

[cerberusiam]

Easiest way to tell is run it up to 60 mph and if the engine screaming its not going into OD.



Manually shift up thru the gears so you can feel the shifts. You will probably find you are going to drive and thats it but you should be able to feel the OD shift or at least the engine quiet down.



You will find a 2 wire plug on the transmission about the middle on the drivers side that is a vertical plug not horizontal. That will be the power supply and OD sense wire. The larger of the 2 should have 12 volts with the key on. Check that first.



The smaller of the 2 wires is the OD sense wire the PCM grounds to activate OD. Tap it wth a scotch lock and run the wire to simple toggle switch in the cab with the other pole of the switch to ground.



When you engage the switch you should have OD. If you do its a PCM, speed sensor, TPS or other electrical glitch problem. If not and you have 12v at the trans its probably the solenoid.



Try that and see what the results are.

 

[BHerring]

Ok.

I am pretty sure the transmission is auto shifting into OD, because I can do 75-80 with about/close to 2300 RPM.



When I am going about 55 or 60 I will push the button/switch on the instrument panel to turn off OD the transmission stays in OD, it will not shift from 4-3. I also was going about 55 or so and floored the pedal to see if the transmission will auto down shift 4-3 but that didn’t happen either. I also tried different speeds up to 65 and she would not down shift from 4-3.



How and where does this switch tell the transmission to turn off OD. Does the switch provide a ground to the OD on/off solenoid or does is provide the ground to the PCM??



Cheers

 

[cerberusiam]

The switch on the dash is just a momentary switch that flips a gate in the PCM to unground the OD circuit. Sounds like the momentary switch is not working correctly back to the ECU. Does the switch light up when you try to turn OD off?



Can you get it to downshift at say 40-45 mph or does it just dog along until the turbo spools?



The 4-3 shift is a little harder to tune unless the TPS, kick down cable, and trans pressures are all within a narrow margin. Any of them get too far out and OD is either in or out and not a lot of leeway of when. Might try checking your TV cable too make sure you are getting good movement when you floor the throttle.

 

[BHerring]

Yes the lamp does light up



The transmission will downshift sometimes and then sometimes just dog along until the turbo spools, so I gues the answer to this is could be yes and no. .





I adjusted the TV cable according to the Service Manual.



I need to trace the ground or open from the switch to the ECU. What pin on the ECU recevies the ground / open from the dash switch.

 

[BHerring]

UPDATE:



When ever the transmission shifts into 3rd (around 35-40 MPH) and I increase the speed to 45 or so and floor it the transmission will NOT downshift to 3. So I am thinking when ever its shifts into 3 its must shift into OD very shortly later. I do remember when ever I would floor it on a long interstate on ramp, it would shift into OD around 55-57 mph, now its doesnt shift.



Off to the garage to take some voltage checks and will let you know.

 

[BHerring]

Update #2



With the key on and the OD switch on I have 12 volts on the blue wire (big) and O volts on the smaller wire.



Nothing changes when I push the switch on the dash. . so I have no idea what to look at next



Cheers

 

[cerberusiam]

Update #2



With the key on and the OD switch on I have 12 volts on the blue wire (big) and O volts on the smaller wire.



Nothing changes when I push the switch on the dash. . so I have no idea what to look at next



Cheers

You will need to test it driving. The ECU won't apply OD until the trans is in drive, the fluid temp is above a preset, TPS voltage is correct, and there is a speed sensor signal.



Like I said before, tap that second wire with a switch to ground to verify solenoid performance then work back. Have you checked your TPS voltage at rest and across the throttle opening range? Look for the top and bottom values and a smooth rise. Could just be a bad TPS.

 

[BHerring]

cerberusiam,

I want to thank you for helping be out!!



I will tap the second wire this weekend and will do a test when the truck and transmission are all warmed up.



What should be the values for TPS when at idle and at Wide Open Throttle?

 

[cerberusiam]

cerberusiam,

I want to thank you for helping be out!!



I will tap the second wire this weekend and will do a test when the truck and transmission are all warmed up.



What should be the values for TPS when at idle and at Wide Open Throttle?

Every truck will vary someon what it wants to work correctly but a general place to start is . 8 volts at rest and 3. 5 volts at WOT.



The 3. 5 volts I have found to the absolute max on my truck and cause a very late shift to OD, like about 65-70 mph. Almost useless at WOT as its is almost into defuel to shift. I use the venerable mystery switch when I want it to work right.

 

[BHerring]

update. . again



I hooked up the control wire to ground (while driving) and it still didnt shift to 3 ( I tried it numerous time with ground and with out). So I guess your going to tell me its time to drop the transmission pan and check out the OD soleniod... . right...

 

[cerberusiam]

update. . again



I hooked up the control wire to ground (while driving) and it still didnt shift to 3 ( I tried it numerous time with ground and with out). So I guess your going to tell me its time to drop the transmission pan and check out the OD soleniod... . right...

If you mean it did not shift to 4th (OD) then it sounds like a solenoid problem. It won't work unless you ground the sense wire but if you ran the tap thru a switch and verified the switch was working correctly then it sounds like it is time to drop the pan. You can first check to make sure the harness is connected in the pan and proceed from there.

 

[BHerring]

Heres my problem, I think we are working in different directions:



When I am normal driving the transmission will auto shift to OD (4th gear) but when ever I push the button on dash or floor it the transmission will shift down to 3rd. So I assumed that when you ground the wire going to soleniod then you created a current path and the solenoid will open or (close) causeing the transmission to shift into 3rd. Is this correct or not?



Anyways when ever i grounded the small wire on the soleniod the transmission didnt do anything, even when I opened the ckt (removed the ground) the transmission didnt do anything.



Is this a problem inside the pan or not?

 

[cerberusiam]

Heres my problem, I think we are working in different directions:



When I am normal driving the transmission will auto shift to OD (4th gear) but when ever I push the button on dash or floor it the transmission will shift down to 3rd. So I assumed that when you ground the wire going to soleniod then you created a current path and the solenoid will open or (close) causeing the transmission to shift into 3rd. Is this correct or not?



Anyways when ever i grounded the small wire on the soleniod the transmission didnt do anything, even when I opened the ckt (removed the ground) the transmission didnt do anything.



Is this a problem inside the pan or not?

Ahh, the little light bulb over my head is now glowing.



When you ground the OD sense wire it energizes the solenoid to engage OD. To lockout OD you need to break the circuit on the OD sense wire. That will require cutting the wire and running it to a double pole single pull switch and wiring it correctly.



When you push the button on the dash it should downshift to drive as will flooring the accelerator at anything uder 60 mph generally. Is this your normal behaviour?



Are you just not feeling the shift to OD or only feeling 2 shifts instead of 3 and that is what is making you think it is not in OD?



From your original post I thought you were missing OD entirely and were trying to verify the solenoid would work. Please correct me if I misread the problem.

 

[BHerring]

When ever I push the button on the dash the transmission doesnt downshift to 3rd from OD



When ever I floor accelerator the transmission doesnt downshift to 3rd from OD. I know the transmission up shifting to OD because I can go 80 MPH.



I disconnected the plug going to the soleniod (12 volts and sense wire) and I have no change, the transmission shifts up to OD and if I push the button on floor it (under 60 mph) the transmission stays in OD.



So I need to know how to troubleshoot the no 4-3rd downshift, either from the dash switch or flooring the pedal.

 

[cerberusiam]

I disconnected the plug going to the soleniod (12 volts and sense wire) and I have no change, the transmission shifts up to OD and if I push the button on floor it (under 60 mph) the transmission stays in OD.

The only way that can happen is if the solenoid is jammed in the on position or there is a problem in the OD circuit shunt. The solenoid has to activate to activate OD in normal operation. If you are getting OD with the power and OD sense wire unplugged there is a VB problem.



Just checking to make sure that you did do a manual shift test test starting in 1st and you can feel 3 distinct shifts, 1-2, 2-3, and 3-4, as you shift up thru the gears. With the TV tightened up and about half throttle they should be very noticeable.

 

[BHerring]

I concur with you that the problem is in the VB. Will be checking it out this weekend.



I do feel three distinct shifts~