Engine/Transmission (1994 - 1998) No overdrive and no cruise control

[WadePatton]

It's awful greasy under there. :-laf



Well for those that don't know the rest of the story. My wife just left me a few weeks ago and I'm hogtied to the business here---that's why it takes me a day or two to check this or that.



So I will check the integrity of the circuit. I'll bet that it's okay because when I put the bad resistor in--the light came on. With a good resistor it's off. But I could be full of mud.



I have a stock transmission in the shed--wonder if the OD unit in the Suncoast is stock?... BUT then I'm going to convert this truck to a 5-speed when my clutch/shaft envelope gets full. I have a 4500 and donor truck waiting patiently.



Thanks all, I'll keep fiddling with it as I can.

Wade,



If your ohm meter is working, check the black wire on the ground side of the temperature sensor to see if it is really grounded.



The temperature sensor, when cold, applies a high resistance to the OD control circuit at the PCM. As the sensor temperature rises it's resistance drops and at some point, allows the transmission to shift into OD. lf the grounded side of the sensor is open, the transmission will not shift into OD no matter what resistor you put in.



Also, if the wire between the PCM and the sensor is open, that will have the same effect.



In that case, you could find the wire where it comes out of the PCM and attach the 1000 ohm resistor between it and ground.

 

[Howard Durand]

Since nothing seems to make the OD shift, you might have an open or shorted OD coil in the transmission or a mechanical problem with the actuating mechanism.

With a volt/ohm meter, you can check the coil and wiring to see if they are OK or not.

 

[NKenny]

I have recently begun experiencing very similar issues. Did any resolution ever come to this Wade??



Last Wednesday, I noticed the truck was having a difficult time getting into overdrive and the truck was hunting between lock and unlock in 3rd gear and in Overdrive if it would ever get there. Shift quality was poor as well. I took the truck down on Saturday to change the transmission filter and fluid, adjust the bands, replace the TPS with a Potentiometer, and check the suspect wiring of the mystery switch.



Reuslts included much improved shifts and reliable lock-up with the mystery switch in 3rd gear. However, I cannot get it into OD at all and I noticed this morning that the Cruise Control is not funtioning. CC was working last week prior to taking the truck down.



I have checked the brake switch by lifting the brake pedal once the truck is at speed... No shift. I have tried different settings on the Pot. with no avail (although I noticed that if I turn the pot all the way left, off, the speedo falls to zero and a check engine light flashes once very quickly. I was getting an intermittant transmission Temp light for the last two weeks but the guage showed normal operating temps.



Thanks in advance.

 

[Howard Durand]

Did you check the transmission temperature sensor or replace it with a resistor? A bad sensor will prevent OD engagement and probably cause the intermittent temperature light. The potentiometer turned fully left will normally still allow an OD shift but will prevent normal TC lockup. Not sure why the the speedometer drops to zero. With my potentiometer setup, turning the pot all the way left reduced the signal voltage to about 0. 8 volts which is below normal. If you use a potentiometer without any resistance between the low end and ground, turning knob fully CCW will ground the signal which I have never tried.

 

[NKenny]

It probably grounded the signal. I thought the Pot had a resistor on the low side, but I could be wrong. I may well have the wrong leads in the wrong place, please advise (My Pot)



I bought a 1K resistor this afternoon to put in the temp sensor. Just got home and haven't tried it.

 

[NKenny]

Update...

I installed the 1K Ohm resister in the transmission temp socket to no avail. No difference.



Is there something that could be stuck or sticking on the OD off button? I had my BIL replace the OD off button with one on the stalk and I got to thinking the wires may be wrong. I noticed that it didn't work once I started driving the truck, but the truck still shifted into OD. Now, it goes into 3rd and will only lock the converter with the mystery switch.

 

[NKenny]

I need some input on where to look next. Still no OD. Cruise seems to work if I hold the buttons just right, so I will assume it is in the contacts.



Am I looking at solenoids near the valve body, overlooked fuses / connections?



I am driving this truck way too many miles to not have OD; ~75-100 a day with my '01 down.



Thanks in advance.

 

[Joe G.]

I don't know if I can help or not. If you press the OD button does the OD light change states? If it does not then you probably have a bad switch set up. The light is controlled by the PCM. The button has no direct connection to it in spite of being on the button assembly.



The button puts a ground on the OD wire to the PCM. Each time it is pressed the PCM changes the OD state. If there was a ground to the solenoid (OD on) the PCM removes it. If there is no ground (OD off) the PCM applies one. This, of course, depends on if the truck is going fast enough for the PCM to apply OD.