Hi, i have a 97 dodge automatic that has stopped shifting into overdrive. For a short while prior to this it would shift periodically into overdrive. Tranny replaced approx. 60,000 miles ago. I have rebuilt throttle assembly (needed it anyway) along with new TPS. Could there be a vacuum problem, relay, computer, etc.? Any help would be appreciated. Also voltage guage doesn't seem to move no matter whats running, doesn't discharge just stays on center...Thanks..

 

The most common problem with an erratic overdrive is that the throttle valve cable has a loose end or broken clip on the housing on one end or the other, either down by the transmission or up by the injection pump. Some have a plastic loop on the inside cable ends that cracks and looks good until you move it, then it opens and will not allow the cable to move far enough to properly regulate the throttle valve in the transmission to enable shifting into overdrive.

The next most common problem is a floating ground. This is where the body to frame or engine to frame ground straps have rusted or corroded and lost contact.

Next on the list is the TPS is faulty or needs adjustment.

There are also relays and fuses in the power distribution center that fail once in a while.

The wiring harness from the transmission also can get corroded or dirty.

Additionally, if you had the transmission rebuilt and a shift kit installed, the throttle valve will not actuate enough and it will be necessary to install a resistor at the TPS to obtain the proper voltage to enable the logic to recognize the correct setting to enable shifting into overdrive. Any of the decent diesel transmission shops carry the resistor kit.

 

Thanks RCW, I appreciate the time you've taken to answer my question. I'll start from the top and work my way down according to your post and let you know. Once again thanks.

 

You should also check the transmission temperature sensor. If you want to check it you can unplug the connector at the tranny and put a 1000 ohm resistor between the two wires. This will allow you to at least check the operation of the sensor. The resistor will "fool" the computer into thinking the transmission is aways at operating temperature.

 

Thanks sidewinder, I'll try that too...I really appreciate it!

 

I have the exact same problem. no overdrive. Mine was normal then just stopped. I have tried all of the above to no avail, everything seems fine. My trans was rebuilt about 50,000 ago. truck is a 97. TPS is fine, I adjusted tv cable but it was pretty close to perfect anyway. temp sensor fine. no codes. even ran a new ground even though old ones are in great shape.
Any other ideas?