I have a 99 3500 PU and I’m well versed on the lock-unlock problem between 40-50 MPH. I fixed that problem years ago, but now I have a new problem. Last winter my converter started to lock-unlock anywhere from 50-70+ MPH…..now comes the strange part. It only does it when the ambient temperature is below 45 degrees. I drove it all summer with no issues at all. As soon as the temp drops below 45 degrees it starts. No codes. Any ideas?

 

I had posted a similar problem but with the dampness. One thing i was told to check was the wiring harness for the trailer hook up. If they are worn and chaffing they will short out the torque converter like tapping the brakes while driving???

 

I didn't find any issue with the wires.

Any chance the themostate could cause this? Maybe if it was stuck in the open position?

 

Sorry for the delay. Not sure that it would be the thermostate. My truck is in the shop still after joining this site and trying to trouble shoot the issue myself. I forwarded some of the responses i recieved from the blog. The speed output sensor may be another culprit.

Matt

 

sounds like throtle pos censor,just fixed mine today tranny shifs fine have to bypass the ecm,facebook matt at ats diesel he gave me step by step pictured instructions,its called the 4th gear fix

 

have you found a fix for this issue yet, i have a truck doing the same thing

 

well my dads truck was doing about the same thing as you described and i finally found what caused the problem. it had metalic sludge around the end of the speed sensor. i cleaned it off and everything is working perfect. i wish me and the transmission shop could have figured that out eight months ago.

 

Mattiebob where is the speed sensor located

 

its on the driver side on the transmision tail housing. it takes a 1 inch wrench or socket to spin it out.