Overdrive not working.

[Rattler]

My son just brought home a 93 auto truck, and he said the overdrive wasn't working on it. What controls overdrive in a 518 trans? Is it the valvebody or the computer?Randy

 

[dodgenstein]

Overdrive is controlled by a solenoid in the valve body through the computer. The computer must get proper signals from the crank position sensor, a couple of temp sensors, a vehicle speed sensor, and most troublesome, a throttle position sensor. In addition to taht trans pressures must be right and the OD clutches must hold.

 

[Rattler]

Thanks, that might give me somewhere to start. Has anyone wired the OD for a switched on-off if there was a problem elsewhere in the system. ? Randy

 

[PToombs]

Yup, lotsa guys. Just put a switch in the return side to ground. The 'puter just grounds the circuit if all the other stuff says it's ok. You have to check the schematic, I'm not sure on the wire colors. Sorry about that.

 

[Rattler]

Thanks Pete, i'll tell my son but i'm sure that it will be me that ends up fixing it. Randy:-laf

 

[cerberusiam]

You should have 2 wires in the OD control harness, one will have 12 volts on it with the key on so the other smaller wire is the OD sense wire.



Check and make sure you have 12 volts there to start with. Thats is driven off a relay that can sometimes go bad. Without power no OD.