List of codes.

[Hyperti2]

Hey guys I have a 98 1500 4l60e I have a transmission issue.
I scanned the codes and they were
P0740 TCC Circuit Malfunction
P0785 Shift Timing Solenoid
P1860
My tach goes out and the light under the PRND321 Gear selector flickers or goes out.
The trans goes into limp home mode when it is acting up. Now it does not happen all the time which is making me think electrical.
Some times its fine and some times it acts up. So I was wondering where I should start. I was thinking just get a whole new wiring harness
and a Shift Timing Solenoid. I just wanted the opinions of you guys. Thanks.

 

[rhino]

Very common problem on these. It is the ignition switch under the dash. The ignition switch supplies the 20 amp transmission fuse with 12 volts. There, it goes from the fuse to the transmission. One single 12 volt wire on the E terminal supplies all of the solenoids with 12 volts. They are commanded on and off by the computer with a ground. There are quite a few ways to fix this problem. The easiest is to make a jumper wire and jump from another fuse to the transmission fuse. That will feed 12 volts to the transmission. Or you could replace the ignition switch under the dash. The best fix is to install a relay. It will feed a full 12 volts to the transmission on startup at all times. Here is a link to the relay we offer, or if you have time you can build one yourself. http://www.rhino-transmission-parts.com/gm-electrical/?logout=1

 

[Hyperti2]

Very common problem on these. It is the ignition switch under the dash. The ignition switch supplies the 20 amp transmission fuse with 12 volts. There, it goes from the fuse to the transmission. One single 12 volt wire on the E terminal supplies all of the solenoids with 12 volts. They are commanded on and off by the computer with a ground. There are quite a few ways to fix this problem. The easiest is to make a jumper wire and jump from another fuse to the transmission fuse. That will feed 12 volts to the transmission. Or you could replace the ignition switch under the dash. The best fix is to install a relay. It will feed a full 12 volts to the transmission on startup at all times. Here is a link to the relay we offer, or if you have time you can build one yourself. http://www.rhino-transmission-parts.com/gm-electrical/?logout=1

Wow that sounds like exactly what it is. The previous owner installed a jumper wire to a toggle switch as a temp fix I might look into those relays however because when I use my remote start it puts my check engine light on. Thanks Rhino.

 

[C1500stepside]

This sounds like mine only its happening all the time! I took it to a transmission shop and they aay that the ignition switch needs to be replaced and they want $300 to do it! Rhino you think installing that relay you mentioned above will fix the problem or should I just get it replaced?

 

[rhino]

The relay takes the place of the ignition switch. Its very easy to put on. I wouldn't replace the ignition switch, get the relay.