Anybody have a clue what this code is? Drove 5 miles to the store this afternoon, was there 10 minutes. Started the truck and the SES light appeared, my on-board system says its code 1643, but has no info. Best as I can find it is some sort of speed sensor code or wait to start code. My wait to start light is working.

From the FAQ section: P1643 Wait To Start Lamp Control Circuit. Hope that helps.

Yeah, I read that too, but what does it mean exactly? What is broken or needs to be replaced now?

1643 says it has to see the problem 2 consecutive times. I can look when I get back to work tomorrow. I believe it said it could be a burned out wait to start bulb or a short in the controller. If no one else knows, I'll check when I get to work tomorrow and print out the diag. chart and bring it home with me. I have ALLDATA at my shop. Or I can print it out and email it to you.

My 98 manual say same as r85, & text there refers to physical problems with Bulbs, shorts, & grounds, trouble shooting tree asks if other codes are present, and for you to command the glow lite test on with a scan tool and ignition off, also vague reference to glow circuit, if physical problem can't be found swapping of PCM is recommended