Viper 4806v Sierra 1500 Dies Immediately

Viper 4806V 2007 GMC Sierra Classic with zero options (no alarm, no locks, etc.) Issue: When I hit the start button, the starter fires up and the truck starts but then immediately dies. If the key is On it starts up just fine. I'm pretty sure it started up correctly one time, because I think I stuck the key in and I know I rotated it and had a slight panic when turning the key off didn't turn the truck off. After that I set about hooking the brake wire up and it hasn't worked since. The only error I get is 'Low/No RPM.' I get voltage on the tach wire after start, I have the machine set to real tach, and I've ran the tach learning program several times. But even if I set it to virtual or 'off' it does the same thing. Using this nice guide to help determine which wires are which. I've quadruple-checked (if not more) the correctness and continuity of my connections. Any hints?

I should add that when it didn't work after connecting the brake wire, I disconnected the wire again. Pretty sure I didn't change any other settings at that time.

Disconnect the brake wire, and see if it stays running. If = yes, you have the brake wire hooked up to something that powers up after it is running, and shuts it off. You should be getting a "brake" shutdown code though. If it isn't the tach, the brake shut down will behave the way you describe. Actually, tach usually runs for 5-ish seconds then shuts down. Brake shut down is instantaneous.

davep. wrote: Disconnect the brake wire, and see if it stays running. If = yes, you have the brake wire hooked up to something that powers up after it is running, and shuts it off. You should be getting a "brake" shutdown code though. If it isn't the tach, the brake shut down will behave the way you describe. Actually, tach usually runs for 5-ish seconds then shuts down. Brake shut down is instantaneous.

Tried it. Like I said, I immediately disconnected the brake wire but it didn't help. I don't get a brake shutdown error, just 'Low RPM.' But you're right, it's not acting like the tach problems everyone else is talking about. It's like the ignition is being cut. I've monitored both ignition wires and they keep 12v for the 5 or so seconds that the Viper waits before a tach reading. I think the Low RPM warning is coming from that reading, not from the truck shutting off. With that said, I think it may simply be that my Passcode bypass isn't working. I thought that it wouldn't allow the ignition to come on at all but an immobilizer is one of the solutions that's in the troubleshooting manual.

Yep, that was the problem. The truck's Passlock system was shutting it down. I dug up some resistors and bypassed it. Thanks for helping, Dave.