someotherguy
+1y
Passlock on these trucks began in '98. If the security light comes on flashing, then it's activated and that's what shut off your engine immediately after it starts. If it comes on and stays on, it's indicating a fault in the Passlock system but should still allow the truck to start.
Remote start setups on these trucks do require a bypass module to work correctly.
There are a lot of problems with Passlock once the truck gets some age on it. The typical problems are bad tumbler, bad connection at tumbler, bad connection at body control module (BCM), or steering column/ignition tumbler or BCM replaced without matching the two pieces or doing a security relearn.
Some people think the key has a "chip" in it like the old VATS keys that you could see the resistor, but it is not true; the '98-up Passlock system key is a normal key just like '97-down. On Passlock the "chip" is in the tumbler.
The body control module (BCM) is the black box with bright green harness socket, sits behind the dash a little bit above the driver's side of the transmission hump. The BCM also contains the theft deterrent module (TDM) which is what the resistor in the tumbler is in circuit with. Usually the BCM won't bone you unless you replaced the steering column or tumbler. When I do a column swap in these trucks, I try to get the BCM from the donor truck, but I'd only do this if the trucks were very similar - I'm not totally familiar with what all other functions the BCM provides.
I've heard, but don't know for fact, Passlock can be tuned out of the PCM - so if you're thinking about getting a custom tune, you should ask about it. It's really a problematic system that is difficult to get right once it starts failing, usually because the fault can be intermittent for a long time before complete failure.
Even with a bypass setup, you are still having to communicate with the BCM so if it or the connections are faulty, you haven't solved the problem with the bypass. The typical bypass unit takes over for the resistor in the tumbler to allow remote start without the tumbler being turned.
To sum up:
Normal operation: security light on steady before starting engine (bulb check), turns off after start.
Security activated: security light flashing after start, engine dies immediately after starting.
Security failed/bypassed: security light stays on steady after starting.
By the way, all the above symptoms are my conclusions based on direct experience with several of these trucks, combined with service info about this rotten system.
Sorry for the novel, just wanted to share as much info as I could on this because it can be a PITA to find answers.
Richard