I know it’s kind of late to mention this, but I found a lot of situations where people had the same problem as me, so I wanted to post my solution and all the info I had on the problem to potentially save some people a ton of money and trouble.  It may apply to any GM car with Passlock II, such as a Pontiac Grand Am.

I previously owned a 2000 Chevrolet Impala stealth police interceptor.  It developed a strange condition where the car’s cluster would flat-line entirely, and if that happened, likely not start unless it wanted to do so.  The instrument cluster’s gauges would drop to zero, and the “message center” would flash LOW FUEL, SECURITY, SERVICE ENGINE SOON and other ominous nasty messages in rotation.  Essentially, all instruments would fail simultaneously.  If this happened and the car was turned off, it likely would not start; I don’t recall if it turned over or not, but starting was almost guaranteed to fail.

After much poking around on the Internet, I learned of the GM cars’ vehicle anti-theft system (VATS) known as Passlock II (or Passlock 2 and I think sometimes it’s called Passkey II).  Essentially, the car’s Passlock II security system would stop the car from starting if something was wrong with the system.  This system consists of the key/ignition lock cylinder, the powertrain control module (PCM), the body control module (BCM), the OBD-II connector, the instrument gauge cluster, and the built-in radio.  (Yep, all of that combined is the car’s computer!)

Here’s the trick about this system: all of these components (other than the ignition lock cylinder) communicate with each other via a one-wire serial data line which is referred to on wiring diagrams as “Class 2 Data.”  The problem with Class 2 Data (I’ll call it C2D) is that it is spliced together at multiple connectors, and any one of those splices could go bad and fail to relay the C2D signal to the next device in the chain.  In my case, the two purple wires running to the OBD-II connector, which linked the PCM under the driver’s side air filter box and the rest of the system, was failing to make a sufficient connection and the data would relay sporadically at best.

What does that mean?  Simple: the powertrain control module, responsible for essentially all engine control, could not talk to the computers in the car that handled instruments, lighting, door switches, bells, and so forth.  Unfortunately, that meant that the instrument cluster could not receive engine status information, and worse yet, the body control module would never talk to the PCM.  Passlock II requires that the BCM send a password to the PCM to enable engine functions.  Bad C2D connection between the two automatically means a guaranteed no-start condition and 10-minute no-start trigger, courtesy of GM’s Passlock II.

How did I fix it?  It’s quite simple, really.  I cut the two purple wires behind the OBD-II connector, spliced them both together with solder on BOTH sides of the cut, and communication was restored.  Every problem with the car was immediately fixed, and that was the end of the saga.  Sadly, this happened only after I rewired so many other things on the car that I had run short on options.  Hopefully I saved you the trouble.