For me, the problem happened on a semi-frequent basis -- maybe once every ten tries? I tried switching to my spare Pathy key, which was pretty much brand new, and the problem went away. I never investigated the issue further. I was thinking of spraying out the ignition lock cylinder with some electrical contact cleaner, and then some silicon (or other dry lubricant that doesn't leave a film behind, like graphite) -- the intermittent problem suggested a bad contact between the key and whatever electrical contacts detect the chip in the key. But never got around to doing that.
There is a module inside the steering column, the NVIS Immobilizer module (aka IMMU) sitting on top of the ignition lock cylinder, and there are a few fuses (62, 24, 16). These may be the problem, or it could just be a faulty key or dirty contacts in the cylinder.
Oh, and if you try pulling OBD-II codes in the near future and see any of the codes [P1610,P1611,P1612,P1613,P1614,P1615], those are codes related to the NVIS / anti-theft system. They won't trigger the check engine light, but will stick around for a while. (P1614 is what I had -- "IMMU cannot receive the key ID signal").
A side note: If you try and start the QX4/Pathy and it fails five times in a row due to the NVIS system, it'll go into "lock mode" and you won't be able to start it even with a good key. If you have a scan tool and pull the code P1610, this means you're stuck in lock mode. To reset and get out of lock mode, perform the following steps:
1. Turn ignition switch off.
2. Turn ignition switch on with good key. Do not start engine. Wait 5 seconds.
3. Turn ignition switch off.
4. Repeat steps 2 and 3 twice (total of three cycles).
5. Start the engine.
There's more info in the
factory service manual (in the Electrical System section), but a lot of the steps involve using the CONSULT-II tool that the dealerships have. There's not a lot of testing/diagnostics a DIY mechanic can do.
