Knight

I'm bumping thread as I've encountered very similar situation to the OP car unable to start, currently unable to use my fob or emergency deactivation with keys (no immob light in the clock). A few differences to note:

My car actually shut down on me while in motion, mid corner to be exact. So fortunately nothing happened in terms of an accident.

We have done all the above checks per this thread, so far my immobilizer unit internally isn't showing any visual signs of being damaged. We also had to to use Lorne suggestion to bypass the alarm, however it keeps going back into alarm mode on it's own.

My question, if I have access to another 993 to test can I simply swap out the immob box, alarm are these units paired to the car's ECU or anything like that? I wasn't sure if it was simple plug and play.

jay@EZimmoblock.com

Immos and alarms aren't paired to the ECU, or each other, so you can swap units in from another 993, no problem.

Knight

Excellent!

After all these hassles and if I finally confirm an Immobilizer issue, I'll be very tempted to go with your bypass system.

jay@EZimmoblock.com

Of the 2 units, focus on the alarm unit. The immobilizer is only involved in starting the car. Once the car starts, its job is done, i.e., it has no role in shutdown. The alarm unit on the other hand can shut the car down because ignition 12v passes thru an internal relay. If that were to open or chatter while the car was running, the engine would definitely shut down, so that's one possibility. The wires or connectors carrying that signal in and out of the alarm box are another. You didn't say what year your car is but in 95's equipped with airbags, that signal also has to make it through a set of contacts in the airbag controller. Keep us posted.

Knight

My 993TT is a 1996 model with early 95 production date.

My challenge at the moment is the car will not start - but all power accessories work (window, radio etc), I have no ability to do the emergency immob deactivation as the immob doesn't even appear to be working. And as this thread initially started, my fobs aren't communicating. We will be going thru all the pins connected to the immob today and beginning to diagnose further. Swapping will be next steps too.

Shall keep you posted!

jay@EZimmoblock.com

When you say "the immobilizer doesn't appear to be working" do the door LEDs flash and doors lock/unlock when you press the FOB or just nothing at all? If true, it's also not sending an "unprime" pulse to the Alarm unit. meaning ignition 12v will be blocked to the ECU. This is sort of a separate problem than the sudden shutdown you reported, but if you're poking around the immo or alarm unit, try momentarily grounding the BR/GN wire. This will "unprime" the alarm unit and allow ignition signal to the ECU. The BR/GN wire is pin 14 on the immo and pin 2 on the alarm unit yellow connector (second one from the upper right corner). You don't have to disconnect the immo or alarm to do this, just apply a momentary ground to the wire. That'll also silence the alarm if you happen to trip it during troubleshooting. BTW, the fact that all power accessories are working is consistent with power not getting thru the alarm unit.

paranoidandroid

I had this exact issue this morning. Immobilizer wouldn’t respond at all but all lights, radio, etc was working.

turned out it was the battery. It read 12.5V. I hooked up a trickle charger and it immediately jumped to 12.8. Immobilizer responded.

new battery swap from interstate and it’s all good now.

Knight

So it turns out Pin 8 out of immob wasn't getting power, tracing this line eventually lead to a surprise fuse box that was in the frunk close to the ABS unit - supplies unswitched power to the DME, immob and other things. I believe this fuse box isn't very well documented anywhere too. And discovered what appears to be stress crack on the fuse, not burnt. Replaced this 60A fuse and the car has returned back to normal state, Everything started up, immob light ok, alarm working etc.

Whether there is an underlying issue from the fuse cracking or going out, will have to see over time. For years now I have been experimenting strange intermittent (like once per year) symptoms where the car would just stall at random, this may be related to it we shall see too.

jay@EZimmoblock.com

Of all the things that can possibly go wrong with our cars, that 60A fuse is probably the last thing to be concerned about. Intermittants are always tough. Hopefully you've put this one to bed. Good sleuthing.