Just wanted to share my experience in case any others out there have a similar situation (I'll bet there are).

2003 XC70 with no major problems except for the past 2 years, every 3 or 4 months, when I try to start it, I get no crank - just empty silence except for the door chimes and other usual chimes. Lights & all other interior/exterior electrical works just fine. After a week in the driveway trying to figure it out, I had it towed to the dealer who called me and said "What's wrong, it started up just fine". Nothing was fixed and there were no fault codes.

2nd time, same thing a few months later, I towed to different shop where they called me and said "What's wrong, it started up just fine". So I went to pick it up and when I did, it didn't start. GLORIOUS, right? These guys'll fix it this time! They decided it needed a new starter. That seemed to work.

Until...5 or 6 more times over the next year and a half. Same symptoms, except every once in a while I'll get the "Immobilzer, See Manual" or "Start Prevented Try Again" error message (but not everytime). Then it would just start, but I never know when or how or why. Now I have a car I can't rely on, and since I live in Alaska, I'm not too keen about driving it far from home. The guys at the shop replaced my antenna ring, and it seemed to work. We ruled out bad chips in my key (I have 3 keys and none of them worked). I tried everything I could find online - 5x unlock/lock with fob, opening driver door with key, setting the panic off, putting it in neutral, jiggling the key, flipping it over, removing/replacing CEM relays, fuses and a few more I'm sure.

About one month ago, the same thing and now I'm suspecting a deeper ECM/CEM issue or other electrical problem. I's been sitting in the garage for about 4 weeks. Then I found this video. and it started right up. I used CorrosionX to clean the connector on the solenoid/starter wire. That little connector didn't even look like a connector until I cleaned it up.

I really hope this is the final fix for this (I will be heartbroken if it's not), and I'll let you know if it's not. I've been reading every post related to this and just wanted to share my experience in case it might work for you too!

 

I am so curious about your fix! I know it has only been a few days, has it worked?

This EXACT thing has been happening to me...very sporadically not starting...about 1/5 of the attempts give me the Immobilizer message. One night left me stranded, the next morning acted like the battery was dead and nothing cranked, put the pedal to the floor and then it started? Have tried using both key fobs and that does not seem to be it. Weird, has nothing to do with cold temps, in fact, have been below zero for a week, the day we come out of the deep freeze, it doesn't start.

I am on the cusp of another $800 bill (following $1400 to change out spark plugs, hoses, belts, etc) to change out the fuel control module from the rear wheel to inside the car, though I am not totally confident this is the issue. Please tell me if this has worked for you so far!

 

Yes - it is still starting up everytime. My symptoms were the same as yours - I even drained the battery trying to start/flip keys/changing gearshift/unlocking & locking/etc. when it was very cold outside and had to charge it back up.

I had my car in the garage for 4 weeks trying every day or so to see if I could get it to start, so I could take it back to the shop, and after cleaning the starter connector, it fired up just like normal. I'd like to think the simplest solution is the correct solution. Kinda like checking to see if your computer is plugged in when it's not working.

Good luck - I'll post back if my car doesn't start again.

 

I know this is an older post but my '03 xc70 has been plagued by the immobilizer issue on and off since day one. I have owned it since new and now it has been handed down to my son. The dealer installed a new antenna ring but it still randomly happened. I installed a new starter. Same problems. Then I noticed something strange. Every time the immobilizer issue cropped up, it was when I would have a bulb out somewhere on the car. Didn't matter which bulb. Headlight, brake light didn't matter. For the past 5 years I have kept a spare of each bulb in the glove box and would replace any bad bulbs instantly. Never had the problem again.

Not sure if this has been brought up before.
Sounds strange but it works for my car.

 

If the car throws multiple error messages (immobilizer, AWD, brakes, etc.) then it's possible the problem is a dead battery. New battery fixed it for me. I got the car started after a recharge and drove it for 20 mins, no problem. But afterwards it wouldn't start, indicating that the charging system, though working, was not charging the battery.