Maury Wright
TechOnline

But how does the immobilizer technology work. There are no easily located details on the NXP site but it uses passive RFID technology. When the driver turns the ignition switch, what Philips called a basestation IC that's in the vehicle wirelessly powers the fob via the coil that you can see above the IC in Figure 4. If the system doesn't identify an appropriate RFID tag in two seconds it kills the engine. To get a new Sentry key, the dealer must program the system to recognize the tag in the new key.

Figure 5: Our soldering skills are a bit rusty but we reattached the battery clip to the pcb.
(Click on image to enlarge)

Not wanting to pony up for a new key, we dusted off our soldering iron and went to work on the broken fob. We tried to clean hole in the pcb with solder wick but failed. But we were able to heat the solder pool from the top side of the board and partially insert the pin for the battery clip into the hole. Figure 5 show the result. It's not pretty but it worked.

We also managed to break the solder joint in the back of the clip that doesn't rely on a through-hole pin. Figure 6 shows our fix and also a look at the repaired pin now along the left side of the clip.

Figure 6: We also repaired a broken solder joint at the rear of the battery clip.
(Click on image to enlarge)

Figure 7 shows the pcb with the battery installed. The clip is clearly not perfect. The repaired side, now on the right, doesn't sit as low as it should. But it does hold the battery firmly in place.

Figure 7: While the repaired clip doesn't sit as low on the pcb as it shoud, the clip does secure the batter and the repaired fob works.
(Click on image to enlarge)

Alas the fob broke after the warranty expired. I'm sure we'll experience another failure down the road. I'm surprised that such a product made with Daimler in charge of Chrysler was manufactured in such a shoddy fashion. The worker that inserted the original battery had to have known that the clip wasn't seated properly.

As for the design, we're not sure about several decisions. The vehicle owner should in all cases have the ability to disable the alarm. Moreover, keys should not cost well over $100, although it would appear that the hard costs should be much lower based on a design with such a simple pcb and a single IC. The engineers seem to have placed elegance above simplicity, and we're not sure the decisions paid off relative to potential costly key replacements and perhaps even repair of the basestation subassembly in the car.