More in depth to specific details than what I posted. I would agree this sounds pretty correct. Is it possible the frequency is stripped by the DESS module rather than the antenna, or could it be stripped by the ECM? If the DESS module is a 2 connector with 2 wires per connector, then the DESS is probably as you say a DC to pulsed DC only type unit.
Reading this, it kind of makes me wonder how transient RF is overcoming the antenna, if the machine is supposedly smart enough to pull the logic of the key code out.
In regards to the DESS module, if it failed and only supplied DC instead of pulsed DC then it would indicate a single item failure. If the antenna failed, which seems to be the DESS item within the key switch failed, then the key would not become excited, and / or the signal could not be read. Having a logic circuit in the key switch is possible but seems silly since the real on board computer is ultimately making the decision I would expect.
Then again, it is BRP and seems incredibly over complicated.
I have not read them closely yet, but I did notice some electrical checks in the maintenance manual.
As I understand it the only way transient RF will cause a problem is if it is carrying with it digital data that gets mixed in with the digital data stream being read from the key, or somehow causes the digital data stream from the key to stumble.
The antenna serves two distinct purposes. First it creates an electromagnetic field, like Billy explains, that is rising and falling. A DC pulse will do this. That rising and falling magnetic field induces a voltage in a coil in the key much the same as the transformer outside your house. That coil and the circuit tied to it then becomes a power supply to the key circuitry. The transmitting portion of the key chip then transmits a stream of numbers which the antenna picks up and sends to the DESS module. The antenna, in this mode, receives and captures the radio signal from the key. Think of it kind of like the rabbit ears on your old style TV. I'm guessing the DESS looks at the data stream and verifies that the data is good. It isn't going to know if the data is valid, only that it is formatted correctly, has the correct number of numbers, and that those numbers look legitimate.
The DESS sends those numbers to the ECM. The ECM has stored in it the serial number of the key and a table of numbers, called the rolling codes table. The rolling codes table is different for every key. The ECM looks at the rolling code coming from the key. If it is the next one in the sequence, or only a few later, for one of the stored keys, it gives the OK to start. The key and the ECM traverse the table of rolling codes one a time in the forward direction, and keep track of which code was the last one used. If it gets a rolling code that is earlier in the table than the last one used, it will reject it as being invalid. I'm sure the reason BRP suggests turning the key on and off repeatedly when the DESS occurs is to force the key to move to a later number in the table and maybe it will be close enough to the last used code to make the ECM happy.
I'll offer a some speculation here. One is your key somehow or another is getting into an electromagnetic field that activates the chip in it and it moves along in the rolling code table so far that the next time you turn on the Spyder, the code it sends it so far away from the last one the ECM used that it is seen as invalid. Another speculation is that the two keys you have have code tables where some of the codes are the same in both keys. If you use a different key maybe the code it sends is behind the last one the ECM used from the other key. This will cause the ECM to reject the key. Or, if two keys have a common rolling code in their tables the ECM won't know which key is in the ignition and throws an error. Another possibility is the key chip is faulty and does not traverse the code table correctly. This is unlikely, but possible.
A suggestion I offer to whoever is experiencing DESS failures. Before you have the DESS module or antenna replaced have the dealer cut you brand new keys and program them into the ECM. Delete the old keys. I don't recall seeing anyone mentioning that one of the attempted fixes was to replace the keys first. Reprogramming the keys with BUDS will do nothing to solve the problem. Why? Because all that programming does is tell the ECM to read the key and store the codes from it. If the key is defective, i.e., has a malfunctioning chip in it, reprogramming does nothing to it.
For the record, my 2014 RTS, sold new in August 2014, now has 5400 miles on it. I have not experienced a DESS error, except those I created by having a second key next to the one in the ignition.
