Immobiser Parrasitic Draw Checking for Sleep Mode Shutdown.

Simple way to use a scope to check if immobilizer is going into sleep mode --- captures are from a BMW EWS 3 immobilizer.

Basic schematic.



Home made pick-up coils. 3 turn and 9 turn coils wound using wire from old computer network patch cable, coil diameter has to be just large enough to fit around key, more turns of wire gives higher voltage but I found it works nicely with just a 3 turn loop..



Above simple home made pick-up coils,




Above EWS Immobilizer in sleep mode --- close to zero volts.



Above System awake key in steering lock , unlock buton pressed.



Above Key removed after a few minutes system goes back into sleep mode.

Question,

If you run into an immobilizer issues, say a crank no start or no crank and want to make sure its not a key problem, does the system wake up regardless if the correct key is used or does it only wake up when the correct key is used. Maybe it differs from vehicle to vehicle.

Only tested so far on the BMW EWS3 system --- anything that wakes up the body computer or engine computer or light switch makes the security system search for a valid key transponder, but for road safety reasons it only immobilizes the system at start up. So if a valid transponder code is passed at start up the engine will start, then if the transponder chip is moved away from the ignition lock the engine will continue running but not allow a restart if stalled.

When the the key is turned in the ignition the engine computer requests a valid ""Okay to start" rolling encrypted code from the EWS3 security module, if the correct token isn't passed the engine is immobilized. Most older system weren't as secure in that the engine ECU would hold the valid code until it was over-written.

The BMW EWS3 was quite sophisticated system when it was introduced back in the late 1990's. One of the interesting features is the vehicle odometer reading is stored in the key, it is also stored in the instrument cluster (BMW call it the IPK) and the light switch module (LSM).

I've found that a way to force a unit or units to go to sleep, when a parasitic draw caused by a unit not going to sleep is suspected, is to short the communication lines to ground. A lot of times this can even be done right at the DLC, which is nice. If the draw goes away, one of the units in the network is staying awake. It's a quick check, so to speak.

I love your post btw. Great idea, thanks for sharing.