Specifications
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Testing Testing Immobilizer (EWS) Systems
z To perform an alarm quick test:
• Press the lock button twice.
This should deactivate the alarm motion and tilt sensor. If the alarm now activates, check for
a faulty alarm motion or tilt sensor.
4.10 Testing Immobilizer (EWS) Systems
EWS stands for the German words “Electronic Wegfahrsperre” meaning electronic drive away
protection. Starting in 1994, BMW vehicles came equipped with EWS, which disables fuel and
ignition using door locking input from the General Module to the DME.
There are three versions of EWS currently in use:
• EWS I
• EWS II
• EWS III
4.10.1 EWS I
Beginning with the 1994 model year, all cars were equipped with EWS I. This system still uses a
mechanical key but added a “Starter Immobilization Relay” preventing the starter from operating.
It functions as a smart relay which only allows starting if a specific combination of inputs is met.
The EWS I system is activated when the vehicle is locked from the outside with the key. When
activated, the EWS I system performs the following functions:
• Prevents the engagement of the starter
• Disables the fuel injection system
• Controls the neutral safety switch
4.10.2 EWS II
At the start of the 1995 model year, EWS I was replaced with EWS II, which is used on E31, E34,
E36, E38 and E39 vehicles. EWS II incorporates all of the functions of the previous EWS I but
uses an electronic key. There still is a mechanical key, but an electronic component was added
interfacing to the ignition switch which is part of the EWS function. EWS II provides immobilizer
protection electronically through a coded chip imbedded in the key and prevents vehicle operation
until the ignition key has transferred the correct code (random changing code) to the EWS control
module. EWS II permanently assigns an “Individual Serial Number” or “ISN” to the DME, which is
also stored in the EWS. The DME and the EWS modules must match the “ISN” every time the
ignition is powered on or the engine will not start.
With EWS I and EWS II, the DME and the EWS are not permanently married or locked together.
Diagnostic testing with either a used DME or EWS is possible (EWS II will require the ISN
alignment procedure outlined below).