BMW EWS – Electronic Immobilizer on CAN-bus BMW motorcycles

EWS failure has been known to be an issue with the R1200GS (and other BMW motorcycles). This article should help you understand what the EWS system is, how it works and what happens when the EWS fails. There is also guidance on how to get your bike running again in the event of an EWS fault or failure but you will need a spare (good) EWS / RA – Ring Antenna unit.

Update Aug2009 – “Just wanted to share that the new EWS antennae keep failing. Had it replaced in my bike today and the dealer told me that just this day he had two other beemers lined up to have it fixed as well. All ’09 models” Ognacy. ADVRider.com

NB: Ring antenna service recall by BMW applicable to certain models from 2007 and 2008 models until March. Owners have been notified by a BMW letter.
Part number (old) : 61 35 7 696 463
Part number (new) : 61 35 7 705 247 (costs in Germany Euro 23 ~ US$ 35)

BMW EWS – Electronic Immobilizer on CAN-bus BMW motorcycles
Article by HexCode
(www.hexcode.co.za – makers of the GS-911 BMW motorcycle Diagnostic Tool)

What does “EWS” stand for?
EWS is German for “Elektronische Wegfahr Sperre”

The most common symptom of faults and failures:
The motorcycle does not start and the “EWS” is intermittently or permanently displayed on the instrument cluster (KOMBI)
Precursors to EWS failure sometimes occur by way of intermittent faults for some time before the bike does not start at all – won’t idle, poor throttle response, knocking, running hotter, hesitation.

Battery charger
Are you charging your bike with a CAN-BUS compatible charger? Make sure you use one to reduce the chances of your CANBUS system having a failure.

The problem
Since the systems inception in 2004 it has been plagued by various problems, the biggest by far being the (un)reliability of the Ring Antenna and Evaluation electronics.  This of course is a single point of failure and if it does not work, there is NO chance of authenticating the Ignition Key and no chance in hell that your engine will start and run.

The Fault Code diagnosis
According to several dealerships and dealer techs we spoke to, a faulty ring antenna raises a Fault code within the BMS-K(P) only 50% of the time…

General description of the EWS system in CAN-bus based motorcycles
The electronic immobilizer consists of 4 parts:

When the ignition is switched on, the Engine Controller initiates communication with the transponder chip in the key. Data is exchanged and if the challenge is authenticated, the BMS-K(P) will unlock the ignition (spark), fuel injection, fuel pump and starter motor.

The Transponder chip
The “chip” in the Key does not contain a battery.  In stead it is powered by the magnetic field of the Ring antenna, which also acts as the RF communication medium.  In essence the transponder is a wireless read/write EEPROM with a unique serial number.

The Ring antenna and evaluation electronics
The Ring antenna both powers and communicates with the Transponder chip in the Key. The max communication distance between Key transponder and the Ring antenna is just short of an inch (2cm) and that is the reason why there should NEVER be any other Keys with transponders in close proximity as they would both be powered by the Ring antenna’s magnetic field and both try to communicate, thus essentially corrupting each others signals.

The Evaluation electronics
This is integrated in the Antenna ring unit and conditions both the RF and data signals to the BMS-K(P) in order to communicate with each other (read: rf <-> digital conversion). The Evaluation electronics is powered by Ignition (Terminal 15), and has the following pin-outs: 
pin1 : Terminal 15 (ignition)
pin2 : Terminal 31 (ground)
pin3 : data
pin4 : data

The BMS-K(P) ECU
A certain portion of the BMS-K(P) software is dedicated to the EWS.  This block of software integrates the data from the Key (by means of the Evaluations electronics, to the rest of the engine management functions of the ECU. It’s primary tasks are:

• To retrieve the identification data from the Transponder in the key and validate its authenticity
• To release the rest of the engine management functions, if the they key is authenticated
• It manages up to a total of 10 keys
• It manages the keys that have been blocked (typically if you’ve lost a key, you can have it blocked)

The EWS procedure at start-up is as follows:

• When the ignition is switched on, it powers the Evaluation electronics and in turn the Transponder chip in the Key
• The BMS-K(P) authenticates the key data against its corresponding data within the BMS-K(P)
• Based on a secret algorithm, a random number is manipulated by both the Transponder as well as the BMS-K(P). The Key’s answer is transmitted back to the BMS-K(P), and if they are a match, the rest of the engine management functions are released.

The dreaded “EWS issue” has a silver lining?

What to do when things go wrong
Unlike, loosing your key (quite probable) or an electronic failure within the BMS-K(P) (highly unlikely – cars have been using these modules for years!), the unreliability of the Ring antenna and Evaluation electronics, does have a silver lining… Anyone can replace it! (no special matching by the BMW diagnostic computer required) – unlike the learning of a new key or the replacement of a BMS-K(P) control unit!

That’s why you should have at least ONE spare unit amongst your riding party… AND ALWAYS carry your spare key… The spare key is essential as it is required when your loose (misplace, of course) your current key, however also required for the emergency Ring Antenna replacement procedure (the original ring antenna is difficult to replace, hence you will only be unplugging the wires from the original connector and plugging them into your replacement unit. However your replacement unit will not reach your key in your ignition switch – hence you require two keys… one in the ignition switch (to turn the ignition) and the other taped or cable-tied into the replacement ring antenna, to authenticate and enable your engine controller…)

What you require…

• A spare ring antenna (New part#:  61 35 7 705 247 ) released 06 2008
• Your spare ignition key!
• Some cable ties and/or tape (to fasten the spare key to the replacement ring antenna)

(Comment: AndyW) Alternative instructions below
WARNING: This is probably obvious but I’ll say anyway for my peace of mind! If you carry a spare EWS / Ring Atenna and or spare key, should you loose them the security of your motorcycle / someone else’s motorcycle could be compromised!!

(Comment: Rob Llewelyn )
“You say that you need to carry a spare key on the bike to be able to do the workaraound if you carry a spare antenna. You say that this presents a security problem as anyone stealing the bike then has a valid key for the bike. The spare key that you store on the bike doesn’t need to be chipped as it only needs to work the old switch with your normal chipped key sitting in the new antenna. If you point this out, it makes it cheaper to carry a none chipped spare on the bike and is more secure. Hope this helps. Rob”

Is the ring antenna always at fault!
NO!  On some occasions the symptoms of the motor not starting and “EWS” displayed intermittently or permanently on the instrument cluster are NOT the result of a faulty Ring antenna!

If the Low beam comes on and “EWS” is displayed, when the ignition is switched on the first time after the battery has been removed, the Ring antenna is NOT faulty!

This happens when the BMS-K(P) boots up incorrectly… A good booted BMS-K(P) always shows the gear indicator in the instrument panel, provided the gear selector potentiometer is NOT faulty (GS-911 will tell you this).

Once the ignition is switched on a second time, the EWS should function normally!

(Comment: AndyW) Additionally some riders have reported issues with radio signal interferance e.g. mobile phone transmitters, wireless security systems etc (petrol stations are a common place temporary problems occur). Push your bike away from its current location and hey presto all is well again.

What to check before replacing the Ring antenna?

• Cycle the ignition again, and if the problem persists, then
• Check the wiring and wiring connector to the Ring antenna for:
  • Any damage (possibly caused by chaffing etc. or rodent damage)
  • Over tightened cable ties that might have cut into the wiring or are preventing good contact at the connector (due to lack of slack in the wiring)
  • Poor connection at the connector to the ring antenna
• Read the fault codes with GS-911. The ring antenna might not be the problem that is preventing your motor from starting!

Alternative Failed / Faulty EWS Ring Antenna work-around
you will not have to remove the top yoke or ignition lock in order to get you home or finish your trip.

1. On the back of the ignition lock there are two small torx screws that hold the ignition wiring security cover on. Remove these and you will then be able to see the wiring that plugs into the ring antenna.

2. Unplug this wiring from the RA (the plug has a small tab that you will need to ease out of the way to get it out)

3. Plug in the new RA

4. This is where you have to be a bit careful. If you only have the one key you have to put the key in the ignition then position the new RA over the key whilst turning the ignition on. the RA has to be able to read the chip in the key for it to work. Then start the bike. Once it is running you can remove the RA as it is only used to immoblise the starting system. If you have the spare key you can tape it inside the new RA and you then don’t have to worry about it being any where near the ignition lock. In this case just use the ignition key as normal as the chip is being read from the spare key. If you are going to leave it connected just make sure that you secure the new RA so it can not get damaged or foul the steering operation.

You wil only ever need one spare ring antenna as they are not coded to the bike so if you have more than one bike go down the same spare one can be used to start as many bikes as required.