BMW MOST Bus - Troubleshooting Guide [Vlad on MCA]

 Great guide to the BMW MOST Bus (Media Oriented Systems Transport), used in all BMWs with fibre-optic connectivity. It covers what it is and what it does, as well as troubleshooting a lot of associated problems with these complex systems. It is from Vlad at MCA.org and can be found here: 

https://mca.electricmura.ro/en/blog-bmw-most-troubleshoot/

BMW BUS System Troubleshooting

Interesting and highly informative BMW training manual on troubleshooting the BUS system fitted to cars built from the late '90s through the 2000s. Detailed guides on design, diagnosis and repair of the original BMW CAN-BUS systems.

https://drive.google.com/uc?export=download&id=1vIxKdCSqhcQqEKfE_VTRVw7PWJuP6rNE

BMW BUS SYSTEM TROUBLESHOOTING:

1. Introduction

2. Definitions

3. Controller Area Network (CAN bus):

• Introduction
• CAN bus topology
• Troubleshooting the CAN bus

4. Diagnosis Bus (D-bus):

• Introduction
• D-bus topology
• Troubleshooting the D-bus

5. Information and Body Bus:

• Introduction
• I/K bus topology
• Troubleshooting the I/K bus

6. Peripheral Bus (P-bus):

• Introduction
• P-bus topology
• Troubleshooting the P-bus

7. Motor Bus (M-bus):

• Introduction
• M-bus topology
• Troubleshooting the M-bus

8. Review Questions

All models using Bus System from model year 1991 onwards.

This module discusses:

• Advantages of using bus systems in a vehicle.
• Various bus systems used in most BMW vehicles.
• Operating principles of a serial bus.
• Methods of troubleshooting bus lines using the diagnosis program.
• Distinguishing a correctly operating bus line on an oscilloscope.

Have fun!

iDrive Safety Systems Disabled faults explained - Codes, Causes + Fixes.

It's a common event - you start up the BMW one day and suddenly get an iDrive warning saying there is a fault and all the airbags have been turned off. This now greets you every time you start up and both the airbag and seatbelt warning lights stay on the dash permanently, which is an MOT fail. Safety is paramount, so before you head towards a dealer and a huge bill take note that it is hardly ever a faulty part and is far more likely to be a false alarm thrown up by an overkill safety system!

This is an issue I have begun to encounter when working on my E60 530d, particularly when disturbing wiring inside the car and refitting trim, though most cases occur during day to day use and abuse of the interior. It applies to all iDrive equipped and LCI BMWs. The safety system, comprising the multiple airbags, seatbelt pre-tensioners and other devices are all linked into the CANBUS system and have sensors everywhere. If the slightest malfunction is detected anywhere in the safety system, the iDrive shuts it all down assuming that it has prevented a faulty airbag going off at random, when more often than not something has just happened to disturb a sensor for a split-second. There are sensors in the dash, doors, pillars, under the seats, even in the boot, so items getting jammed in places and maltreatment of the interior is the likely culprit. Sadly, once the iDrive warning is up then it's there to stay until reset using a trouble-code scanner. If you have access to one of these then life with this iDrive warning is a breeze - pretty much any one will do, even £20 eBay items like BMCables.com or ones that connect to your iPhone like iOBD. The system is so complex and temperamental that garages will replace expensive parts as a matter of course and there are multiple cases on Bimmer-Forums etc. where this hasn't fixed the fault and a simple workaround has, so if you don't have a scanner at least you can increase your chances of the warning being cancelled quickly and avoid getting ripped off if a trouble-code persists.


SFZ: Satellite Vehicle Centrum

9AFF - Resistance firing circuit safety battery terminal too high

• Low battery voltage: Has battery been allowed to run low? / Has a lot of diagnostics been done on the car recently? - Charge / replace battery.
• Battery has moved in boot: Ensure battery is bolted down and not going to move around. Check battery live terminal is secure, well on the stud and not twisted or jammed against something.
• Wire connector is loose: Check fitment of sensor wire connector next to battery live terminal. If apparently OK, wiggle wire connector, delete fault-code and see if it comes back - if not, secure wire connector with tape / cable-tie.
• Battery live-terminl under tension: Is red live wire to battery snagged and tugging on terminal / are any auxiliary wires connected to battery live-terminal - make sure wires to terminal are slack and have plenty of room / re-tighten the battery live-terminal at a better angle for the U-shaped live wire. [In my case the power lead to my aftermarket amplifier was trapped under the trim and was tugging on the live-terminal when something heavy was put on the boot floor.]

This is most common safety system fault and there is much discussion of it online. The cable / sensor is difficult / costly to replace, so if none of the above work there is a tried and tested bypass method, guides for which can be found here - http://5series.net/forums/diy-do-yourself-14/battery-safety-terminal-bypass-125288/.

Satellite B-Pillar Right:

• Has wiring under the steering-cowl been disturbed?

Satellite B-Pillar Left:

• Has wiring behind the glove-box / round the passenger fuse-box / in the passenger footwell.

There is no reason these sensors should fail without being damaged and will usually be a one-off fault and be easily cancelled with an OBD scanner.


Seat Pad Occupancy Sensors:

• Has the seat squab been impacted or had weight in one area? i.e people climbing on seats.

This is often a one-off fault code event from disturbed wires and will be quickly cancelled with a scanner, however the seat-pad sensor is prone to damage, especially from impact to the seat. This can be bypassed to avoid replacing parts, see here - http://www.ebay.co.uk/itm/Seat-Occupancy-Mat-Emulator-For-BMW-E90-E91-E60-E61-E87-E88-Airbag-Sensor-Bypass-/200967932097. 


Seatbelt Pre-tensioners:

98E2 Interruption detonation circuit (seat belt tensioner right)
9862 Interruption detonation circuit (seat belt tensioner left)

• Is something jammed under the seat?

This can be disturbed wires again and easily cancelled, but it can also be a broken seatbelt pre-tenioner, so to avoid the ludicrous cost of replacing these there are various bypass techniques for bypassing them, such as here - http://www.bimmerfest.com/forums/showthread.php?t=666775.