I/K Bus Topology

MRS III EWS 3.3 RDW

4
HIGH
80 3
60 120 140
100
2
1/min
x 1000
5
INSTRUMENT
IHKA
100 160
80 180
40 60 200 120 6
220
1
CLUSTER
40
½ 20
240

0 20 140 0 7
km/h
MPH 40 0
ELECTRONIC 20 15 10
70 0 F 640 F !

123456
miles
122 4 +72 0F PRND S P ! ABS

CHECK OIL SERVICE

AUTO REST - +
A

K-BUS K-BUS
ENGINE INSPECTION 20 DIGIT READOUT 432
DIAGNOSIS BUS

I-BUS
M-BUS

SZM LWR BMBT

INFO
1 4 MENU
On-board computer GPS-Navigation

Antenna
2 5

CAN BUS
DSP Aux. Ventilation
3 6 TONE SELECT

Amplifier
Code
FM AM

M FZV DWA
Emergency

GM III MODE Set

11.13.2000 Thursday
Monitor off

10:17
MENU

P-BUS
MK 3 NAV MFL
M B
M

W
SRS
AIRBAG
POWER
GPS NAVIGATION SYSTEM

Driver's Door
Switchblock/ Passenger's
M Module Door Module
RADIO
PM-BT LEW
PM-FT/SB LCM
M CHECK
ENGINE

Seat Memory Sunroof CMT 7000

Module Module
DSP
interface box
PM-SM PM-SHD DSC III

CDC PDC
AGS
obd ii STANDARDIZED
FAULT CODES

r
ne
an
Y

Sc
1 2 3 4

DME
N

OBD II
CONNECTOR
TXD II
DIS
BMW

{ DIAGNOSIS BUS
BMW DIS

CHECK
ENGINE
20 PIN TXD
DIAGNOSTIC
BMW DIS

CONNECTOR Example:
up to 9/00
E39 High Version with I and K
bus network.

KOMBI
RAIN DIAGNOSIS BUS (TXD)
EW
S3

80 3 4
SENSOR
.3

60 100 1/min 5
100
120 140
160
2 x 1000
80 180
40 60 200 120 6
AIC 0
½
20
40
20
220
240

140
1
0 7
km/h
MPH 40 0

DSC III
ELECTRONIC 20 15 10
!
HC

MR 012345 km 1224
miles
PRND S321 P ! ABS
SO
B

S3 CHECK MP
MP + 88 8 L/100 KM/H
KM/L
OIL SERVICE INSPECTION
!

K-BUS
ENGINE

K-BUS
K-BUS

RADIO CAN BUS

IHKA RECEIVER
MODULE
- BASS +

- TREBLE +
DOLBY SYSTEM FLAT
FADER

BALANCE

70 0 F 640 F
AUTO
FBZV GM III DWA B
M
W

0 0:
WH
228
390
AUDIO
A m
14
1 7 0 0:W
3W H

IHKA
MB

TEL
AUTO REST - +
BC SRS
AIRBAG
P-BUS

K-BUS MIDK-BUS DIAGNOSIS BUS

M-BUS

B MFL-CM
M

Telephone
Driver's Door Psgr's Door Interface Box
Switchblock/ Switchblock/
M-BUS

K-BUS

Module Module DME AGS

M FBZV GM III
PM-FT/SB
DWA
PM-FT/SB LCM III
GR II
P-BUS

RADIO
StarTAC

M
BMW

Seat Memory Sunroof AMPLIFIER

Module Module
PM-SM
Driver's Door PM-SHD SRS
AIRBAG

M Switchblock/ Passenger's MID PDC

Module Door Module MFL-CM
M PM-FT/SB
PM-BT

Seat Memory Sunroof

Module AMPLIFIER
obd ii STANDARDIZED
Module
LCM
LWR

FAULT CODES

PM-SM 1 2

Sc
an
3

ne
r
4 Y
PM-SHD ABS/ASC5
N
OBD II - DLC
(diagnostic link connector)
EHC

TXD II
AGS
CAN BUS

BMW
DIS
obd ii STANDARDIZED
FAULT CODES
{ DIAGNOSIS BUS
BMW DIS

n er
an
Sc
1 2 3 4

TXD
20 PIN
DIAGNOSTIC Example: DME
CONNECTOR
E53 Base Cluster with K bus
BMW DIS

network .
iC
oD
M

DIAGNOSIS BUS
18
Bus System Troubleshooting
EWS II MRS
The I/K bus consists of a single copper wire. The wire color of the I and K bus is uniform
throughout the vehicle with: I-bus WS/GR/GE and the K-bus WS/RT/GE (Note: 2001 E39s
with base Kombi have changed K-bus wire color to the same as the I-bus, WS/GR/GE).

Due to the linear structure of the network, the I/K bus is available for other modules in the
event of a disconnected or failed control unit. Just as the CAN bus, this is referred to as a
“Tree” structure with each control unit occupying a branch. The I/K-bus provides the diag-
nostic connection to the control units located on those busses (except IKE/KOMBI).

Always refer to the ETM to determine the exact wiring configuration and color for a specific model.

Troubleshooting the I/K bus

The failure of communication on the I/K bus can be caused by several sources:

• Failure of the bus cable.

• Failure of one of the control units attached to the bus.
• Failure of the voltage supply to individual modules.
• Interference in the bus cables.

The I/K bus is active when KL R is switched on, it remains active until 60 seconds after the
last message. If the key is switched off (KL30) the bus may be activated for a time by indi-
vidual users via a “wake-up” message.
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Unlike the CAN bus where each control unit BMW Test system Multimeter

(subscriber) provides voltage for communica-

Freeze image

tion, the I/K-busses use only determined 10.15 V DC Minimum

Master or Stand-by Controllers to supply

Maximum

B+for communication. The voltage level on the

20 0 20
System voltage
Measurement Voltage Resistance Temperature Rotation speed
Function V Ohm o
C

I/K bus must be above 7V. The nominal value Current

2A
Current
50A
Current
1000A
Diode test
-|>|-
Pressure
bar 2nd

should be close to the system voltage of the

measurement

Measurement MFK 1 MFK 2 Current probe Pressure Temperature

Connection Sensor Sensor

vehicle. Measurement
Kind = Effective value

automatic ± 500 mV Stimulate

Just like the CAN bus, the fact that voltage is

Measurement
Range

Multimeter Counter Oscilloscope Stimulators Preset

present does not mean that the bus is fault setting measurements

free, it just means that the voltage level is suffi-

cient to support communication.

19
Bus System Troubleshooting
Control units that provide operating voltage to the I/K bus are:

On E38 and E39/E53 High version vehicles:

• The LCM is the Master Controller of the I-bus. The IKE and MID/BMBT are Stand-by
Controllers.

• The GM is the Master Controller of the K-bus.

On E46, E52 and E39/E53 Base version vehicles:

• The GM is the Master Controller for vehicles equipped with only the K-bus.

• The LCM/LSZ is the Stand-by Controller.

Failure of the Bus cable

The following faults can occur to the I/K bus wiring:

• Short Circuit to B+
• Short Circuit to B-
• Bus line down (open)
• Defective plug connections (damaged, corroded, or improperly crimped)

Short Circuit to B+: Modules that send a message see that the message was not
received and that the bus remains high. However, subscribers are unable to decide
whether the fault is due to a shorted line or a defect in the communication interface. The
module will repeat its message 5 times before discontinuing and faulting. The module will
continue to operate as normal minus any commands that could not be delivered by the
bus.

Short Circuit to B-: The subscribers do not interpret a low bus line as a fault but just as
a bus line deactivation. The Master and Standby controllers do detect the short and enter
it as a bus fault. (No communication).

Bus Line Down: The bus line may be open at any of several locations. As long as the
Master or Stand-by is still connected, communication can occur with any modules still
remaining. The fault situation will be the same as if the disconnected modules were defec-
tive themselves.

Checking the bus line is carried out just like any other wiring. Perform continuity tests
between the connections of different modules (all modules disconnected) without forgetting
to make sure that the bus has not shorted to ground or another wire. It is recommend-
ed to use the “Wire Test” in “Preset Measurements” which is more sensitive than
just a resistance check.

20
Bus System Troubleshooting
If Voltage level and the wire test are O.K then looking at the communication signal may be
useful. In order to get a signal, operate different devices on the I/K bus (e.g. MID/MFL) to
stimulate conversations.

The following are some examples of scope patterns that may be observed when checking
the I/K bus.
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BMW Measuring system Oscilloscope display

A [V]
Cursor 1 Memory Cursor 2
8 [V] V
Freeze Image
V High
Channel B 7V to B+
16 16 8 T
r Zoom
12 12 6
i
8 8 4 g
g
Amplitude
Channel A
V Low
4 4 2
e 0V to 2V
0 0 0 r
Amplitude
Channel B
-4 -4 -2
l
-8 -8 e-4
Time value
-12 -12 -6
v

-16
e
-16 -8 l Message Time
5ms to 30ms
-2.0 -1.0 0.0 1.0 2.0
-1.5 -0.5 0.5 1.5
ms Stimulate

Multimeter Counter Oscilloscope Stimulators Preset

setting measurments

61400100

Example of correctly operating I/K bus during communication

Correct communication on the I/K bus occurs in sporadic bursts with periods of
steady voltage around 12V.
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BMW Measuring system Oscilloscope display BMW Measuring system Oscilloscope display
Freeze Image Freeze Image
Cursor 1 Memory Cursor 2 Cursor 1 Memory Cursor 2
A [V] 8 [V] V A [V] 8 [V] V
Channel B Channel B

16 8 T 16 16 8 T
16
r r Zoom
12 12 6 Zoom 12 12 6
i i
8 8 4 g 8 8 4 g
Amplitude Amplitude
g Channel A
4 2
g Channel A
4 4 2 4
e e
0 0 0 r 0 0 0 r
Amplitude Amplitude
Channel B
-4 -4 -2 Channel B -4 -4 -2
l l
-8 -8 -4 e -8 -8 -4 e
Time value Time value
v -12 -6
v
-12 -12 -6 -12
e e
-16 -16 -8 l -16 -16 -8 l

-2.0 -1.0 0.0 1.0 2.0 -2.0 -1.0 0.0 1.0 2.0
ms -1.5 -0.5 0.5 1.5
ms Stimulate
-1.5 -0.5 0.5 1.5 Stimulate

Multimeter Counter Oscilloscope Stimulators Preset Multimeter Counter Oscilloscope Stimulators Preset
setting measurments setting measurments

61400100 61400100

Flat line at 12 volts Flat line at 5 volts

No communication is currently taking No output voltage from the Master or
place. The bus may be temporarily offline Standby controllers. Bus line may be
or shorted to B+. open or control unit may be defective.

21
Bus System Troubleshooting
Failure of one of the control units attached to the I/K bus.
Each control unit connected to the bus has an integrated communication module that
makes it possible for that control unit to exchange information. Failure of a control unit nor-
mally triggers a fault code in the other control units connected to the bus.

As a quick check for the I/K-bus, activate the four way flashers. The flash indicators must
light up in the instrument cluster. Switch on the Radio, and adjust volume using the MFL
or MID/BMBT, the volume must change accordingly.

On High version vehicles press the recirculation button on the MFL, The IHKA should
respond to the request. This test checks the gateway link as well as the the I and K bus
communication.

If the tests prove O.K, this means that communication on the bus is O.K. Any faults still
existing can only be related to faults specific to a control unit or a local I/K-bus wiring defect
to a module.

There are instances where failures may be software related. A faulted module may para-
lyze or take down the entire bus. This scenario would be evident by functions not being
carried out and and possible faults stored.

In order to isolate the defective control unit, the control units can be disconnected one at a
time. Repeat the bus test after each disconnected control unit. If the disconnected con-
trol module is the defective one the faults will only point to communication with that inter-
rupted module and no one else.

Once the module has been replaced (observing current S.I.Bs) and coded, perform the I or
K bus Test Module in the Diagnosis Program to ensure that communication is O.K.

Failure of the voltage supply to individual modules.

A slowly dropping battery voltage on a vehicle with discharged battery can lead to sporadic
communication faults in various control units on the bus. The reason is that not all control
units will switch off communication at the same voltage level leaving some modules still try-
ing to communicate. Always verify a properly charged battery and charging system and
fuses before beginning troubleshooting on the bus. Also, do not forget to check for a prop-
er ground to a control unit, this may not allow the bus to see a signal low (0-2V)

Interference in the bus cables.

Interference will have a similar effect to shorting or disturbing the bus wiring. Excessive
interference created by a defective alternator or aftermarket devices such as cell phones or
amplifiers may induce a voltage into the bus line and disrupt communication. This type of
interruption may be intermittent and faults may only be stored in some modules and not in
others. These faults are often difficult to reproduce. Isolate any aftermarket wiring in the
vehicle and see if the fault returns.
22
Bus System Troubleshooting