Specifications

46
Testing Testing Bus Systems
NOTE:
i Note the following regarding bus system voltage:
• Buses operating at 12V usually have a 7V minimum operating voltage.
• Voltages are checked using a breakout box or backprobing at the control module.
M Bus (Motor Bus)
The M Bus (motor bus) is for IHKA Stepper motor operation. It is used exclusively between the
climate control module (IHKA/IHKR) and a set of stepper motors controlling air distribution. Each
stepper motor is on the M Bus and transmits and receive data on a single wire. The M Bus
consists of a three-wire ribbon which is separate from the vehicle wiring harness.
The M Bus has the following characteristics:
• Active anytime the ignition is on.
• Each stepper motor is connected in parallel to the IHK module via a three-wire ribbon (power,
ground, and signal).
• The IHK module provides the 5V bus voltage (Master Controller).
• A 2.5V (average voltage) reading indicates that communication is occurring.
• Constant communication occurs until the GM sends a sleep command over the K Bus.
• Communicates at 650 microseconds with an average period of 50 microseconds.
NOTE:
i For an operational check on the M Bus for 540/740/X5 models using the High Instrument Cluster
system (digital display message center), see “To check M, I, and K Bus operation:” on page 49.
Table 4-18 2002 and later bus system applications, part 2
Model Most
Byte
Flight
Pt CAN Lo CAN BSD Lin F CAN K CAN
E65/66 YES YES YES YES YES
E60
5Series
YES YES YES YES YES YES YES
E85 Z4 YES YES
E46
YES (2003
and later)
Table 4-19 Bus system specifications
Specification M K P I D
CAN
High
CAN
Low
Baud Rate N/A 9.6 kb/s 9.6 kb/s 9.6 kb/s 10.4 kb/s 500 kb/s 500 kb/s
Supply Voltage 2.5–5 V 12V 12V 12V 12V 2.5–5V 0–2.5V
Minimum Operating
Voltage
7V 7V 7V 7V 10.5V 10.5V
Voltage Source
IHK GM GM
LCM/
LSZ
each
module
each module
Wake-up Signal
Commanded By
EWS or IKE