Two wire K-CAN Bus systems (Body Bus), connecting several control modules, sensors and actuators, became the norm in BMW vehicles beginning with the 2002 model year. The K-CAN, a 2-wire bus, connects the instrument cluster, climate control (IHKA), airbags (SRS), lighting system and tire pressure control. A failure in the K-CAN may cause malfunctions in the warnings lights or control modules for any of those system.
The vehicle may exhibit one or more of the following problems:
- Random instrument cluster warning light failures.
- Instruments cluster inoperative.
- Climate control, airbags, lights or tire pressure sensors inoperative.
To start with, use the Autologic scan-tool to check for fault codes:
- Fault code E204 K-CAN line faulty.
- Fault code E247 K-CANline Low fault.
- Fault code D904 K-CANline High fault.
- Fault code E5C4 K-CAN communication fault
NOTE: The best tool for checking bus systems is an oscilloscope.
Check for any obvious issues like to water damage to control units logging K-CAN faults. Also check connectors and splices for water corrosion.
Disconnect individual K-CAN modules one at a time. If communication to other modules resumes, the disconnected module is the faulty one.
Disconnect all modules successively (except the Gateway and CAS – will need to be swapped from another vehicle). If you still have no communication on K-CAN, test the wiring harness for short to B+ or B-.
If the preceding fault codes are found, investigate the following causes and repair as necessary:
- Failure of a body module: climate control, airbags, lighting or tire pressure control.
- Water damage to a module or electrical connector.
- Damage to wiring or short in wiring.