- A CAN timeout fault code is set due to the absence of a CAN input signal.The cause of this may be not only the transmitter control unit, but
also the CAN networking.
- For example:No CAN message was received from control unit A.
Bus OFF fault
- A Bus OFF fault code is set, when the control unit cannot send a certain amount of messages to the CAN bus or the messages are
incomplete.The control unit then switches off for a short time from CAN bus.
- For example:CAN controller: CAN bus OFF
Functional CAN fault
- A functional CAN fault code is set because of an implausible CAN input signal.The cause of this is not the CAN networking, but the
transmitter control unit or its sensors.
- For example:CAN signal 'A' from control unit B is implausible.
Notes on CAN faults that cannot be read out as fault codes.Bus wake-up event
- An event that wakes up the bus without reason is designated a bus wake-up event.
- The cause of this is not the CAN networking, but the transmitter control unit or its sensors.
- Further possible causes of fault:
- Magnetic fields caused by nearby high-voltage installations, railroad installations or power plants.
- Magnetic fields can radiate on to lines and control units in rare cases and cause undefined behavior in the control units.
- The special tool 'Star Diagnosis CANtool' can be used to log bus wake-up events, bus keepawake events and other signals.
Bus keepawake event
- When a control unit keeps communication on the bus awake without reason, this is designated a bus keepawake event.
- The cause of this is not the CAN networking, but the transmitter control unit or its sensors.
- Further possible causes of fault:
- Magnetic fields caused by nearby high-voltage installations, railroad installations or power plants.
- Magnetic fields can radiate on to lines and control units in rare cases and cause undefined behavior in the control units.
- The special tool 'Star Diagnosis CANtool' can be used to log bus wake-up events, bus keepawake events and other signals.
2.1.1.2. No further information available.
2.1.1.3. General CAN fundamentals
Test 2.1.1.3.1: High-Speed CAN (125 kBit/s , 500 kBit/s)
Test 2.1.1.3.2: Low-Speed CAN (83,3 kBit/s)
2.1.1.3.1. High-Speed CAN (125 kBit/s , 500 kBit/s)
General CAN fundamentals
High-Speed CAN (125 kBit/s , 500 kBit/s)
- 125 kBit/s : Interior CAN busSeries 221
- 125 kBit/s : Telematic CAN busSeries 221
- 500 kBit/s : For example:Drive train CAN bus
- 500 kBit/s : For example:Diagnostic CAN-Bus
- This CAN bus does not permit single-wire mode.
- This means that both CAN lines are always required for fault-free communication between the control units.
- This CAN bus requires external terminating resistors.
- The terminating resistors can be located in control units or voltage distributors depending on the CAN bus.
Legend and description for figure 1CAN-H: CAN bus HighCAN-L: CAN bus LowECU 1 ... n: Control unit 1 ... nCAN terminating resistor (
Example: 120ohms)Legend and description for figure 2U 1: Specification approx. 3,6 voltsU 2: Specification approx. 2,5 voltsU 3: Specification
approx. 1,4 voltsContinue with button F2
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