Engine Controls - CAN/Byteflight Bus Diagnostics
SI B61 03 03General Electrical Systems
January 2006
Technical Service
This Service Information bulletin supersedes S.I. B61 03 03 dated June 2005.
[NEW] designates changes to this revision
SUBJECT
CAN/Byteflight Bus Diagnostics
MODEL
E60, [NEW]E61 (5 Series)
E63, E64 (6 Series)
E65, E66 (7 Series)
E90, [NEW]E91 (3 Series)
SITUATION
Introduced on DISPlus/GT1 with DIS CD32.0, a Bus Analysis tool is available to aid the diagnosis of CAN (Controller Area Network) and Byteflight Bus problems. Always use the latest DIS CD version in order to utilize the latest test plan.
INFORMATION
Introduction
In modern vehicles, components and control modules are networked by means of data buses. Data buses are capable of transmitting several messages and signals at any one time. The connected control modules only read those messages and signals that are of relevance to their operation.
If faults occur in this communication framework, fault memory entries are created in the control modules involved. Here, a distinction can normally be made between wire faults and logical faults, such as missing CAN messages. The fault causes shown can lead to bus faults.
If a data bus fails completely and permanently, the affected control units are no longer available for diagnosis. The fault is thus easy to locate.
However, it is problematic for diagnosis if a data bus only fails intermittently. In such cases, the stored fault memories of control modules do not point specifically to an intermittent failure of a particular data bus. The intermittent failure of a particular data bus can cause a number of different fault entries in several control modules.
[NEW] The test module "Bus analysis" (System analysis) in the Test Plan of the BMW Diagnostic System provides a path for diagnosis and is generated by the DIS automatically when Bus faults are stored in more than 1 control module. Bus diagnosis allows the cause for intermittent failure to be isolated down to the area of the data bus.
[NEW] The Bus diagnosis test does not diagnose MOST bus problems. Refer to SI B61 15 02 for MOST bus diagnosis. The test module can also be called up manually by selecting "Function Selection" button and then selecting "Complete vehicle/Body/Bus functions/Bus analysis/System analysis".
[NEW] The bus system analysis narrows down the cause of intermittently occurring faults in the area of the data buses and control modules.
[NEW] The results of bus system analysis state the possible causes of the faults as shown.
PROCEDURE
Bus diagnosis: procedures and messages.
It is very important before diagnosis begins that the fault memories are not cleared.
In the event of an intermittent failure of a data bus, many of different fault memory entries are possible. The fault memory entries in the different control modules can vary greatly.
The following is a step-by-step procedure for bus diagnosis, including the messages on the screen of the tester.
^ The diagnosis program will automatically select the "System Analysis" test plan "B6131_xxxxx", based on the stored faults, after a short test is performed.
^ If the diagnosis program does not automatically select the "System Analysis" test plan then troubleshoot other faults according to the DIS selected test plan.
1. Identification of engine type:
Bus diagnosis identifies the type of engine in a vehicle. The test module has to evaluate the fault memory entries differently based on the engine type. Make sure that the vehicle is identified automatically.
2. Read off all fault memories of all control modules:
^ Perform a "Short Test" on the entire vehicle using DIS CD 44 or higher.
^ Ensure that all the control modules can be identified.
^ [NEW] If more than 2 CAN faults or more than 2 Byteflight communication faults are stored, the "CAN/Byteflight" virtual module will be marked with an "X". An "X" will appear next to the "virtual" control module "CAN/Byteflight" or "CAN". Virtual means this is not a real control module but a wild card for all control modules on the CAN bus or Byteflight.
^ Page to the right after a "Short Test" is complete.
^ Highlight "System analysis B6131_xxxxx" test plan from the DIS test plan section and continue.
4. Evaluation of fault memory entries:
^ Once the test plan has been started, the following messages will be displayed:
"Evaluating fault codes stored in the system.
Time: approx. 30 seconds Please wait. Evaluation of quality of results:
*****Very High Quality
*Low Quality"
5. The determined causes of the fault:
Once the evaluation process is complete, the screen will display the following: (as an example)
"The determined causes of fault are as follows:
[1] **** DSC
[2] *** PT-CAN
[3] ** ARS
[4] End test module
The most probable cause of the fault is listed under
[1] Select test step"
^ Select [1] and continue.
6. Continue test plan:
^ The following messages are displayed (as an example) for this test plan.
"DSC
Dynamic stability control.
Analysis of the bus faults stored in the vehicle showed that the corresponding control module did not participate at least temporarily in bus communication".
^ Continue with test plan.
^ The messages shown are displayed (as an example) for this test plan.
"Possible causes of faults:
^ Voltage supply
^ Bus connection
^ Dynamic stability control
Check voltage supply and bus connection (branch lines, plug connections) for loose contacts. Replace control module if fault reoccurs".
^ Continue with test plan.
^ [NEW] The BMW diagnosis system proposes a separate test plan for each of the 3 most probable fault causes.
^ If problem was not found then use selection "[1] Return to selection", and continue in test plan.
^ If problem was found and repaired use selection "[2] End test module".
^ The fault memories can be displayed by selecting "Control Module Functions/CAN Byteflight/Read Info memory". The lists of faults that the system analysis looks at are displayed and can be selected for viewing.
7. [NEW] Inspection procedure for impedance measurement (PT-CAN, F-CAN, Local- CAN)
When directed by the DIS test plan or in cases where communication is lost on an entire bus system it may be necessary to measure the impedance of the complete bus circuit. When measuring impedance, it is necessary to disconnect the circuit being tested from the power supply beforehand. The vehicle's battery and battery charger should therefore be disconnected. Wait about three minutes to allow all capacitors in the system to discharge.
Inspection procedure for resistance test:
Impedance measurement with matching resistor PT-CAN, F-CAN, Local-CAN
On the Tester, switch to Measurement system -> Multimeter
Measurement function: Resistance
^ Measuring range: automatic
In order to prevent signal reflection, a 120 ohms resistor is fitted to two CAN bus nodes (at the extremities of the PT-CAN network). The two terminal resistors are connected in parallel and form a shunt impedance of 60 ohms. When the power supply is switched off the shunt impedance can be measured across the communication leads. In addition, the individual resistors can be tested independently of one another. (Tip for 60 ohms measurement: disconnect an easily accessible control module (not fitted with terminal resistor) from the bus and then measure the impedance between CAN Low and CAN High leads on the connector.)
Terminating resistor locations:
E65, E66 (PT-CAN)
1. One resistor located in the wiring harness at the front right spring strut dome.
2. One resistor is in the wiring harness under the back seat.
E60, E61, E63, E64
^ PT-CAN
1. One resistor is in the DSC (Dynamic Stability Control) module.
2. One resistor is in the SGM (Safety Gateway Module) up to 9/2005, or the KGM (Body Gateway Module) from 9/2005 production.
^ F-CAN
Vehicles with AFS (Active Front Steering)
1. One resistor is in the cumulative steering-angle sensor in the steering box.
2. One resistor is in the DSC sensor under the front passenger seat.
Vehicles without AFS
1. One resistor is in the DSC control module.
2. One resistor is in the DSC sensor 2 under the front passenger seat.
E90, E91
^ PT-CAN
1. One resistor is in the DSC (Dynamic Stability Control) module.
2. One resistor is in the EKP (Electric Fuel Pump).
^ F-CAN
1. One resistor is in the DSC (Dynamic Stability Control) module.
2. One resistor is in the SZL (Steering Column Switch Center).
8. [NEW] DC voltage measurement PT-CAN, F-CAN, Local-CAN
Precondition for the measurement: battery connected and ignition on!
On the Tester, switch to Measurement system -> Multimeter
^ Measurement function: Voltage
^ Measurement type: =
^ Measuring range: automatic
In order to establish whether the CAN Low or CAN High lead is defective, you can measure the CAN Low (CAN High) voltage to ground.
CAN Low to ground: voltage approx. 2.4 V
CAN High to ground: voltage approx. 2.6 V
These values are approximate values and can vary by a few hundred mV depending on the bus load.
9. [NEW] Oscilloscope measurement PT-CAN, F-CAN, Local-CAN
Precondition for the measurement: battery connected and ignition on!
On the Tester, switch to Measurement system -> Oscilloscope setting
^ Measurement type: =
^ Measuring range: =/- 5V
^ Frequency range: 1 kHz
In order to obtain a clear idea of whether the CAN bus is functioning properly, it is very useful to be able to observe activity on the bus. What is important here is not to analyze the actual data being transmitted, but simply to be able to see that the CAN bus is operating. The oscilloscope test can state that "the CAN bus is probably operating without faults"
If the oscilloscope is used to measure the voltage differential between the CAN Low and CAN High ground leads, a square wave signal with the voltage limits U (mm) = 1.5 V and U (max) - 2.5 V is obtained.
If the oscilloscope is used to measure the voltage differential between the CAN High and CAN Low ground leads, a square wave signal with the voltage limits U (mm) - 2.5 V and U (max) - 3.5 V is obtained.
These values are approximate values and can vary by a few hundred mV depending on the bus load.
10. [NEW] Resistance test K-CAN
No defined resistance test can be carried out at the K-CAN data bus, as the resistance varies depending on the internal switching logic of the control modules!
11. [NEW] Measuring K-CAN DC Voltage
Precondition for the measurement: battery connected and ignition on!
On the Tester, switch to Measurement system -> Multimeter
^ Measurement function: Voltage
^ Measurement type: =
^ Measuring range: =/- 10 V
In order to establish whether the CAN Low or CAN High lead is defective, you can measure the CAN Low (CAN High) voltage to ground.
CAN Low to ground: voltage approx. 4.8 V
CAN High to ground: voltage approx. 0.2 V
These values are approximate values and can vary by a few hundred mV depending on the bus load.
12. [NEW] Oscilloscope measurement K-CAN
Precondition for the measurement: battery connected and ignition on!
On the Tester, switch to Measurement system -> Oscilloscope setting
^ Measurement type: =
^ Measuring range: automatic
^ Frequency range: 1 kHz
In order to obtain a clear idea of whether the CAN bus is functioning properly, it is very useful to be able to observe activity on the bus.
What is important here is not to analyze the actual data being transmitted, but simply to be able to see that the CAN bus is operating. The oscilloscope test can state that "the CAN bus is probably operating without faults". If the oscilloscope is used to measure the voltage differential between the CAN Low and CAN High ground leads, a square wave signal with the voltage limits U (mm) = 1 V and U (max) = 5 V is obtained. If the oscilloscope is used to measure the voltage differential between the CAN High and CAN Low ground leads, a square wave signal with the voltage limits U (mm) = 0 V and U (max) = 4 V is obtained.
These values are approximate values and can vary by a few hundred mV depending on the bus load~.
13. [NEW] CAN bus without function
If the K-CAN or PT-CAN data bus indicate no function, it is likely that a short circuit has occurred on the CAN Low and/or CAN High lead, or that a control module is defective. In order to localize the cause of the fault, it makes sense to use the following procedure:
^ Disconnect one CAN-bus node after the other until the unit causing the fault (= control module x) is found
^ Check the lines to control module x for short circuits
^ If possible, check control module x
However, this procedure only leads to success if a tap line from a control module to the CAN bus has a short circuit. If a CAN bus lead itself has a short circuit, the wiring harness must be checked.
14. [NEW] Diagnosis information
Two different bus faults can be entered in the CAN bus control modules:
^ CAN communication fault
^ CAN wire fault
The communication fault provides an overview of the control modules that have failed on the CAN bus, i.e. were no longer able to communicate. The "CAN communication fault" can only be read out if the fault is currently not present. If the fault is currently present, it is no longer possible to communicate with the control module. This means that the fault memory cannot be read either! Physical wire fault can be detected by the use of fault-tolerant CAN transceivers. However, at the moment there are only fault-tolerant transceivers for the K-CAN data bus. This means that only control modules that are connected to the K-CAN data bus can have made the fault memory entry "CAN wire fault". The CAN transceiver is also unable to distinguish between the individual fault categories shown. If the bus fault "CAN wire fault" is entered in a control module, this can mean (Refer to the image above).
Break in wiring (single-wire operation): each control module contains a separate bus termination. This means that, even in the case of a break in wiring, the voltage level can be maintained across the entire K-CAN network. The consequence of this is that a transmitting control module does not detect this fault and continues to work in two-wire operation. However, if a control module transmits a message across the break, the receiving control module only detects activity on the undamaged bus line. The receiving control module thus detects single-wire operation and sets the fault "CAN wire fault". If different control modules receive messages across the break, a number of control modules can have made this fault memory entry in single-wire operation!
Short circuit: if there is a short circuit in the system, all K-CAN control modules must have entered the fault "CAN wire fault". In order to localize the short circuit, follow the procedure for "CAN bus without function".
Refer to SBT 61 02 03 (015) for further information, which can be accessed via TIS.
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