Fault-Tracing Information
Controller area network (CAN) fault-tracing
General information
The diagnostic trouble code is stored when communication between Central electronic module (CEM) and relevant control module has been interrupted. There can be a number of causes for interruptions in the communication:
- Central electronic module (CEM) has stopped sending the signal that receiving control module (the control module that generated this fault code) expects.
- Intermittent open-circuit in one or both CAN cables in part of the network
- Intermittent short-circuits between the CAN cables
- Intermittent short-circuits between one of the CAN cables and ground or supply voltage
- Incorrect signal configuration in control module that set diagnostic trouble code. The problem may be due to a control module having been replaced without downloading new software when replacing.
Note! If there is a diagnostic trouble code (DTC) for a communication fault in a control module, check whether diagnostic trouble codes (DTCs) have been stored in the central electronic module (CEM). Central electronic module (CEM) monitors the voltage level on the CAN-lines, and is the only control module that directly can set a diagnostic trouble code for short-circuiting to ground or to voltage for any of the leads. Central electronic module (CEM) shall not be replaced in case of CAN-fault, unless troubleshooting reveals that the module has an internal fault.
Corrective actions
1. If trouble codes that indicate lost communication on CAN are generated in several control modules, first troubleshoot the trouble codes in the central electronic module (CEM).
2. If the problem is intermittent, erase the diagnostic trouble code and check that it is not generated again.
3. If trouble codes that indicate lost communication on CAN only have been generated in the control module that has generated this trouble code, try to solve the problem by downloading new software to the control module.
4. Check the cables in CAN according to the following troubleshooting.
Other information
- General information about fault-tracing in CAN Initial Inspection and Diagnostic Overview
- Go to the tab software and program the control module with the latest software.
- See Design and Function, CAN.
Continue - Verification
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Verification
- Ignition on
- Wait for 20 seconds.
Note! This first verification assumes that download of new software was required in the control module that generated the diagnostic trouble code. If download of new software was not required: read out diagnostic trouble codes and check if the code status is permanent or intermittent to learn how difficult it will be to find the fault.
Read out the diagnostic trouble codes in the vehicle.
Check that the diagnostic trouble code (DTC) for faulty communication is not stored again.
Has the fault been remedied?
Yes - FAULT FOUND
No - Measuring cables in HS-CAN
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Measuring cables in HS-CAN
- Ignition off
- Disconnect the battery negative lead.
- Remove the central electronic module (CEM)
- Connect the breakout box to the cable harness for the central electronic module (CEM). Do not connect the central electronic module (CEM).
Hint: Where a breakout box cannot be used, take readings from the rear of the affected connectors if possible. This prevents terminal pins and socket housings being damaged.
Disconnect CAN to make it easier to locate a fault. A suitable point to part CAN is at central electronic module (CEM) and that is why this troubleshooting starts from central electronic module (CEM).
Take resistance readings across the following terminals. Various readings will be obtained due to the structure of the network. Twist the cable harness and work the connectors at accessible points along the cable harness in order to check whether the resistance changes during each measurement. This method can be used to detect intermittent short-circuits or open-circuits.
Note! The following resistance readings only refer to the main lines in HS-CAN, not the junctions that exist for some control modules. See the Wiring diagram Service Manual for the relevant car model. If an open circuit or short-circuit on one of these junctions is suspected, the connector at the control module on this junction must be unplugged and the measurement done at that point.
Remedy as necessary.
Take the following readings
- For vehicles with structure week -200945:
1. Resistance between C3:47 and C3:48. Resistance should be 120 ohms.
Note! The measuring value will only be 120 ohms if the main line in CAN is intact. If there is a short-circuit in CAN, either in the main line or in a junction, the resistance will be 0 ohms.
2. The resistance between C3:48 and a connection to voltage as well as between C3:48 and a short-circuit to ground. The resistance shall be very high (more than 1 Mohms).
3. The resistance between C3:47 and a connection to voltage as well as between C3:47 and a short-circuit to ground. The resistance shall be very high (more than 1 Mohms).
- For vehicles with structure week 200946- :
1. Resistance between C3:6 and C3:7. Resistance should be 120 ohms.
Note! The measuring value will only be 120 ohms if the main line in CAN is intact. If there is a short-circuit in CAN, either in the main line or in a junction, the resistance will be 0 ohms.
2. The resistance between C3:7 and a connection to voltage as well as between C3:7 and a short-circuit to ground. The resistance shall be very high (more than 1 Mohms).
3. The resistance between C3:6 and a connection to voltage as well as between C3:6 and a short-circuit to ground. The resistance shall be very high (more than 1 Mohms).
Hint: Any short-circuiting that has been measured on CAN may be either on the main line or any of the junctions. If a fault is found, try to disconnect the junction with the fault at a point further forward. Try to locate the fault in this way.
Other information
- Battery, disconnecting Battery, Disconnecting
- Connecting the breakout box Connecting The Breakout Box. Central Electronic Module (CEM)
- Checking wiring and terminals Checking Wiring And Terminals
- See Design and Function, CAN.
Was a fault detected?
Yes - Verification
No - Checking the traffic load on the CAN cables
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Checking the traffic load on the CAN cables
- Connect the central electronic module (CEM) to the breakout box
- Connect the battery.
- Ignition on
Note! When the adapter cable harness and the central electronic module (CEM) have been connected, there is access to both sides of CAN (MS-CAN and HS-CAN). There will also be traffic on both networks. Be careful to check the terminals between which the readings are to be taken so that the intended reading is not taken on the wrong network.
Faults in CAN may be due to a control module sending faulty messages that interfere with the ordinary communication. Incorrect sending of messages result in significantly increased traffic on CAN. The load can be checked by reading the average value of the voltage on the CAN cables in relation to ground.
Check as follows:
- For vehicles with structure week -200945:
1. Measure the voltage between C3:48 and ground. The voltage shall be approx. 2.3 V.
2. Measure the voltage between C3:47 and ground. The voltage shall be approx. 2.8 V.
- For vehicles with structure week 200946- :
1. Measure the voltage between C3:7 and ground. The voltage shall be approx. 2.3 V.
2. Measure the voltage between C3:6 and ground. The voltage shall be approx. 2.8 V.
Other information
- Connecting the breakout box Connecting The Breakout Box. Central Electronic Module (CEM)
- Battery, disconnecting Battery, Disconnecting
- See Design and Function, CAN.
Is the value OK?
Yes - Fault-tracing without result
No - Identifying a control module in CAN
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Identifying a control module in CAN
If the load on CAN is too high it may be due to a control module, a so-called "interfering control module", sending incorrect messages on CAN. The fault may also be due to an intermittent short-circuit to supply voltage or ground in one of the CAN cables. This results in the control modules on CAN starting to send error messages. The fault may occur without any of the control modules storing a diagnostic trouble code (DTC). To check the load on CAN, the voltage between the CAN-lines can be measured.
Note! It is not necessarily the control module that has set the diagnostic trouble code that communicates incorrectly. Incorrect messages may come from any control module on the same part of CAN. However, faulty communication in one network cannot affect the communication on the other network. In other words, faulty communication on MS-CAN cannot disrupt communication on HS-CAN and vice versa.
Take the following readings
- For vehicles with structure week -200945:
Check load on HS-CAN by measuring voltage between C3:48 and C3:47. The voltage's average value shall be approx. 0.5 V (permitted is 0.4 to 0.6 V). In case of communication error, the voltage is approx. 0.7 V and higher.
- For vehicles with structure week 200946- :
Check load on HS-CAN by measuring voltage between C3:7 and C3:6. The voltage's average value shall be approx. 0.5 V (permitted is 0.4 to 0.6 V). In case of communication error, the voltage is approx. 0.7 V and higher.
In order to identify which control module is communicating incorrectly, cut the power supply to one control module at a time. Check the voltage in the CAN cables again. The easiest way to cut the power supply is to remove the fuse(s) for the relevant control module. Continue until the voltage between the CAN cables drops to approximately 0.5 V.
Hint: When the suspected control module has been identified, connect and disconnect the supply voltage to the control module a number of times to verify that the fault appears and disappears. Ignition off between each check.
Note! Do not cut the power to the central electronic module (CEM) unless it is the last control module left to check.
The control module that is communicating incorrectly must be replaced.
Note! A faulty control module that disrupts communication can place other control modules in Limp-Home mode (i.e. they work but with limited functionality) even after switching the ignition off and on a number of times. To remedy this, disconnect and reconnect the battery negative terminal to restore the control modules to normal function.
Remedy as necessary.
Continue - Verification
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Verification
Hint: Once a fault has been repaired, conduct a verification to check that the fault has been remedied.
- Reinstall the connectors, components etc.
- Ignition on
- Erase diagnostic trouble codes (DTCs) in all control modules
- Start the vehicle. Allow the vehicle to run for 10 minutes.
Read out the diagnostic trouble codes in the vehicle.
Is the diagnostic trouble code for configuration fault regenerated?
No - FAULT FOUND
Yes - Information
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Fault-tracing information
Information
Fault-tracing information
The fault should have been detected and remedied. As this is not the case fault-tracing has failed.
Exit fault-tracing for this diagnostic trouble code (DTC) or make another attempt.
Do you want to exit fault-tracing?
Yes - Exit fault-tracing
No - Attempt New Test
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Attempt New Test - General information
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Fault-tracing without result
Information
Fault-tracing information
Verification shows that the fault is no longer present. The diagnostic trouble code (DTC) was probably caused by an intermittent fault.
Fault-tracing for this diagnostic trouble code (DTC) is not followed by a verification.
You can view the information again or exit fault-tracing for this diagnostic trouble code (DTC).
Do you want to view information again?
Yes - Attempt New Test
No - No Fault Found
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No Fault Found - DONE
Attempt New Test - General information
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Information
In exceptions the fault code can be generated as a result of a damaged control module. However, do not replace control module, unless complete troubleshooting has been performed according to all earlier steps in the troubleshooting, and no other faults have been confirmed. Also, do not replace control module if the fault is intermittent.
Has the fault been remedied?
Yes - FAULT FOUND
No - Fault-tracing information
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