Fault-Tracing Information
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 fault can be due to a customer or workshop replacing a control module without downloading new software for the replacement.
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 there are diagnostic trouble codes stored in several control modules that indicate lost communication on the CAN-net, first try to troubleshoot diagnostic trouble codes in 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 there are only diagnostic trouble codes that indicate lost communication on the CAN-net stored in the control module that generated this trouble code, try to solve the problem by downloading new software to the control unit.
4. Check the cables in the CAN network according to the following fault-tracing
Other information
- General information about fault-tracing in the CAN network Initial Inspection and Diagnostic Overview
- Go to the tab software and program the control module with the latest software.
- See also Design and Function, CAN-network.
Continue - Verification
-------------------------------------------------
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 CAN network (MS-CAN)
-------------------------------------------------
Measuring cables in CAN network (MS-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 the CAN network to make it easier to locate a fault. A suitable point to disconnect the network is at the central electronic module (CEM). Fault-tracing therefore starts from the 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 during each measurement to identify any intermittent short-circuits.
Note! The following resistance readings only measure the main arteries in the low speed network, not the junctions that exist for some control modules. If an open-circuit is suspected in a cable or a short-circuit is suspected in one of its junctions, the connector at this unit must be disconnected and the reading taken from this unit.
Take the following readings
- Resistance between C1:49and C1:50. Resistance should be 120 ohms.
Note! Measuring will only give value 120 ohms if the main circuit in the CAN-net is intact. If there is a short-circuit somewhere in the CAN-net (either main circuit or other branching) the resistance will be 0 ohms.
- The resistance between C1:49 and a connection to voltage as well as between C1:49 and a short-circuit to ground. The resistance shall be very high (more than 1 Mohms).
- The resistance between C1:50 and a connection to voltage as well as between C1:50 and a short-circuit to ground. The resistance shall be very high (more than 1 Mohms).
Hint: If a fault is found, try to disconnect the junction with the fault at a point further forward. Disconnect any connector/control module immediately before the measurement point and take the reading again. Try to locate the fault in this way.
Remedy as necessary.
Other information
- Battery, disconnecting Battery Disconnecting
- Connecting the breakout box For Connection Of Breakout Box To Central Electronic Module (CEM)
- Signal specification Signal Description Central Electronic Module (CEM)
- Checking wiring and terminals Checking Wiring And Terminals
- See also Design and Function, CAN-network.
Was a fault detected?
Yes - Verification
No - Checking the traffic load on the CAN cables
-------------------------------------------------
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 the CAN network (both 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 the CAN network may be due to a control module sending faulty messages that disrupt "normal" communication. When messages are sent incorrectly, this results in a considerable increase in the amount of traffic on the CAN network. Check the load by measuring the average voltage value on the CAN cables in relation to ground.
Check as follows:
- Measure the voltage between C1:49 and ground. The voltage shall be approx. 2.3 V.
- Measure the voltage between C1:50 and ground. The voltage shall be approx. 2.8 V.
Other information
- Battery, disconnecting Battery Disconnecting
- See also Design and Function, CAN-network.
Is the value OK?
Yes - Fault-tracing without result
No - Identifying a control module in the CAN network
-------------------------------------------------
Identifying a control module in the CAN network
If the load on the CAN network is too high, this may be due to a control module transmitting faulty messages on the CAN network. This is called a disruptive control module. 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 the CAN network starting to send faulty messages. An intermittent short-circuit may occur without a diagnostic trouble code (DTC) being stored by any of the control modules.
Note! It is not necessarily the control module that has set the diagnostic trouble code that communicates incorrectly. Faulty messages can come from any control module in the same section of the CAN network. 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.
Check communication/load on CAN-net by measuring voltage between C1:49 and C1:50. 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. Switch off the ignition 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. See Repairing and installing/Removing, replacing and installing.
Note! Following a fault involving control modules that disrupt communication, other control modules may operate 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
-------------------------------------------------
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 car. Allow the car 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
-------------------------------------------------
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
------------------------
Attempt New Test - General information
-------------------------------------------------
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
------------------------
No Fault Found - DONE
Attempt New Test - General information
-------------------------------------------------
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
-------------------------------------------------