Fault-Tracing Information
Fault-tracing
General information
Note! During this fault-tracing use the wiring diagram to provide support when taking readings.
The diagnostic trouble code (DTC) is stored in the event of communication faults on the high speed side of the control area network (CAN). There can be a number of causes for faults in the communication:
- 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
- Fault in the communication circuit in one or more control modules
- Internal fault in a control module on the CAN network that results in the control module transmitting faulty messages on the CAN network.
In the event of a diagnostic trouble code (DTC) for a communication fault in the relevant control module, any diagnostic trouble codes (DTCs) in the central electronic module (CEM) must also be checked. The central electronic module (CEM) monitors the voltage level in the CAN cables. The central electronic module (CEM) is the only control module that can directly store a diagnostic trouble code (DTC) for a short-circuit in one of the cables for ground or supply voltage. Do not replace the central electronic module (CEM) in the event of a CAN fault unless fault-tracing has indicated that the central electronic module (CEM) has an internal fault.
In order to check the control area network (CAN) cables, the resistance in the network must be measured.
Other information
- General information about fault-tracing in the CAN network General Information About Fault-Tracing In The CAN Network
Continue - Taking reading on cable in the CAN network (HS-CAN)
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Taking reading on cable in the CAN network (HS-CAN)
- Disconnect the battery negative lead.
- Connect the breakout box with the engine control module (ECM) connected.
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.
Hint: Use the wiring diagram to provide support when taking readings.
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 measure the main arteries in the high speed network, not the junctions that exist for some control modules. See the wiring diagram for the relevant car model. If an open-circuit is suspected in a cable, or a short-circuit is suspected in one of its junctions, the connector at the control module for this junction must be disconnected and the reading taken from there.
Take the following readings
- Measure the resistance between the terminals for HS CAN on the Engine control module (ECM). Resistance must be approximately 60 ohms. Permitted values are approximately 55 - 65 ohms.
Note! If there is a short-circuit somewhere in the CAN-net (either main circuit or other branching) the resistance will be 0 ohms.
- Also measure the resistance between each terminal and supply voltage and ground. The resistance shall be very high (more than 1 Mohms).
Hint: Any short-circuit detected on the CAN-net may be on the main circuit or on any branching running out to some control modules. 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.
Remedy as necessary.
Other information
- Battery, disconnecting Battery, Disconnecting
- Connecting the breakout box, B6324S5 Connecting The Breakout Box, Engine Control Module (ECM)
- Signal specification, engine control module (ECM), B6324S5 Signal Specification, Engine Control Module (ECM)
- Checking wiring and terminals Checking Wiring And Terminals
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 battery.
- Ignition on.
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:
- Connect a voltmeter between CAN-L and ground. The voltage should be approx:1,8-2,2V
- Connect a voltmeter between CAN-H and ground. The voltage should be approx:2,8-3,2V
Other information
- Battery, disconnecting Battery, Disconnecting
Is the value OK?
Yes - Fault-tracing without result
No - Identifying a control module in the CAN network
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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 sending faulty messages on the CAN network (known as 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. The faults can occur without a diagnostic trouble code (DTC) being stored by the control modules. The voltage can be measured between the CAN cables in order to check the load on the CAN network.
Take the following readings
- Connect a voltmeter between the CAN cables. The average value of the voltage must be approximately 0.6-1.4 V. In case of a problem with communication the voltage is considerably higher.
- In order to identify which control module has faulty communication, 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. Repeat until the voltage between the CAN wiring drops to the normal level.
Note! When connecting and disconnecting certain control modules, diagnostic trouble codes (DTCs) may be stored in other control modules.
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.
A control module that is communicating incorrectly must be replaced. Remedy as necessary.
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.
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.
Does the diagnostic trouble code (DTC) for faulty communication return?
Yes - Fault-tracing information
No - FAULT FOUND
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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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