CAN L short-circuited to ground bus waveform-EEWORLD

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When a CAN L short-circuit to ground fault occurs, depending on the fault-tolerance characteristics of the CAN bus, the entire CAN network may be unable to communicate or a related fault code may be generated.

However, for some car series, such as the Haima series, the fault tolerance characteristics of the CAN L short circuit to ground are better, and the vehicle can basically be used normally, that is, there is no obvious abnormality at the customer experience level, but from a diagnostic point of view, it will affect the network transmission speed.

At this time, the CAN L voltage is about 0 V. The recessive voltage of the CAN H line is reduced to 0 V, but the dominant voltage remains basically unchanged, so the waveform is elongated and data can still be transmitted, which explains why the fault tolerance of CAN L to ground short circuit is good.

The bus waveform when CAN L is short-circuited to ground is shown in the figure below.

When measuring the CAN line voltage, if the CAN L voltage is 0V and the CAN H voltage is about 1V, this indicates that this type of fault has occurred. The CAN L
voltage when CAN L is short-circuited to ground is shown in the figure below.

The CAN H voltage when CAN L is short-circuited to ground is shown in the figure below.

Cause of the fault: If the fault is not caused by the short circuit of the CAN-L wire to the external ground wire, then this fault is caused by the damage of the CAN transceiver inside the control module. The fault finding method is the same as above.

Keywords：CAN Reference address：CAN L short-circuited to ground bus waveform

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