Can Bus Waveforms
HINT:
- This waveform is measured between terminals CANH and GND, and terminals CANL and GND of the DLC3. (Use this as a reference for diagnosis of CAN communication lines.)
- When malfunctions in multiple ECUs are suspected based on the CAN bus check and DTCs checked using the Techstream, check the resistance of the CAN bus using an ohmmeter first. If no problems are found, check the following waveforms.
Refer to HOW TO PROCEED WITH TROUBLESHOOTING [09/2014 - 11/2017]
- If a waveform is not similar to one of the following 3 patterns (Group 1), then an open in a CAN main bus line, an open in a CAN branch line, or a short between a CAN line (CANH or CANL) and ground is suspected (Group 2).
- Wiggle the connector and wire harness to check if the waveform changes.
- CAN bus waveforms (Group 1)
- Normal waveform
- Open in both of the lines (CANH and CANL) of a CAN branch
HINT:
- Waveforms (waveforms shown using dotted lines) are not present from an ECU or sensor connected to a CAN branch with an open circuit in both lines. (Waveforms from other ECUs or sensors are normal.)
- Because this waveform is similar to a normal waveform, instead of using the waveform, the malfunctioning part can be narrowed down by performing a CAN bus check.
- Short between the CAN bus lines (CANH and CANL)
HINT:
- Waveforms disappear.
- If the malfunction is in an ECU, disconnecting the ECU will change the waveform. If the waveform does not change, a malfunction in the wire harness is suspected.
- Normal waveform
- CAN bus waveforms (reference) (Group 2)NOTE:
The following CAN bus waveforms can be used only as reference. The actual measured waveform may differ significantly depending on the location of the open or short circuit.
- Open in a CAN branch line (CANH)
HINT:
- An abnormal waveform is output from an ECU with an open in one of its CAN branch lines. Because this abnormal output interferes with the signals from other ECUs, the output of other ECUs will also appear abnormal.
- Narrow down the malfunctioning part by checking DTCs or performing a CAN bus check, or by checking waveform changes when ECUs or sensors are disconnected. The waveform will change to one for an open in both sides of a CAN branch when the ECU or sensor with an open CAN branch line is disconnected.
- Open in a CAN branch line (CANL)
HINT:
- An abnormal waveform is output from an ECU with an open in one of its CAN branch lines. Because this abnormal output interferes with the signals from other ECUs, the output of other ECUs will also appear abnormal.
- Narrow down the malfunctioning part by checking DTCs or performing a CAN bus check, or by checking waveform changes when ECUs or sensors are disconnected. The waveform will change to one for an open in both sides of a CAN branch when the ECU or sensor with an open CAN branch line is disconnected.
- Open in a CAN main bus line (CANH)
HINT:
- Waveforms of ECUs or sensors that are closer to the DLC3 than the open part are almost normal.
- Waveforms of ECUs or sensors that are on the opposite side of the DLC3 from the open part are abnormal.
- An open in a CAN main bus line can be confirmed by measuring the resistance between the CANH and CANL terminals of any CAN branch.
- Short between a CAN bus line (CANH) and ground
HINT:
- Narrow down the shorted part by checking for waveform changes when disconnecting connectors from the CAN junction connectors or when disconnecting ECUs or sensors.
- A short to ground in the CANH line can be confirmed by measuring the resistance between CANH and ground using an ohmmeter.
- Short between a CAN bus line (CANL) and ground
HINT:
- Narrow down the shorted part by checking for waveform changes when disconnecting connectors from the CAN junction connectors or when disconnecting ECUs or sensors.
- A short to ground in the CANL line can be confirmed by measuring the resistance between CANL and ground using an ohmmeter.
- Open in a CAN branch line (CANH)