Diagnostics Item 4

DIAGNOSTIC ITEM 4: Diagnose the terminator resistors

CAUTION:
When servicing a CAN bus line, ground yourself by touching a metal object such as an unpainted water pipe. If you fail to do so, a component connected to the CAN bus line may be damaged.






















FUNCTION

The resistance in the communication errors condition cannot be measured by the CAN bus diagnostics, therefore, judge the terminator resistor only when receiving the each ECU periodically sent data normally.

TROUBLE JUDGMENT CONDITIONS

The scan tool MB991958 judges the trouble when the periodically sent data from each ECU can be received normally but the resistance value between CAN_H and CAN_L line is other than from 50 ohms to 70 ohms.

TROUBLESHOOTING HINTS

- The combination meter may be defective (malfunction of the terminator resistor)
- The ECM[ M/T] or PCM[ A/T] may be defective (malfunction of the terminator resistor)
- The wiring harness may be defective (larger resistance of harness between the combination meter and the ECM[ M/T] or PCM[ A/T])

DIAGNOSIS

Required Special Tools:

- MB991223: Harness Set
- MB992006: Extra fine probe
- MB991923: Power plant ECU Check Harness

STEP 1. Check the terminator resistor inside the combination meter. Measure the resistance at combination meter connector C-04.

CAUTION:
A digital multimeter should be used. For details refer to Precautions When CAN Bus Line(s) are Repaired.





(1)Disconnect combination meter C-04, and measure the resistance at the component side of combination meter connector C-04.





(2)Measure the resistance between combination meter connector terminals 3 and 4.
OK: 120± 20 ohms

Q. Does the resistance measure 120± 20 ohms?

YES Go to Step 2.

NO Replace the combination meter.

STEP 2. Check the terminator resistor inside the ECM [M/T] or PCM [A/T]. Measure the resistance at ECM [M/T] or PCM [A/T] connector B-18.









(1)Disconnect ECM [M/T] or PCM [A/T] connector B-18, and measure the resistance at the component side of ECM [M/T] or PCM [A/T] connector B-18.





(2)Measure the resistance between ECM [M/T] or PCM [A/T] connector terminals 17 and 18.
OK: 120± 20 ohms

Q. Does the resistance measure 120± 20 ohms?

YES Repair the wiring harness between combination meter connector and the ECM [M/T] or PCM [A/T] connector.

NO Replace the ECM [M/T] or PCM [A/T]. When the ECM [M/T] or PCM [A/T] is replaced, register the encrypted code. Encrypted Code Registration Criteria Table.