Diagnostic Item 4

DIAGNOSTIC ITEM 4: Diagnose the terminator resistors

Part 1:

Part 1:

Part 2:

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 JUDGEMENT 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 or PCM 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 or PCM )

DIAGNOSIS

Required Special Tools:
- MB991223: Harness Set
- MB992006: Extra fine probe

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.

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 or PCM . Measure the resistance at ECM or PCM connector B-18.

1. Disconnect ECM or PCM connector B-18, and measure the resistance at the component side of ECM or PCM connector B-18.

2. Measure the resistance between ECM or PCM 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 or PCM connector.

NO: Replace the ECM or PCM . When the ECM or PCM is replaced, register the encrypted code. Refer to Chassis Electrical - Encrypted Code Registration Criteria Table.