Diagnostic Item 2

DIAGNOSTIC ITEM 2: Diagnose shorts in the ground to CAN bus line

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
when diagnosing the CAN bus lines, the scan tool MB991958 measures the voltage of CAN_H and CAN_L line and detects the short to power supply or ground.

TROUBLE JUDGEMENT CONDITIONS
The scan tool MB991958 judges the trouble when it is impossible to receive the periodically sent data and the voltage of CAN_H or CAN_L line is less than 1.0 volt.

TROUBLESHOOTING HINTS
- The wiring harness may be defective (CAN bus lines or the wiring harness between the data link connector and joint connector (3) for short to ground)
- The connectors may be defective (short to ground in the connector)
- Each ECU may be defective (short to ground in the ECU)

DIAGNOSIS

Required Special Tools:
- MB991223: Harness Set
- MB992006: Extra Fine Probe
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A

- MB991970: ABS Check Harness

STEP 1. Check the CAN bus lines for short to ground. Measure the resistance at data link connector C-125.

CAUTION:
- A digital multimeter should be used.
- The test wiring harness should be used.

NOTE: This inspection allows you to check that there is a short to ground in either CAN_H line or CAN_L line.

CAUTION: Disconnect the negative battery terminal.

1. Disconnect the negative battery terminal.

2. Disconnect ECM or PCM connector B-18 and combination meter connector C-04, and measure the resistance at the harness side of data link connector C-125.

3. Measure the resistance between data link connector terminal 6 (CAN_H) and body ground.

OK: 1 k Ohm or more

4. Measure the resistance between data link connector terminal 14 (CAN_L) and body ground.

OK: 1 k ohm or more

Q: Is the check result normal?

YES: Go to Step 17.

NO: Go to Step 2.

STEP 2. Check the CAN bus line of the front wiring harness for short to ground. Measure the resistance at intermediate connector C-24 or C-23 .

CAUTION: Disconnect the negative battery terminal.

1. Disconnect the negative battery terminal.

2. Disconnect intermediate connector C-24, and measure the resistance at the male side (at front wiring harness side).

3. Measure the resistance between intermediate connector (C-24) terminal 11 (CAN_H) and body ground.

OK: 1 k ohm or more

4. Measure the resistance between intermediate connector (C-24) terminal 12 (CAN_L) and body ground.

OK: 1 k ohm or more

5. Measure the resistance between intermediate connector (C-23) terminal 22 (CAN_H) and body ground.

OK: 1 k ohm or more

6. Measure the resistance between intermediate connector (C-23) terminal 23 (CAN_L) and body ground.

OK: 1 k ohm or more

Q: Is the check result normal?

YES: Go to Step 3.

NO : Go to Step 11.
NO : Go to Step 12.

STEP 3. Check the CAN line between joint connector (3) and the combination meter for short to ground. Measure the resistance at joint connector (3) C-03.

CAUTION: Disconnect the negative battery terminal.

1. Disconnect the negative battery terminal.

2. Disconnect joint connector (3) C-03, and measure the resistance at the wiring harness side of joint connector (3) C-03.

3. Measure the resistance between joint connector (3) terminal 4 (CAN_H) and body ground.

OK: 1 k ohm or more

4. Measure the resistance between joint connector (3) terminal 15 (CAN_L) and body ground.

OK: 1 k ohm or more

CAUTION: Strictly observe the specified wiring harness repair procedure.

Q: Is the check result normal?

YES: Go to Step 4.

NO: Repair the wiring harness between joint connector (3) and the combination meter connector.

STEP 4. Check the CAN line between joint connector (3) and the ETACS-ECU connector for short to ground. Measure the resistance at joint connector (3) C-03.

CAUTION: Disconnect the negative battery terminal.

1. Disconnect the negative battery terminal.

2. Disconnect joint connector (3) C-03, and measure the resistance at the wiring harness side of joint connector (3) C-03.

3. Measure the resistance between joint connector (3) terminal 5 (CAN_H) and body ground.

OK: 1 k ohm or more

4. Measure the resistance between joint connector (3) terminal 16 (CAN_L) and body ground.

OK: 1 k ohm or more

Q: Is the check result normal?

YES: Go to Step 5.

NO: Go to Step 8.

STEP 5. Check the CAN line between joint connector (3) and the A/C-ECU connector for short to ground. Measure the resistance at joint connector (3) C-03.

CAUTION: Disconnect the negative battery terminal.

1. Disconnect the negative battery terminal.

2. Disconnect joint connector (3) C-03, and measure the resistance at the wiring harness side of joint connector (3) C-03.

3. Measure the resistance between joint connector (3) terminal 6 (CAN_H) and body ground.

OK: 1 k ohm or more

4. Measure the resistance between joint connector (3) terminal 17 (CAN_L) and body ground.

OK: 1 k ohm or more

Q: Is the check result normal?

YES: Go to Step 6.

NO: Go to Step 9.

STEP 6. Check the CAN line between joint connector (3) and the SRS-ECU connector for short to ground. Measure the resistance at joint connector (3) C-03.

CAUTION: Disconnect the negative battery terminal.

1. Disconnect the negative battery terminal.

2. Disconnect joint connector (3) C-03, and measure the resistance at the wiring harness side of joint connector (3) C-03.

3. Measure the resistance between joint connector (3) terminal 3 and body ground.

OK: 1 k ohm or more

4. Measure the resistance between joint connector (3) terminal 14 and body ground.

OK: 1 k ohm or more

Q: Does the resistance measure 1 k ohm or more?

YES: Go to Step 7.

NO: Go to Step 10.

STEP 7. Check the CAN line between joint connector (3) and the data link connector for short to ground. Measure the resistance at joint connector (3) C-03.

CAUTION: Disconnect the negative battery terminal.

1. Disconnect the negative battery terminal.

2. Disconnect joint connector (3) C-03, and measure the resistance at the wiring harness side of joint connector (3) C-03.

3. Measure the resistance between joint connector (3) terminal 7 (CAN_H) and body ground.

OK: 1 k ohm or more

4. Measure the resistance between joint connector (3) terminal 18 (CAN_L) and body ground.

OK: 1 k ohm or more

CAUTION: Strictly observe the specified wiring harness repair procedure.

Q: Does the resistance measure 1 k ohm or more?

YES: Repair the wiring harness between joint connector (3) and the intermediate connector.

NO: Repair the wiring harness between joint connector (3) and the data link connector.

STEP 8. Check the ETACS-ECU for a short to ground.

1. Disconnect ETACS-ECU connector C-218.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

2. Connect scan tool MB991958 to the data link connector.

3. Diagnose CAN bus lines, and check if scan tool MB991958 screen is as shown in the illustration.

Q: Does scan tool MB991958 screen correspond to the illustration?

YES: Repair the wiring harness between joint connector (3) and the ETACS-ECU connector.

NO: Check the ETACS-ECU connector, and repair if necessary. If the ETACS-ECU connector is in good condition, replace the ETACS-ECU. When the ETACS-ECU is replaced, register the encrypted code. Refer to Chassis Electrical - Encrypted Code Registration Criteria Table.

STEP 9. Check the A/C-ECU for a short to ground.

1. Disconnect A/C-ECU connector C-14 or C-15 .

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

2. Connect scan tool MB991958 to the data link connector.

1. Disconnect SRS-ECU connector C-123.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

2. Connect scan tool MB991958 to the data link connector.

3. Diagnose CAN bus lines, and check if scan tool MB991958 screen is as shown in the illustration.

Q: Does scan tool MB991958 screen correspond to the illustration?

YES: Repair the wiring harness between joint connector (3) and the SRS-ECU connector.

NO: Check the SRS-ECU connector, and repair if necessary. If the SRS-ECU connector is in good condition, replace the SRS-ECU.

STEP 11. Check the CAN line between intermediate connector C-24 and ABS-ECU or ABS/TCL-ECU connector for a short to ground. Measure the resistance at intermediate connector C-24.

CAUTION: Disconnect the negative battery terminal.

1. Disconnect the negative battery terminal.

2. Disconnect intermediate connector C-24 and ABS-ECU connector A-02 or ABS/TCL-ECU connector A-03 , and measure the resistance at the male side of intermediate connector C-24 (at front wiring harness side).

3. Measure the resistance between intermediate connector terminal 11 (CAN_H) and body ground.

OK: 1 k ohm or more

4. Measure the resistance between intermediate connector terminal 12 (CAN_L) and body ground.

OK: 1 k ohm or more

CAUTION: Strictly observe the specified wiring harness repair procedure.

Q: Is the check result normal?

YES: Go to Step 15.

NO: Repair the wiring harness.

STEP 12. Check the CAN line of the front wiring harness for a short to the power supply. Measure the resistance at intermediate connector C-26.

1. Disconnect intermediate connector C-26, and measure the resistance at the male side (at front wiring harness side).
2. Turn the ignition switch to the "ON" position.

3. Measure the resistance between intermediate connector terminal 15 (CAN_H) and body ground.

OK: 1 k ohm or more

4. Measure the resistance between intermediate connector terminal 16 (CAN_L) and body ground.

OK: 1 k ohm or more

Q:: Is the check result normal?

YES: Go to Step 15.

NO: Go to Step 13.

STEP 13. Check the CAN bus lines between intermediate connector C-26 and convertible top control module connector D-45. Measure the resistance between intermediate connector C-26 and convertible top control module connector D-45.

CAUTION:
- A digital multimeter should be used.
- The test wiring harness should be used.

1. Disconnect intermediate connector C-26 and convertible top control module connector D-45, and measure the resistance between the wiring harness side connector of convertible top control module connector D-45 and the male side connector of intermediate connector C-26 (at front wiring harness side).
2. Turn the ignition switch to the "LOCK" (OFF) position.

CAUTION: Disconnect the negative battery terminal.

3. Disconnect the negative battery terminal.

4. Measure the resistance between intermediate connector C-26 (terminal 15) and convertible top control module connector D-45 (terminal 37).

OK: 2 ohms or less

5. Measure the resistance between intermediate connector C-26 (terminal 16) and convertible top control module connector D-45 (terminal 38).

OK: 2 ohms or less

CAUTION: Strictly observe the specified wiring harness repair procedure.

Q: Do all the resistances measure 2 ohms or less?

YES: If all the resistances measure 2 ohms or less, go to Step 14.

NO: If either of the resistances measures more than 2 ohms or all the resistances measure more than 2 ohms, repair the wiring harness between intermediate connector C-26 and the convertible top control module connector D-45.

STEP 14. Check the CAN bus lines between intermediate connector C-23 and the convertible top control module connector D-45. Measure the resistance between intermediate connector C-23 and convertible top control module connector D-45.

CAUTION:
- A digital multimeter should be used.
- The test wiring harness should be used.

1. Disconnect intermediate connector C-23 and convertible top control module connector D-45, and measure the resistance between the wiring harness side connector of convertible top control module connector D-45 and the male side connector of intermediate connector C-23 (at front wiring harness side).
2. Turn the ignition switch to the "LOCK" (OFF) position.

CAUTION: Disconnect the negative battery terminal.

3. Disconnect the negative battery terminal.

4. Measure the resistance between intermediate connector C-23 (terminal 22) and convertible top control module connector D-45 (terminal 48).

OK: 2 ohms or less

5. Measure the resistance between intermediate connector C-23 (terminal 23) and convertible top control module connector D-45 (terminal 49).

OK: 2 ohms or less

Q: Do all the resistances measure 2 ohms or less?

YES: Check the convertible top control module connector D-45, and repair if necessary. If the convertible top control module connector D-45 is in good condition, replace the convertible top control module.

NO: If either of the resistances measures more than 2 ohms or all the resistances measure more than 2 ohms, repair the wiring harness between intermediate connector C-23 and the convertible top control module connector D-45.

STEP 15. Check the CAN line between the ECM or PCM connector and ABS-ECU or ABS/TCL-ECU connector for a short to ground. Measure the resistance at ECM or PCM connector B-18.

CAUTION: Disconnect the negative battery terminal.

1. Disconnect the negative battery terminal.
2. Disconnect ECM or PCM connector B-18 and ABS-ECU connector A-02 or ABS/TCL-ECU connector A-03 , and measure the resistance at the harness side of ECM or PCM connector B-18.

3. Measure the resistance between ECM or PCM connector terminal 17 and body ground.

OK: 1 k ohm or more

4. Measure the resistance between ECM or PCM connector terminal 18 and body ground.

OK: 1 k ohm or more

CAUTION: Strictly observe the specified wiring harness repair procedure.

Q: Is the check result normal?

YES: Go to Step 16.

NO: Repair the wiring harness between ECM or PCM connector and ABS-ECU or ABS/TCL-ECU connector.

STEP 16. Retest the system.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

1. Connect scan tool MB991958 to the data link connector.
2. Diagnose CAN bus lines, and check if scan tool MB991958 screen shows normal state.

Q: Is the check result normal?

YES: Intermittent malfunction.

NO: Check the ABS-ECU or ABS/TCL-ECU connector, and repair if necessary. If the ABS-ECU or ABS/TCL-ECU connector is in good condition, replace the ABS-ECU or ABS/TCL-ECU .

STEP 17. Check the combination meter for a short to ground.

1. Disconnect combination meter connector C-04.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

2. Connect scan tool MB991958 to the data link connector.

3. Diagnose CAN bus lines, and check if scan tool MB991958 screen is as shown in the illustration.

Q: Does scan tool MB991958 screen correspond to the illustration?

YES: Go to Step 18.

NO: Go to Step 19.

STEP 18. Check the ECM or PCM for a short to ground.

1. Disconnect ECM or PCM connector B-18.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

2. Connect scan tool MB991958 to the data link connector.

3. Diagnose CAN bus lines, and check if scan tool MB991958 screen is as shown in the illustration.

Q: Does scan tool MB991958 screen correspond to the illustration?

YES: Intermittent malfunction.

NO: Go to Step 20.

STEP 19. Retest the system.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

1. Connect scan tool MB991958 to the data link connector.
2. Diagnose CAN bus lines, and check if scan tool MB991958 screen shows normal state.

Q: Is the check result normal?

YES: Intermittent malfunction.

NO: Check the combination meter connector, and repair if necessary. If the combination meter connector is in good condition, replace the combination meter.

STEP 20. Retest the system.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

1. Connect scan tool MB991958 to the data link connector.
2. Diagnose CAN bus lines, and check if scan tool MB991958 screen shows normal state.

Q: Is the check result normal?

YES: Intermittent malfunction.

NO: Check the ECM or PCM connector, and repair if necessary. If the ECM or PCM connector is in good condition, 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.