Diagnostic Item 7

DIAGNOSTIC ITEM 7: Diagnose when the scan tool cannot receive the data sent by A/C-ECU.









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 diagnostic result demonstrates that "the scan tool cannot receive the sent data from the A/C-ECU" when the scan tool MB991958 checks the periodically sent data from each ECU and cannot receive the A/C-ECU data only.

TROUBLE JUDGEMENT CONDITIONS
Scan tool MB991958 judges the trouble when the periodically sent data from A/C-ECU cannot be received and sent.

TROUBLESHOOTING HINTS
- The wiring harness may be defective [open circuit between A/C-ECU and joint connector (3) ]
- The connector may be defective [poor connection of joint connector (3) or A/C-ECU connector]
- Power supply circuit malfunction of the A/C-ECU
- The A/C-ECU may be defective

DIAGNOSIS

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







STEP 1. Check joint connector (3) C-03 and A/C-ECU connector C-14 or C-15 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

CAUTION: The strand end of the twisted wire should be within 10 cm (4.0 inches) from the connector.




Check the joint connector at the wiring harness side for loose, corroded or damaged terminals, or terminals pushed back in the connector, and also check the short pin behind the connector for corrosion, deformation and delamination.

Q: Are joint connector (3) C-03 and A/C-ECU connector C-14 or C-15 in good condition?

YES: Go to Step 2.

NO: Repair the damaged parts. Replace the joint connector as necessary.

STEP 2. Check the CAN bus lines between joint connector (3) C-03 and the A/C-ECU. Measure the resistance between joint connector (3) C-03 and A/C-ECU connector C-14 or C-15 .

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

1. Disconnect joint connector (3) C-03 and A/C-ECU connector C-14 or C-15 , and measure the resistances at the wiring harness sides of joint connector (3) C-03 and A/C-ECU connector C-14 or C-15 .

2. Measure the resistance between joint connector (3) C-03 (terminal 6) and A/C-ECU connector C-14 (terminal 5) or A/C-ECU connector C-15 (terminal15) .

OK: 2 ohms or less

CAUTION: Strictly observe the specified wiring harness repair procedure.

3. Measure the resistance between joint connector (3) C-03 (terminal 17) and A/C-ECU connector C-14 (terminal 6) or A/C-ECU connector C-15 (terminal 14) .

OK: 2 ohms or less

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

YES: Diagnose the air conditioning system. Refer to Manual A/C diagnosis or Auto A/C diagnosis .

NO: Repair the wiring harness between joint connector (3) C-03 and the A/C-ECU connector C-14 or C-15.