Diagnostics Item 19

DIAGNOSTIC ITEM 19: Diagnose when the scan tool cannot receive the data sent by A/C-ECU [vehicles with A/C] or heater control unit [vehicles without A/C].

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

If the scan tool MB991958 cannot communicate with the A/C-ECU [vehicles with A/C] or heater control unit [vehicles without A/C], this diagnosis result will be set.

TROUBLE JUDGMENT CONDITIONS

If a communication flag is not set for the A/C-ECU [vehicles with A/C] or heater control unit [vehicles without A/C], the ETACS-ECU determines that there is a failure.

TROUBLESHOOTING HINTS

- Malfunction of the connector [joint connector (CAN1), A/C-ECU[ vehicles with A/C] or heater control unit[ vehicles without A/C] connector improperly connected]
- Malfunction of the wiring harness [open circuit between the A/C-ECU[ vehicles with A/C] or heater control unit[ vehicles without A/C] connector and the joint connector (CAN1), power supply circuit to the A/C-ECU[ vehicles with A/C] or heater control unit[ vehicles without A/C]]
- Malfunction of the A/C-ECU[ vehicles with A/C] or heater control unit[ vehicles without A/C]

DIAGNOSIS

Required Special Tools:

- MB991223: Harness Set
- MB992006: Extra Fine Probe

STEP 1. Check joint connector (CAN1) C-105 and A/C-ECU connector C-22 [vehicles with A/C] or heater control unit connector C-53 [vehicles without A/C] 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 inches) from the connector. For details refer to Precautions When CAN Bus Line(s) are Repaired.

Q. Are joint connector (CAN1) C-105 and A/C-ECU connector C-22[ vehicles with A/C] or heater control unit connector C-53[ vehicles without A/C] in good condition?

YES Go to Step 2.
NO Repair the damaged parts.
STEP 2. Check the wiring harness between joint connector (CAN1) C-105 and A/C-ECU connector C-22 [vehicles with A/C] or heater control unit connector C-53 [vehicles without A/C] for open circuit.

CAUTION:
Strictly observe the specified wiring harness repair procedure.
For details refer to Precautions When CAN Bus Line(s) are Repaired.

(1)Disconnect joint connector (CAN1) C-105 and A/C-ECU connector C-22 [vehicles with A/C] or heater control unit connector C-53 [vehicles without A/C], and check the wiring harness.





(2)Check the wiring harness between joint connector (CAN1) C-105 (terminal 1) and A/C-ECU connector C-22 [vehicles with A/C] or heater control unit connector C-53 [vehicles without A/C] (terminal 11)
OK: Continuity exists (2ohms or less)






(3)Check the wiring harness between joint connector (CAN1) C-105 (terminal 12) and A/C-ECU connector C-22 [vehicles with A/C] or heater control unit connector C-53 [vehicles without A/C] (terminal 12)
OK: Continuity exists (2ohms or less)

Q. Is the wiring harness between joint connector (CAN1) C-105 and A/C-ECU connector C-22[ vehicles with A/C] or heater control unit connector C-53[ vehicles without A/C] in good condition?

YES Check the power supply circuit of the A/C-ECU [vehicles with A/C]
or heater control unit [vehicles without A/C]. Symptom Chart Symptom Chart.

NO Repair the wiring harness between joint connector (CAN1) C-105 and A/C-ECU connector C-22 [vehicles with A/C] or heater control unit connector C-53 [vehicles without A/C].