AUTO A/C DIAGNOSIS
TSB Revision
HEATER, AIR CONDITIONING AND VENTILATION
55-47
STEP 2. Recheck for diagnostic trouble code.
Check again if the DTC is set.
(1) Connect scan tool MB991958 to the data link connector
(2) Turn the ignition switch to the "ON" position.
(3) Check if the DTC is set.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the DTC set?
YES : Replace the A/C-ECU. On completion, check that the
DTC is not reset.
NO : There is an intermittent malfunction such as poor
engaged connector(s) or open circuit (Refer to
GROUP 00, How to Use Troubleshooting/Inspection
Service Points
− How to Cope with Intermittent
Malfunctions
P.00-15
.)
DTC U0141: ETACS-ECU Time-out
CAUTION
If DTC U0141 is set in the A/C-ECU, diagnose the
CAN main bus line.
CAUTION
Whenever the ECU is replaced, ensure that the
communication circuit is normal.
.
TROUBLE JUDGMENT
The A/C-ECU receives air conditioning opera-
tion-related signals from the ETACS-ECU via the
CAN bus lines. If the ECU cannot receive any of the
air conditioning control-related signals from the
ETACS-ECU, the diagnostic trouble code U0141 is
stored.
.
TECHNICAL DESCRIPTION (COMMENT)
Current trouble
• Connector(s) or wiring harness in the CAN bus
lines between the ETACS-ECU and the
A/C-ECU, the power supply system to the
ETACS-ECU, the ETACS-ECU itself, or the
A/C-ECU may be defective.
Past trouble
• If DTC U0141 is stored as a past trouble, carry
out diagnosis with particular emphasis on wiring
and connector(s) in the CAN bus line between
the A/C-ECU and the ETACS-ECU, and the
power supply system to the ETACS-ECU. If the
connectors and wiring are normal, and obviously
the ECU is the cause of the trouble, replace the
ECU. If in doubt, do not replace the ECU.
NOTE: For a past trouble, you cannot find it by
the scan tool CAN bus diagnostics even if there is
a failure in CAN bus lines. In this case, refer to
GROUP 00, How to Use Troubleshooting/Inspec-
tion Service Points
−
How to Cope with Intermit-
tent Malfunctions
P.00-15
) and check the CAN
bus lines. You can narrow down the possible
cause of the trouble by referring to the DTC,
which is set regarding the CAN communica-
tion-linked ECUs (Refer to GROUP 54C, Expla-
nation about the scan too CAN bus diagnostics
P.54C-14
).
.
TROUBLESHOOTING HINTS
• Malfunction of the A/C-ECU
• Malfunction of the ETACS-ECU
• Damaged harness wires and connectors