If DTC U0197 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 the air conditioning control-related signals from the hands-free
module via the CAN bus lines. If any of the air conditioning control-related signals from the
SRS-ECU cannot be received, the diagnostic trouble code U0197 is stored.
TECHNICAL DESCRIPTION (COMMENT)
Current trouble
Connector(s) or wiring harness in the CAN bus lines between the hands free module
and the A/C-ECU, the power supply system to the hands free module, the hands free module
itself, or the A/C-ECU may be defective.
Past trouble
Carry out diagnosis with particular emphasis on connector(s) or wiring harness in
the CAN bus lines between the A/C-ECU and the audio system, and the power supply system
to the audio system. For diagnosis procedures, refer to "How to treat past trouble" (Refer to
GROUP 00 -
How to Treat Past Trouble ).
note
For a past trouble, you can not find it by the M.U.T.-III CAN bus diagnostics even if
there is any failure in CAN bus lines. In this case, refer to GROUP 00, How to Cope with Intermittent Malfunction and
check the CAN bus lines. You can narrow down the possible cause of the trouble by referring
to the diagnosis code, which is set regarding the CAN communication-linked ECUs (Refer to GROUP
54C -
CAN Bus Line Diagnostic Flow ).
caution
If the ignition switch is turned to the ON position without
starting the engine, the diagnosis code U0184 (past trouble) may be set to the A/C-ECU after
three minutes.
PROBABLE CAUSES
Damaged harness wires and connectors
Malfunction of audio
Malfunction of the A/C-ECU
DIAGNOSIS PROCEDURE
Required Special Tools:
MB991223: Harness Set
MB992006: Extra Fine Probe
MB991958: Scan Tool (M.U.T.-III Sub Assembly)
MB991824: V.C.I.
MB991827: M.U.T.-III USB Cable
MB991910: M.U.T.-III Main Harness A
STEP 1. M.U.T.-III CAN bus diagnostics
Use the M.U.T.-III to diagnose the CAN bus lines.
Q.
Is the check result normal?
Go to Step 2
Repair the CAN bus lines. (Refer to GROUP 54C, Troubleshooting ).
On completion, go to Step 6.
STEP 2. M.U.T.-III other system diagnosis code
Check whether the audio-related diagnosis code is set.
Q.
Is the diagnosis code set?
Diagnose the audio. Refer to .
Go to Step 3
STEP 3. M.U.T.-III other system diagnosis code
Check if a diagnosis code, which relates to CAN communication-linked systems below, is
set.
combination meter U0184: audio-related time-out diagnosis code
Q.
Is the diagnosis code set?
Go to Step 4
Go to Step 5
STEP 4. Check whether the diagnosis code is reset.
Recheck if the diagnosis code is set.
(1)Erase the diagnosis code.
(2)Ignition switch: LOCK (OFF) to ON
(3)Check if the diagnosis code is set.
Q.
Is the diagnosis code set?
Replace the audio, and then go to Step 6.
A poor connection, open circuit or other intermittent malfunction in the CAN bus
line between the audio and the A/C-ECU. (Refer to GROUP 00 -
How to Cope with
Intermittent Malfunction ).
STEP 5. Check whether the diagnosis code is reset.
Recheck if the diagnosis code is set.
(1)Erase the diagnosis code.
(2)Ignition switch: LOCK (OFF) to ON
(3)Check if the diagnosis code is set.
Q.
Is the diagnosis code set?
Replace the A/C-ECU, and then go to Step 6.
A poor connection, open circuit or other intermittent malfunction in the CAN bus
line between the audio and the A/C-ECU. (Refer to GROUP 00 -
How to Cope with
Intermittent Malfunction ).
STEP 6. Check whether the diagnosis code is reset.
). 
