Automatic Air Conditioning

DTC U1073: Bus Off

CAUTION:
If DTC U1073 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

If the A/C-ECU ceases communicating once (i.e. bus off) and then returns to it, the A/C-ECU will not communicate for three minutes immediately after that point. This three-minute period is called "Penalty mode." Immediately after the A/C-ECU returns to communication, the DTC is set.

PROBABLE CAUSES

- Malfunction of connector.
- Malfunction of the harness (CAN line is open/shorted to ground)
- Malfunction of the A/C-ECU

DIAGNOSIS

Required Special Tools:

- MB991223: Harness Set
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991910: Main Harness A

STEP 1. Using scan tool MB991958, diagnose the CAN bus line.





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)Turn the ignition switch to the "ON" position.
(3)Diagnose the CAN bus line.
(4)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is the CAN bus line found to be normal?

YES Go to Step 2.

NO Repair the CAN bus lines Precautions on How to Repair the CAN Bus Line(s)).

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 check result satisfactory?

YES There is an intermittent malfunction such as poor engaged connector(s) or open circuit How to Cope With Intermittent Malfunctions).
NO Go to Step 3.
STEP 3. Replace the A/C-ECU and then recheck the DTC.

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 check result satisfactory?

YES The procedure is complete.
NO Go to Step 1.