If diagnosis code P1901 is set in the A/T-ECU,
always diagnose the CAN main bus line. If there is any fault in the CAN bus lines, an incorrect diagnosis
code may be set.
Whenever the ECU is replaced, ensure that the communication circuit is normal.
DIAGNOSIS CODE SET CONDITIONS
Current trouble
Connector(s) or wiring harness in the CAN bus lines between the engine-ECU and the
A/T-ECU, the power supply system to the engine-ECU, the engine-ECU itself, or the A/T-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 engine-ECU and the A/T-ECU, and the power supply system to the engine-ECU.
For diagnosis procedures, refer to "How to cope with past trouble" (Refer to GROUP 00, How to
Use Troubleshooting/Inspection Service Points ).
note
For a past trouble, you may 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 Use Troubleshooting/Inspection
Service Points -
How to Cope with Intermittent Malfunctions ). 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, Explanation about the M.U.T.-III CAN Bus Diagnostics ).
PROBABLE CAUSES
Damaged wiring harness or connector
Malfunction of the engine-ECU
Malfunction of the A/T-ECU
DIAGNOSIS PROCEDURE
STEP 1. M.U.T.-III CAN bus diagnostics
Using M.U.T.-III, perform CAN busline diagnosis.
Q.
Is the check result normal?
Go to Step 2.
Repair the CAN busline (Refer to GROUP54C, Diagnosis -
Can Bus Diagnostic
Chart ), and then go to Step 4.
STEP 2. M.U.T.-III other system diagnosis codes
Check whether the diesel fuel system diagnosis codes are set or not.
Q.
Is the diagnosis code output?
YES : Diagnose the diesel fuel system (Refer to GROUP 13A, Troubleshooting ).
Go to Step 3.
STEP 3. M.U.T.-III diagnosis code
Reconfirm whether the diagnosis codes are output from A/T-ECU.
(1)Erase the diagnosis code.
(2)Turn the ignition switch to ON position.
(3)Check if the diagnosis code is set.
Q.
Is the diagnosis code output?
Go to Step 4.
Intermittent malfunction in CAN busline between engine-ECU and A/T-ECU (Refer
to GROUP 00 -
How to Use Troubleshooting/Inspection Service Points -
How to
Cope with Intermittent Malfunction ).
STEP 4. Replace the engine-ECU
After replacing the engine-ECU, re-check the A/T diagnosis code output.
).
