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DTC B1731: Engine control module communication timeout
 
 
caution
  • When DTC B1731 is set, be sure to diagnose the CAN bus line.
  • When replacing the ECU, always check that the communication circuit is normal.
 
 
DTC SET CONDITION
WCM checks that the engine control module data has been received via the CAN bus lines, and if not, sets DTC No. B1731.
 
 
TECHNICAL DESCRIPTION (COMMENT)
If no data [ETACS transmits engine random number data to WCM via the CAN bus lines] is received from the engine control module via the CAN bus lines when the ignition switch is turned to ON position, it is judged as abnormal.
 
 
TROUBLESHOOTING HINTS
  • Malfunction of CAN bus line
  • Malfunction of WCM
  • Malfunction of ETACS-ECU
  • Damaged wiring harness and connectors
  • Malfunction of engine control module
 
 
DIAGNOSIS
STEP 1. Using scan tool MB991958, diagnose the CAN bus line.
(1)
cautionTo prevent damage to scan tool (MB991958), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (MB991958).
Connect scan tool MB991958. Refer to "How to connect the Scan Tool (M.U.T.-III) ."
(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.
Is the CAN bus line found to be normal?
Go to Step 2.
Repair the CAN bus line (Refer to GROUP 54C, Diagnosis ).
 
STEP 2. Using scan tool MB991958, read the engine control module diagnostic trouble code.
Check again if the DTC is set in the engine control module.
Is the DTC set?
Troubleshoot the MFI system (Refer to GROUP 13A, Diagnostic trouble code chart <2.0L ENGINE> or GROUP 13C, Diagnostic trouble code chart <2.4L ENGINE>).
Go to Step 3.
 
STEP 3. Using scan tool MB991958, read the other system diagnostic trouble code.
Check if DTC U0100 is set in the ETACS-ECU.
Is the DTC set?
Go to Step 5.
Go to Step 4.
 
STEP 4. Recheck for diagnostic trouble code.
Check again if the DTC is set in the WCM.
(1) Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
(2) Check if DTC is set.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is the DTC set?
Replace WCM and register the ID codes (Refer to ). After registering the ID codes, go to Step 6.
The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to use Troubleshooting/inspection Service Points - How to Cope with Intermittent Malfunction ).
 
STEP 5. Recheck for diagnostic trouble code.
Check again if the DTC is set in the WCM.
(1) Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
(2) Check if DTC is set.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is the DTC set?
Replace the engine control module and record the VIN (Refer to GROUP 00 - How To Perform Vehicle Identification Number (VIN) Writing ). Then go to Step 6.
The procedure is complete.
 
STEP 6. Recheck for diagnostic trouble code.
Check again if the DTC is set in the WCM.
(1) Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
(2) Check if DTC is set.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is the DTC set?
Replace the ETACS-ECU.
The procedure is complete.