Diagnostic Procedure

WARNING: This page is about a different car, the 2017 Mazda 3. However, it is still accessible from the selected car via links, so may be relevant.

DTC U0401:68 (I-ELOOP) - DIAGNOSTIC PROCEDURE

STEP	INSPECTION		ACTION
1	VERIFY RELATED REPAIR INFORMATION AVAILABILITY Verify related Service Bulletins and/or on-line repair information availability. Is any related repair information available?	Yes	Perform repair or diagnosis according to the available repair information. If the vehicle is not repaired, go to the next step.
1		No	Go to the next step.
2	VERIFY PCM DTCs Switch the ignition off, then ON (engine off). Retrieve the PCM DTCs using the M-MDS. (See ON-BOARD DIAGNOSTIC TEST [PCM (SKYACTIV-G 2.0, SKYACTIV-G 2.5)] .) Are any DTCs present?	Yes	Repair or replace the malfunctioning part according to the applicable DTC troubleshooting. (See DTC TABLE [PCM (SKYACTIV-G 2.0, SKYACTIV-G 2.5)] .)
2		No	Go to the next step.
3	CONFIRM FRONT BODY CONTROL MODULE (FBCM) DTC Perform the front body control module (FBCM) DTC inspection using the M-MDS. (See DTC INSPECTION [FRONT BODY CONTROL MODULE (FBCM)] .) Are any DTCs present?	Yes	Repair or replace the malfunctioning part according to the applicable DTC troubleshooting. (See DTC TABLE [FRONT BODY CONTROL MODULE (FBCM)] .)
3		No	Go to the next step.
4	CONFIRM INSTRUMENT CLUSTER DTC Perform the instrument cluster DTC inspection using the M-MDS. (See DTC INSPECTION [INSTRUMENT CLUSTER] .) Are any DTCs present?	Yes	Repair or replace the malfunctioning part according to the applicable DTC troubleshooting. (See DTC TABLE [INSTRUMENT CLUSTER] .)
4		No	Go to the next step.
5	INSPECT DC-DC CONVERTER CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION [SKYACTIV-G 2.0, SKYACTIV-G 2.5] .) Remove the service plug. (See SERVICE PLUG DISCONNECTION/CONNECTION [i-ELOOP] .) Disconnect the DC-DC converter connector. Inspect for poor connection (such as damaged/pulled-out pins, corrosion). Is there any malfunction?	Yes	Repair or replace the connector and/or terminals, then go to Step 7.
5		No	Go to the next step.
6	INSPECT PCM CONNECTOR CONDITION Disconnect the PCM connector. Inspect for poor connection (such as damaged/pulled-out pins, corrosion). Is there any malfunction?	Yes	Repair or replace the connector and/or terminals, then go to the next step.
6		No	CAN communication line can be considered the cause. Refer to the wiring diagram and verify whether or not there is a common connector between the following terminals: PCM terminal 2AK-DC-DC converter terminal 1A PCM terminal 2AL-DC-DC converter terminal 1C If there is a common connector: Determine the malfunctioning part by inspecting the common connector and the terminal for corrosion, damage, or pin disconnection, and the common wiring harness for a malfunction. Repair or replace the malfunctioning part. If there is no common connector: Repair or replace the wiring harness. If the malfunction recurs, replace the DCDC converter. (See DC-DC CONVERTER REMOVAL/INSTALLATION [i-ELOOP] .) Go to the next step.
7	VERIFY DTC TROUBLESHOOTING COMPLETED Always reconnect all disconnected connectors. Reconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION [SKYACTIV-G 2.0, SKYACTIV-G 2.5] .) Reinstall the service plug. (See SERVICE PLUG DISCONNECTION/CONNECTION [i-ELOOP] .) Clear the DTC for the DC-DC converter using the M-MDS. (See CLEARING DTC [i-ELOOP] .) Switch the ignition off. Switch the ignition ON (engine off) and wait for 5 s or more. Retrieve the DC-DC converter DTCs using the M-MDS. (See DTC INSPECTION [i-ELOOP] .) Is the same DTC present?	Yes	Repeat the inspection from Step 1. If the malfunction recurs, replace the PCM. (See PCM REMOVAL/INSTALLATION [SKYACTIV-G 2.0, SKYACTIV-G 2.5] .) Go to the next step.
7		No	Go to the next step.
8	VERIFY IF OTHER DTCs DISPLAYED Are any other DTCs displayed?	Yes	Repair or replace the malfunctioning part according to the applicable DTC troubleshooting. (See DTC TABLE [i-ELOOP] .)
8		No	DTC troubleshooting completed.