Diagnostic Procedure

WARNING: This page is about a different car, the 2024 Mazda CX-5. However, it is still accessible from the selected car via links, so may be relevant.

DTC U0401:68 (FRONT BODY CONTROL MODULE) DIAGNOSTIC PROCEDURE

Step	Inspection		Action
1	VERIFY FRONT BODY CONTROL MODULE (FBCM) DTCs AGAIN Clear the DTC for the front body control module (FBCM) using the M-MDS. (See CLEARING DTC [FRONT BODY CONTROL MODULE (FBCM)] .) Switch the ignition ON (engine off or on) and wait for 5s or more. Retrieve the front body control module (FBCM) DTCs using the M-MDS. (See DTC INSPECTION [FRONT BODY CONTROL MODULE (FBCM)] .) Is the same DTC displayed?	Yes	Go to the next step.
1		No	Go to Step 7.
2	VERIFY PCM DTCs Retrieve the PCM DTCs using the M-MDS. (See ON-BOARD DIAGNOSTIC TEST [PCM (VIN Y)] .) (See ON-BOARD DIAGNOSTIC TEST [PCM (VIN L (WITHOUT CYLINDER DEACTIVATION))] .) (See ON-BOARD DIAGNOSTIC TEST [PCM (VIN M (WITH CYLINDER DEACTIVATION))] .) Are any DTCs displayed?	Yes	Repair or replace the malfunctioning part according to the applicable DTC troubleshooting. (See DTC TABLE [PCM (VIN Y)] .) (See DTC TABLE [PCM (VIN L (WITHOUT CYLINDER DEACTIVATION))] .) (See DTC TABLE [PCM (VIN M (WITH CYLINDER DEACTIVATION))] .)
2		No	Go to the next step.
3	INSPECT ENGINE COOLANT TEMPERATURE (ECT) SENSOR Inspect the engine coolant temperature (ECT) sensor. (SEE ENGINE COOLANT TEMPERATURE (ECT) SENSOR INSPECTION [VIN Y] .) (SEE ENGINE COOLANT TEMPERATURE (ECT) SENSOR INSPECTION [VIN L (WITHOUT CYLINDER DEACTIVATION)] .) (SEE ENGINE COOLANT TEMPERATURE (ECT) SENSOR INSPECTION [SKYACTIV-G (WITHOUT EGR COOLER)] .) (SEE ENGINE COOLANT TEMPERATURE (ECT) SENSOR INSPECTION [SKYACTIV-G (WITH EGR COOLER)] .) Is the engine coolant temperature (ECT) sensor normal?	Yes	Go to the next step.
3		No	Replace the engine coolant temperature (ECT) sensor, then go to Step 6. (See ENGINE COOLANT TEMPERATURE (ECT) SENSOR REMOVAL/INSTALLATION [VIN Y] .) (See ENGINE COOLANT TEMPERATURE (ECT) SENSOR REMOVAL/INSTALLATION [VIN L (WITHOUT CYLINDER DEACTIVATION)] .) (See ENGINE COOLANT TEMPERATURE (ECT) SENSOR REMOVAL/INSTALLATION [VIN M (WITH CYLINDER DEACTIVATION)] .)
4	INSPECT AMBIENT TEMPERATURE SENSOR Inspect the ambient temperature sensor. (See AMBIENT TEMPERATURE SENSOR INSPECTION [FULL-AUTO AIR CONDITIONER] .) (SEE AMBIENT TEMPERATURE SENSOR INSPECTION [MANUAL AIR CONDITIONER] .) Is the ambient temperature sensor normal?	Yes	Go to the next step.
4		No	Replace the ambient temperature sensor, then go to Step 6. (See AMBIENT TEMPERATURE SENSOR REMOVAL/INSTALLATION [FULL-AUTO AIR CONDITIONER] .) (See AMBIENT TEMPERATURE SENSOR REMOVAL/INSTALLATION [MANUAL AIR CONDITIONER] .)
5	VERIFY IF MALFUNCTIONING LOCATION IS PCM DEPENDING ON REPEATABILITY Clear the DTC for the front body control module (FBCM) using the M-MDS. (See CLEARING DTC [FRONT BODY CONTROL MODULE (FBCM)] .) Switch the ignition ON (engine off or on) and wait for 5s or more. Retrieve the front body control module (FBCM) DTCs using the M-MDS. (See DTC INSPECTION [FRONT BODY CONTROL MODULE (FBCM)] .) Is the same DTC displayed?	Yes	Replace the PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION [VIN Y] .) (See PCM REMOVAL/INSTALLATION [VIN L (WITHOUT CYLINDER DEACTIVATION)] .) (See PCM REMOVAL/INSTALLATION [VIN M (WITH CYLINDER DEACTIVATION)] .)
5		No	Go to Step 7.
6	VERIFY THAT REPAIRS HAVE BEEN COMPLETED Clear the DTC for the front body control module (FBCM) using the M-MDS. (See CLEARING DTC [FRONT BODY CONTROL MODULE (FBCM)] .) Switch the ignition ON (engine off or on) and wait for 5s or more. Retrieve the front body control module (FBCM) DTCs using the M-MDS. (See DTC INSPECTION [FRONT BODY CONTROL MODULE (FBCM)] .) Is the same DTC displayed?	Yes	Repeat the inspection from Step 1. If the malfunction recurs, replace the front body control module (FBCM). (See FRONT BODY CONTROL MODULE (FBCM) REMOVAL/INSTALLATION .) Go to the next step.
6		No	Go to the next step.
7	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 [FRONT BODY CONTROL MODULE (FBCM)] .)
7		No	DTC troubleshooting completed.