Diagnostic Procedure

WARNING: This page is about a different car, the 2020 Mazda CX-30. However, it is still accessible from the selected car via links, so may be relevant.

DTC B1258:87 [DASH-ELECTRICAL SUPPLY UNIT (US)] DIAGNOSTIC PROCEDURE

Step	Inspection	Results	Action
1	INSPECT FOR OTHER RELATED DTCs Perform the DTC inspection for the dash-electrical supply unit. (See DTC INSPECTION .) Are any of the following DTCs displayed? U3003:16 U3003:17	Yes	Repair the malfunctioning location according to the applicable DTC troubleshooting. (See DTC TABLE [DASH-ELECTRICAL SUPPLY UNIT (US)] .)
1		No	Go to the next step.
2	INSPECT REAR VENT ACTUATOR CONNECTOR FOR MALFUNCTION Inspect the applicable connector and terminal. (See CONNECTOR INSPECTION .) Are the connector and terminal normal?	Yes	Go to the next step.
2		No	Repair or replace the malfunctioning location and perform the repair completion verification.
3	INSPECT DASH-ELECTRICAL SUPPLY UNIT CONNECTOR FOR MALFUNCTION Inspect the applicable connector and terminal. (See CONNECTOR INSPECTION .) Are the connector and terminal normal?	Yes	Go to the next step.
3		No	Repair or replace the malfunctioning location and perform the repair completion verification.
4	INSPECT REAR VENT ACTUATOR LIN COMMUNICATION LINE FOR SHORT TO GROUND Inspect the applicable circuit for a short to ground. (See CIRCUIT INSPECTION .) Is the circuit normal?	Yes	Go to the next step.
4		No	Repair or replace the malfunctioning location and perform the repair completion verification.
5	INSPECT REAR VENT ACTUATOR LIN COMMUNICATION LINE FOR SHORT TO POWER SUPPLY Inspect the applicable circuit for a short to power supply. (See CIRCUIT INSPECTION .) Is the circuit normal?	Yes	Go to the next step.
5		No	Repair or replace the malfunctioning location and perform the repair completion verification.
6	INSPECT REAR VENT ACTUATOR LIN COMMUNICATION LINE FOR OPEN CIRCUIT Inspect the applicable circuit for open circuit. (See CIRCUIT INSPECTION .) Is the circuit normal?	Yes	Go to the next step.
6		No	Repair or replace the malfunctioning location and perform the repair completion verification.
7	INSPECT REAR VENT ACTUATOR FOR MALFUNCTION DEPENDING ON REPEATABILITY Install/connect the part removed/disconnected during the troubleshooting procedure. Clear the DTC recorded in the memory. (See CLEARING DTC .) Perform the DTC inspection for the dash-electrical supply unit. (See DTC INSPECTION .) Is the same Pending DTC present?	Yes	Refer to the controller area network (CAN) malfunction diagnosis flow to inspect for a CAN communication error. (See CONTROLLER AREA NETWORK (CAN) MALFUNCTION DIAGNOSIS FLOW (US) .) If the CAN communication is normal, replace malfunctioning location and perform the repair completion verification. (See REAR VENT ACTUATOR REMOVAL/INSTALLATION [FULL-AUTO AIR CONDITIONER] .)
7		No	Go to repair completion verification 2.
Repair completion verification 1	VERIFY THAT VEHICLE IS REPAIRED Install/connect the part removed/disconnected during the troubleshooting procedure. Clear the DTC recorded in the memory. (See CLEARING DTC .) Perform the DTC inspection for the dash-electrical supply unit. (See DTC INSPECTION .) Is the same Pending DTC present?	Yes	Refer to the controller area network (CAN) malfunction diagnosis flow to inspect for a CAN communication error. (See CONTROLLER AREA NETWORK (CAN) MALFUNCTION DIAGNOSIS FLOW (US) .) If the CAN communication is normal, perform the diagnosis from Step 1. If the malfunction recurs, replace the dash-electrical supply unit, then go to the next step. (See DASH-ELECTRICAL SUPPLY UNIT REMOVAL/INSTALLATION [FULL-AUTO AIR CONDITIONER (US)] .)
Repair completion verification 1		No	Go to the next step.
Repair completion verification 2	VERIFY IF OTHER DTCs DISPLAYED Perform the DTC inspection. (See DTC INSPECTION .) Are any DTCs displayed?	Yes	Repair the malfunctioning location according to the applicable DTC troubleshooting.
Repair completion verification 2		No	DTC troubleshooting completed.