LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Mazda >> 2020 >> CX-30 Select, AWD >> Repair and Diagnosis >> Engine Performance >> System >> On-Board Diagnostic - Engine Control System (2 Of 4) >> DTC P0421-00: Catalytic Converter System (Us) >> Function Inspection Using M-MDS
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Function Inspection Using M-MDS

DIAGNOSTIC PROCEDURE - FUNCTION INSPECTION USING M-MDS

Step Inspection Results Action
1 PURPOSE: VERIFY RELATED REPAIR INFORMATION OR SERVICE INFORMATION AVAILABILITY
  • Verify related Service Bulletins, on-line repair information, or Service Information availability.
  • Is any related Information available?
 Yes Perform repair or diagnosis according to the available information.
  • If the vehicle is not repaired, go to the next step.
No Go to the next step.
2 PURPOSE: IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA
  • Is the DTC P0421:00 on freeze frame data?
 Yes Go to the next step.
No Go to the troubleshooting procedure for DTC on freeze frame data.
(See DTC TABLE (US) .)
3 PURPOSE: RECORD VEHICLE STATUS WHEN DTC WAS DETECTED TO UTILIZE WITH REPEATABILITY VERIFICATION
  • Record the freeze frame data/snapshot data and diagnostic monitoring test results (catalyst related).
    NOTE:
    • Recording can be facilitated using the screen capture function of the PC.
 - Go to the next step.
4 PURPOSE: INSPECT FOR OTHER RELATED DTCs
  • Perform the DTC inspection for the PCM. (See DTC INSPECTION .)
  • Are any other DTCs displayed?
 Yes Repair the malfunctioning location according to the applicable DTC troubleshooting.
(See DTC TABLE (US) .)
Go to the next step.
No Go to the next step.
5 PURPOSE: VERIFY A/F SENSOR AND HO2S INPUT SIGNAL
  • Start the engine and warm it up completely.
  • Access the following PIDs using the M-MDS: (See PID/DATA MONITOR INSPECTION .)
    • A/F_SEN_CUR
      • HO2S_OUT_VOLT
  • Drive the vehicle under the following conditions.
    WARNING:
    • When the M-MDS is used to observe monitor system status while driving, be sure to have another technician with you, or record the data in the M-MDS using the PID/DATA MONITOR AND RECORD capturing function and inspect later.
      • While performing this step, always operate the vehicle in a safe and lawful manner.
        • After increasing the engine speed to 3, 000 rpm, decelerate using engine braking.
    • Is the displayed PID value as follows?
      • A/F_SEN_CUR: 0.25 mA or more
        • HO2S_OUT_VOLT: 0.3 V or less
 Yes Go to Troubleshooting Diagnostic Procedure to perform the procedure from Step 3.
No Go to the next step.
6 PURPOSE: VERIFY CONNECTOR CONNECTIONS
  • Access the following PIDs using the M-MDS: (See PID/DATA MONITOR INSPECTION .)
    • A/F_SEN_CUR
      • HO2S_OUT_VOLT
  • Does the PID value fluctuate when the following connectors are shaken?
    • A/F sensor
    • HO2S
      • PCM
 Yes Repair or replace the applicable wiring harness or connector parts.
Go to Troubleshooting Diagnostic Procedure to perform the repair completion verification.
No Go to Troubleshooting Diagnostic Procedure to perform the procedure from Step 1.
scientia non olet · About LEMON Manuals