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DTC P0421:00 [PCM (SKYACTIV-G 2.0)]

NOTE:

  • To determine the malfunctioning part, proceed with the diagnostics from "Function Inspection Using M-MDS".

Details On DTCs

DESCRIPTION

Catalytic converter system

DETECTION CONDITION

Determination conditions

  • The PCM detects that the HO2S output fluctuates from lean to rich in a short amount of time at specified times continuously after recovery from fuel cut control.

Preconditions

  • Catalytic converter (WU-TWC) is activated sufficiently.

  • HO2S is activated sufficiently.

  • The following DTCs are not detected:

    • Misfire: P0300:00, P0301:00, P0302:00, P0303:00, P0304:00

    • Fuel injection correction: P0171:00, P0172:00, P2096:00, P2097:00

    • A/F sensor: P0130:00, P0131:00, P0132:00, P0133:00, P0134:00, P064D:00, P2237:00, P2243:00, P2251:00

    • HO2S: P0137:00, P0138:00, P013A:00, P0140:00

    • A/F sensor heater: P0031:00, P0032:00

    • HO2S heater: P0037:00, P0038:00

Drive cycle

  • 1 (U.S.A.)

  • 2 (except U.S.A.)

Self test type

  • CMDTC self test

Sensor used

  • A/F sensor, HO2S

FAIL-SAFE FUNCTION

  • Not applicable

VEHICLE STATUS WHEN DTCs ARE OUTPUT

  • Illuminates check engine light.

POSSIBLE CAUSE

  • HO2S malfunction

    • HO2S loose

  • A/F sensor malfunction

    • A/F sensor loose

    • Exhaust system leakage

    • A/F sensor deterioration

  • WU-TWC deterioration or malfunction

  • PCM malfunction

System Wiring Diagram

  • Not applicable

Function Explanation (DTC Detection Outline)

  • The PCM monitors the oxygen storage amount proportional to the catalytic converter purification characteristic.

  • The PCM starts to monitor after recovery (fuel injection starts) from fuel cut control during deceleration.

  • The PCM temporarily changes the target air/fuel ratio to rich at recovery from fuel cut control, and detects the response time until the HO2S output signal outputs the voltage on the rich side.

  • If the catalytic converter purification characteristic deteriorates, the amount of time until the HO2S detects the voltage on the rich side is shorter compared to the normal purification characteristic as shown in the figure.

  • The PCM detects a catalytic converter malfunction using this characteristic.

Repeatability Verification Procedure

  • Start the engine and leave it idling for 1 min.

  • Drive the vehicle normally for 15 min. After that, shift to 3rd gear and maintain the vehicle speed at approx. 40 km/h {25 mph}.

  • Accelerate the vehicle to 60 km/h {37 mph} while in 3rd gear.

  • Release the accelerator pedal and decelerate the vehicle to 40 km/h {25 mph}.

  • Accelerate the vehicle to 60 km/h {37 mph} again while in 3rd gear.

  • Drive the vehicle for 20 s at a speed of 50 km/h {31 mph} while in 3rd gear.

  • Repeat Step 4 to 6 operations above 20 times.

    NOTE:

    • Match the engine coolant temperature in the recorded FREEZE FRAME DATA/snapshot data, the vehicle speed, and engine speed values to the best extent possible while driving the vehicle.

  • Try to reproduce the malfunction by driving the vehicle for 5 min based on the values in the FREEZE FRAME DATA/snapshot data.

PID Item/Simulation Item Used In Diagnosis

PID/DATA monitor item table

Item

Definition

Unit

Condition/Specification

O2S11

A/F sensor current

µA

  • Idle (after warm up): ???59 µA (ECT is 92 °C {198 °F})

  • Deceleration fuel cut (accelerator pedal released from engine speed of 4,000 rpm or more): Approx. 3.48 mA (ECT is 92 °C {198 °F})

O2S12

HO2S voltage

V

  • Idle (after warm up): 0???1.0 V (ECT is 91 °C {196 °F})

  • Deceleration fuel cut (accelerator pedal released from engine speed of 4,000 rpm or more): Approx. 0 V (ECT is 92 °C {198 °F})

Function Inspection Using M-MDS

STEP

INSPECTION

RESULTS

ACTION

1

 PURPOSE: 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.

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 [PCM (SKYACTIV-G 2.0)].)

3

 PURPOSE: RECORD FREEZE FRAME DATA/SNAPSHOT DATA AND DIAGNOSTIC MONITORING TEST RESULTS TO UTILIZE WITH REPEATABILITY VERIFICATION

NOTE:

  • Recording can be facilitated using the screen capture function of the PC.

  • Record the FREEZE FRAME DATA/snapshot data and DIAGNOSTIC MONITORING TEST RESULTS (catalyst related) on the repair order.

???

Go to the next step.

4

 PURPOSE: VERIFY RELATED PENDING CODE AND/OR DTC

Yes

Go to the applicable PENDING CODE or DTC inspection.

(See DTC TABLE [PCM (SKYACTIV-G 2.0)].)

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 ON-BOARD DIAGNOSTIC TEST [PCM (SKYACTIV-G 2.0)].)

    • O2S11

    • O2S12

  • 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?

    • O2S11: 0.25 mA or more

    • O2S12: 0.3 V or less

Yes

Go to the troubleshooting procedure to perform the procedure from Step 3.

No

Go to the next step.

6

 INSPECT RELATED SENSOR WIRING HARNESS AND CONNECTOR

Yes

Inspect the related wiring harness and connector.

  • Repair or replace the malfunctioning part.

Go to the troubleshooting procedure to perform the procedure from Step 8.

No

Go to the troubleshooting procedure to perform the procedure from Step 1.

Troubleshooting Diagnostic Procedure

    Intention of troubleshooting procedure

  • Step 1???2

    • Perform inspection of HO2S and A/F sensor signal related parts.

  • Step 3???7

    • Perform inspection of each separate part.

  • Step 8???9

    • Verify that the primary malfunction is resolved and there are no other malfunctions.

STEP

INSPECTION

RESULTS

ACTION

1

 PURPOSE: INSPECT INSTALLATION OF HO2S

  • Inspect installation of HO2S.

  • Is the HO2S installed securely?

Yes

Go to the next step.

No

Retighten the HO2S, then go to Step 8.

(See HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)

2

 PURPOSE: INSPECT INSTALLATION OF A/F SENSOR

  • Inspect installation of A/F sensor.

  • Is the A/F sensor installed securely?

Yes

Replace the A/F sensor and/or HO2S, then go to Step 8.

(See AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)

(See HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)

No

Retighten the A/F sensor, then go to Step 8.

(See AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)

3

 PURPOSE: INSPECT INSTALLATION OF HO2S

  • Inspect installation of HO2S.

  • Is the HO2S installed securely?

Yes

Go to the next step.

No

Retighten the HO2S, then go to Step 8.

(See HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)

4

 PURPOSE: INSPECT INSTALLATION OF A/F SENSOR

  • Inspect installation of A/F sensor.

  • Is the A/F sensor installed securely?

Yes

Go to the next step.

No

Retighten the A/F sensor, then go to Step 8.

(See AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)

5

 PURPOSE: INSPECT EXHAUST SYSTEM FOR LEAKAGE

  • Visually inspect for exhaust gas leakage from the exhaust system.

  • Is there any malfunction?

Yes

Repair or replace the malfunctioning part according to the inspection results, then go to Step 8.

No

Go to the next step.

6

 PURPOSE: VERIFY IF OTHER DTCs ARE DISPLAYED

Yes

Go to the applicable PENDING CODE or DTC inspection.

(See DTC TABLE [PCM (SKYACTIV-G 2.0)].)

Go to the next step.

No

Go to the next step.

7

 PURPOSE: VERIFY CATALYTIC CONVERTER MALFUNCTION

Yes

Replace the WU-TWC, then go to the next step.

(See EXHAUST SYSTEM REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)

No

DTC troubleshooting completed.

8

 PURPOSE: VERIFICATION OF VEHICLE REPAIR COMPLETION

Yes

Repeat the inspection from Step 1.

Go to the next step.

No

Go to the next step.

9

 PURPOSE: VERIFY IF THERE IS ANY OTHER MALFUNCTION

  • Is any other DTC or pending code stored?

Yes

Go to the applicable DTC inspection.

(See DTC TABLE [PCM (SKYACTIV-G 2.0)].)

No

DTC troubleshooting completed.
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Free to use workshop manual for your 2015+ Mk4 'ND' Mazda MX-5

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