Mazda MPV 2003, Engine light on, code P0421 - warm up catalyst efficiency below threshold bank 1

code p 0421 refers to warm up cat converter bank 1--efficiency below threshold ===causes ---cat converter---wiring---HO2S 2
( heated oxygen sensor)
code p 0431 refers to warm up cat conveter bank 2--efficiency below threshold === causes cat converter --- wiring---HO2S 2
as the same HO2S appears in the cause of the fault I would be inclined to change it first
the HO2sS sensor is the one in the exhaust manifold or before the cat converter
and 2 is in the front bank of a V engine
use the special socket when removing/ replacing these sensors as an incorrect tool is the main reason for wire failures on the sensors

Error Code: P0421
Description:
Warm Up Catalytic Converter, Bank 1 - Efficiency Below Threshold
Possible Cause:
Warm Up Catalyst Bank 1 faulty.
Possible Solutions:
Check Warm Up Catalyst Bank 1 - Set Readiness.
Replace Warm Up Catalyst Bank 1.

P0305 - Cylinder number 5 misfire detected.
Probable faults and reasons:
Igniter no. 5 defective.
Ignition system malfunction.
Spark plug is short or its air too wide. (0.9 - 1.1 mm)
Weak compression.
Valve clearance less than recommended.
Engine valves and seats defective.
Fuel pump pressure too high.
P0421 - Warm up catalytic efficiency is below threshold (Bank 1)
Probable faults and reasons:
Catalytic converter.
Heated oxygen Bank 1.sensor 1, 2.
P1818 - Manufacturer specific code.

P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)
____________-
Can Clip Renault

Have the catalytic converter and your O2 sensor checked.

EXHAUST RELATED ERROR CODES

There are 711 possible PO generic DTC error codes. Only 7 of the 711 codes are exhaust related.

PO401: Insufficient EGR Flow

PO402: Exhaust Gas Recirculation (EGR) Excessive Flow Detected

PO410: Secondary Air Injection System Malfunction

PO420: Catalyst System Efficiency Below Threshold (Bank 1)

PO421: Warm-Up Catalyst Efficiency Below Threshold (Bank 1)

PO430: Catalyst System Efficiency Below Threshold (Bank 2)

PO431: Warm-Up Catalyst Efficiency Below Threshold (Bank 2)

THINGS TO ASK YOURSELF OR YOUR CUSTOMER

Have there been any driveability or performance issues with the vehicle, have there been any recent repairs or tune-up work performed, if so was the check engine light reset and were the codes recorded on previous repair orders.

Do not rely on scan tool data alone. In most applications, the customer will have the check engine light reset prior to repair. If the original cause of converter failure is intermittent, only the catalyst failure code may show up

P0421: Warm Up Catalyst Efficiency Below Threshold (Bank 1).

This could apear because of a bad O2 sensor on the catalytic converter on bank 1.

Or The catalytic converter is no longer functioning properly.

Hope this helps you. Good luck bro

CODE P0421. DEFINITION-CATALYST EFFICIENCY LOW-BANK 1. EXPLANATION-THE OXYGEN SENSORS MONITOR THE CATALYTIC CONVERTERS ABILITY TO STORE OXYGEN. PROBLEM CAUSES- 1. CATALYTIC CONVERTER DEFECTIVE (FAILURE POSSIBLY DUE TO #2,3, OR 4) 2. ENGINE MISFIRE OR RUNNING CONDITION. 3. LARGE VACCUM LEAK 4. ENGINE OIL LEAKAGE INTO EXHAUST-VALVE GUIDE SEALS, PISTON RINGS. THE PCM HAS DETERMINED THAT THE WARM UP CATALYST EFFICIENCY FOR BANK 1 IS BELOW TRESHOLD FOR THE CURRENT ENGINE OPERATING CONDITION. (BANK 1 IDENTIFIES THE LOCATION OF CYLINDER #1, WHILE BANK 2 IDENTIFIES THE CYLINDERS ON THE OPPOSITE BANK).

replace O2 sensors, or your Catalytic Converter.

po421 warm up catalyst efficiency below threshhold bank 1, 431 same on bank 2..

P0327 Knock Sensor 1 Circuit Low Bank 1 or Single Sensor
P0431 Warm Up Catalyst Efficiency Below Threshold Bank 2