P0421 code bank 1 warm-up efficiency below limit

P0421 is a diagnostic trouble code (DTC) for "Warm Up Catalyst Efficiency Below Threshold (Bank 1)". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation.

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)
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Can Clip Renault

Hi there:DTC P0421 - Warm Up Catalyst Efficiency Below Threshold (Bank 1)


Basically this means that the oxygen sensor downstream of the catalytic converter on bank 1 is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.


You will likely not notice any drivability problems, although there may be symptoms. The code may be more likely to occur after the engine has had numerous cold starts in the past 1-2 days.



A code P0421 may mean that one or more of the following has happened:



The catalytic converter is no longer functioning properly
An oxygen sensor is not reading (functioning) properly
A sparkplug is fouled up


Possible Solutions: Measure the voltage at the oxygen sensor on Bank 1 (the rear sensor, or the sensor after the converter). In fact, it would be a good idea to test each oxygen O2 sensor while you're at it.


One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.


Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

Hi there,

P0421 = Warm Up Catalyst Efficiency Below Threshold (Bank 1)

This means the HO2 (Oxygen) Sensor downstream of the catalytic converter on bank 1, is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

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..

If you have more than 60K miles start by replacing the Oxygen sensor(s) that is(are) installed after the catalytic converter(s). 
P0421: Warm up catalyst efficiency below threshold. This code means that the computer is detecting the catalyst not warming up to full function quickly enough based on information from the post cat O2 sensor. 

Good luck and hope this helps.