P0421 Mitsubishi Code - Warm Up Catalyst Efficiency Below Threshold- Cylinders 1-4
Quick Answer
The P0421 diagnostic trouble code (DTC) for Mitsubishi vehicles indicates that the warm-up catalyst efficiency for cylinders 1-4 is below the threshold set by the vehicle's onboard computer. Common causes include Faulty Catalytic Converter: The most common cause of the P0421 code is a malfunctioning catalytic converter that is no longer able to efficiently convert harmful emissions, Oxygen Sensor Issues: A faulty oxygen sensor can provide incorrect data to the engine control module, leading to improper air-fuel mixture and inefficient catalytic converter operation, Exhaust Leaks: Leaks in the exhaust system before the catalytic converter can allow unburned fuel to enter the converter, reducing its efficiency. Severity is Moderate - service should be scheduled soon. The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.
- What it means
- P0421 Mitsubishi indicates Warm Up Catalyst Efficiency Below Threshold- Cylinders 1-4.
- Common causes
- Common causes include Faulty Catalytic Converter: The most common cause of the P0421 code is a malfunctioning catalytic converter that is no longer able to efficiently convert harmful emissions, Oxygen Sensor Issues: A faulty oxygen sensor can provide incorrect data to the engine control module, leading to improper air-fuel mixture and inefficient catalytic converter operation, Exhaust Leaks: Leaks in the exhaust system before the catalytic converter can allow unburned fuel to enter the converter, reducing its efficiency.
- Severity
- Moderate - service should be scheduled soon.
- Can I drive?
- The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.
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Code P0421 Mitsubishi Description
The P0421 diagnostic trouble code (DTC) for Mitsubishi vehicles indicates that the warm-up catalyst efficiency for cylinders 1-4 is below the threshold set by the vehicle's onboard computer. This means that the catalytic converter, which is responsible for reducing harmful emissions from the exhaust gases, is not working as efficiently as it should during the warm-up phase of the engine. This can lead to increased emissions and reduced fuel efficiency. If left unaddressed, it can also cause damage to other components of the exhaust system and potentially trigger other DTCs related to emissions control.
Common Causes of P0421 Mitsubishi
- Faulty Catalytic Converter: The most common cause of the P0421 code is a malfunctioning catalytic converter that is no longer able to efficiently convert harmful emissions.
- Oxygen Sensor Issues: A faulty oxygen sensor can provide incorrect data to the engine control module, leading to improper air-fuel mixture and inefficient catalytic converter operation.
- Exhaust Leaks: Leaks in the exhaust system before the catalytic converter can allow unburned fuel to enter the converter, reducing its efficiency.
- Engine Misfires: Continuous engine misfires can lead to an accumulation of unburned fuel in the catalytic converter, causing it to work inefficiently.
Symptoms of P0421 Mitsubishi
- Check Engine Light: The most common symptom associated with the P0421 code is the illumination of the Check Engine Light on the vehicle's dashboard.
- Decreased Fuel Efficiency: A faulty warm-up catalyst can lead to decreased fuel efficiency as the engine may not be burning fuel as efficiently as it should.
- Rough Idling: The engine may experience rough idling or hesitation during acceleration due to the inefficient operation of the catalytic converter.
- Failed Emissions Test: If the catalytic converter is not working properly, the vehicle may fail an emissions test due to increased emissions.
How to Fix P0421 Mitsubishi
- Diagnose the Issue: Use a diagnostic scanner to retrieve the specific DTC and pinpoint the exact cause of the P0421 code.
- Inspect and Replace Oxygen Sensors: Check the oxygen sensors for proper operation and replace any faulty sensors.
- Check for Exhaust Leaks: Inspect the exhaust system for any leaks and repair or replace damaged components.
- Replace Catalytic Converter: If the catalytic converter is determined to be faulty, it will need to be replaced with a new one.
- Clear DTCs and Test Drive: After completing the repairs, clear the DTCs from the vehicle's memory and test drive to ensure the issue has been resolved.
Cost to Fix P0421 Mitsubishi
The cost of repairing a P0421 code can vary depending on the specific cause of the issue and the type of repair needed. Replacing an oxygen sensor can cost between $100 and $300, while replacing a catalytic converter can range from $500 to $2,500. Labor costs can add an additional $100 to $500, depending on the complexity of the repair. It is advisable to consult with a trusted mechanic or auto repair shop for a more accurate estimate based on the specific vehicle make and model.
Tech Notes for P0421 Mitsubishi
There is a factory service recall for the following Mitsubishi Models:
2002 Mitsubishi Lancer
2003 Mitsubishi Lancer
2004 Mitsubishi Lancer
2005 Mitsubishi Lancer
2002−2005 Mitsubishi Lancer Factory Service Recall OBDII Code P0421
When is the Code Detected?
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Frequently Asked Questions about P0421 Mitsubishi Code
1. What are the common symptoms of OBDII code P0421 in a Mitsubishi related to warm-up catalyst efficiency below threshold on cylinders 1-4?
The common symptoms include decreased fuel efficiency, reduced engine performance, and the illumination of the check engine light.
2. What are the potential causes of OBDII code P0421 in a Mitsubishi, indicating warm-up catalyst efficiency below threshold on cylinders 1-4?
Possible causes include a faulty catalytic converter, oxygen sensor issues, exhaust system leaks, or engine misfires.
3. How can I diagnose the OBDII code P0421 in my Mitsubishi for warm-up catalyst efficiency below threshold on cylinders 1-4?
Diagnosis typically involves using an OBDII scanner to retrieve the code, checking for any additional related codes, inspecting the catalytic converter, and testing the oxygen sensors.
4. Can driving habits contribute to triggering OBDII code P0421 in a Mitsubishi for warm-up catalyst efficiency below threshold on cylinders 1-4?
Yes, frequent short trips or driving with a heavy foot can potentially lead to incomplete combustion, causing the catalytic converter to operate less efficiently and triggering the code.
5. What are some repair tips for addressing OBDII code P0421 in a Mitsubishi due to warm-up catalyst efficiency below threshold on cylinders 1-4?
Repair tips may include replacing the catalytic converter, repairing any exhaust leaks, ensuring proper oxygen sensor function, and addressing any underlying engine misfire issues.
6. Is it safe to continue driving my Mitsubishi with OBDII code P0421 indicating warm-up catalyst efficiency below threshold on cylinders 1-4?
While the vehicle may still be operable, it is recommended to address the issue promptly to prevent further damage to the engine components and ensure optimal vehicle performance.
7. Will resetting the OBDII code P0421 in my Mitsubishi fix the issue of warm-up catalyst efficiency below threshold on cylinders 1-4?
Resetting the code may temporarily turn off the check engine light, but it will not fix the underlying problem causing the code. It is crucial to diagnose and address the root cause of the issue.
8. Can a clogged air filter contribute to triggering OBDII code P0421 in a Mitsubishi for warm-up catalyst efficiency below threshold on cylinders 1-4?
Yes, a clogged air filter can disrupt the air-fuel mixture ratio, potentially leading to inefficient combustion and triggering the code.
9. How can I prevent OBDII code P0421 from recurring in my Mitsubishi after repair for warm-up catalyst efficiency below threshold on cylinders 1-4?
Regular maintenance, such as timely oil changes, replacing air filters, and driving conservatively, can help prevent the recurrence of the code.
10. Are there any specific Mitsubishi models known to be more susceptible to OBDII code P0421 indicating warm-up catalyst efficiency below threshold on cylinders 1-4?
While any Mitsubishi model can potentially experience this issue, certain models with higher mileage or older catalytic converters may be more prone to triggering the code.
Discuss the causes and fixes for P0421 Mitsubishi OBDII Code
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how much does it cost to replace and install a warm up catalyst effiecency for bank 1 on a 1999 mit galant es
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Prices varies from store to store. A catalytic converter could be very expensive, you should have a tech inspect the one on your car before replacing it.
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I have a 2001 Galant ES and I received codes P0135 and P0421. I replaced Bank 1 O2 sensor for $70 (spare part cost, I bought BOSCH) I replaced this sensor myself so it cost me $70. After replacing this sensor I am still seeing P0421 after driving for few miles. I am thinking of Bank 2 sensor replacing or going to a technician. :(
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P0135: https://www.autocodes.com/p01...
This code was definitely the O2 sensor Bank 1, so you did correctly by changing the sensor.
For your 2001 Galant ES, the P0421 means that there is a problem the catalytic converter. Unfortunately you may have to replaced the catalytic converter to fix the problem.
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so far the best (411)information i re call ,i have a 2000 mitsubishi montero sport ls
and the check eng light is on ,as far as going from drivwe too reverse it it almost trups the rear tires hard shift ,but if i go from park too reverse there is NO PROBLEN ?
THE CODES I HAVE CURRENTLY ARE
PO421
PO705
ALSO IM DUE FOR A VALVE COVER GASKET JOB
SOME TIMES THERE I SEE LITTLE SMOKE COMMING FROM REAR TAIL PIPE
CAN SOME ONE GIVE THERE REPLY THANKS ROBERT OF WEST COVINA,,THIS WAS SOLD FROM CENTRAL AUTO SALES IN ELMONTE I SHOULD HAVE WENT W/THE 1ST CAR LOT THERE WAS A MULTIBLE PROBLEMS W/IT THANKS GABRIEAL PACAL -
You may have a problem with the O2 sensor or the catalytic converter, more than likely the problem is the catalytic converter, but you should try erasing the codes first and try fixing the code that comes back first.
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which converter has to be replace? three way catalytic converter on the front or catalytic converter under the car?
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What model and year is your Mitsubishi? Usually is the one between the front and rear oxygen (O2) sensors.
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I have a 2005 mitsubishi galant n having codes p0421 &p0431. Could that be mean I need to change the catalytic converter?
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If there are no drivability or engine performance problem, the it's very likely that the problem is the catalytic converter.
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I am experiencing PO421 and 423. I am assuming that I am going to have to replace my cati. If I do so, will I need to buy new O2 sensors as well?
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Good question, but all depends on many factors, mileage, age of your vehicle the way you drive and type of gas you use. Most O2 sensor do deteriorate with time. If you vehicle it's old and high mileage, and you can afford to buy sensor, then you should change them to aviod paying again later for labor.
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Hello I have a 2002 Mitsubishi Galant 4 cylinder, I recently had a diagnostic and code P0421 showed up. There were no other codes so I need a clearer understanding if what steps I need to do now to take care of the problem. I know I also need motor mounts. Which is more important and which should I put off til I get the money? Thank you
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Depends how bad are the mounts and the catalytic converter.
If the catalytic converter is bad your vehicle won't be able to pass the emissions test (smog test), also if the catalytic is "really" bad you may experience some engine performance problem, e.g. no engine power.
If the mounts are bad you may experience some vibration, if the mounts is really bad you could experience shifting problems, vibrations, and other problems.
Your mechanic is the best position to recommend what you should do now and what can wait.
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So my 2002 Mitsubishi Lancer Oz rally failed an emissions test. My service engine light was on and it is the P0421 code. The car has less than 100k miles. I would think it is more likely o2 sensors rather than a catalytic converter with less than 100k right? So would I pass the emissions test if I reset the code?
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More than likely is the catalytic converter, it's not just the mileage, there are other things that could damage the catalytic converter, for example: fuel quality, maintenance, driving conditions, temperature.
Before replacing any parts, try the following: Use high octane gas for a couple of days (or more), clear the code, drive it for one more day and then try the test again. You can't just clear the code and test.
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I ran a scan on my 2001 Mitsubishi eclipse and the code is P0421 and P0425. What does it mean? Do I need a new Cythlic converter?
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Yes for the P0421, it's very likely that you need a catalytic converter.
I checked the factory service manual and I can't find any information for the P0425 code.
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Can I just add an octane booster and drive around for a few days then do as you suggested?
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Hi there - 02' Misubishi OZ Rally red'd service fail code P0421 - with no check engine light - fail OBDII and FAIL OBD Bulb Check - does this mean i will need new cati and o2 sensors? 130K - well maintenanced -
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Hey there- I have 2004 Mitsubishi Lancer and it's had the P0421 code for 3 years. First time I changed the first o2 sensor, and preformed ECM recall and it got rid of code and passed smog. This past month I changed both and still didn't pass. Had to replace exhaust manifold and now code gone and passed. Hope that helps.
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Hi, I Have 2003 Mitsubishi Lancer I bought the car when the previous owner didn't have a muffler. Went to go fix it put in a new Flex connector and Muffler. He didn't change the Catalyst Converter next to the engine or underneath the car. When I fixed it that night my engine light turn on. Went to a Auto Zone a week after to get it checked. Show P0421 Warmup Catalyst Efficiency Low (Bank 1). A few days ago just did a oil changed and engine light is still on.
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Hi,
Mine is lancer 02 and I have an OBD tool connected to my laptop run software. I see the code P0421 but along with that the software also shows O2 sensors are normal. Do you think that I am reading software correctly as I saw online information, it seems to me that the tool is not capable of distinguishing these 2 issues of sensor and converter?
And this code comes with the close coupled converter, which is closer to the exhaust I suppose? I see autozone has this http://www.autozone.com/emi...
labeled "Main Catalytic Converter" that I think it's the close coupled. Can you please let me know if any welding or any work that requires unusual tool if the converter I am pointing to is correct?
Thank you very much,
Dave -
The one on AutoZone is an universal catalytic converter and does required welding. Also, you can't use that catalytic converter if you live in California.
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Hello.i have the Mitsubishi ecluos gs 2003 and i didnt pass the test emission..and i have the light service engine soon on so when i went to check it out i found the p0421 warmup catalyst efficiency low bank1 ..and now i dont know what i have to do ?because when i asked for how much for change it they said is expencive and the car now make a noise ...any solution ?
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Unfortunately, as far as, the only solution is replace the catalytic converter.
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2004 Galant 2.4L ES with P0421 code, O2 sensor changed and didn't fix. Which catalytic converter needs to be changed? Manifold, downstream or both?
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Hello, I have a 99 Mitsubishi Galant with 2.4 engine and I'm getting P0421 code pending on the OBD II reader but without the check engine light. Would that mean one or both of the 02 sensors are bad before the catalytic converter? I can reset the code, drive and a pending code will reappear but still no check engine light. Please help!
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More than likely means that the catalytic converter itself is failing and not the sensors. If the problem are the sensors, the it will trigger the O2 sensors codes. But before changing the catalytic converter, try using high octane gas for a couple of weeks, and if possible, add a fuel additive.
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Hello! My car has error codes P0335 and P0421. I was told it may either be the catalytic converters or 02 sensors. Can you give me some insight please? I have a 2006 Mitsubishi Galant
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P0335 is for the Crankshaft Position Sensor and could be a different problem. For the P0421 code unfortunately could be either one, there are some test that needs to be run to determine exactly what the problem is, but 98% of the times is the Catalytic Converter
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I was driving and heard a pop and smelled burning. After this happened i told my husband and when he drive it up street it was no longer stalling like before but still have light on. So would that pop have been 02 sensor?
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No, there is no noise when the O2 sensor fail, but the Catalytic converter could make some rattle noise.
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2002 lancer oz rally.
Passed smog, had service light on, with p0421. Just the sensor?
Thanks! -
Which Sensor. Since already passed smog, try using high octane gas for a couple of weeks, if the problem persists you may have to replace the catalytic converter.
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2007 Galant Ralliart
Service engine soon light on. I'm getting a P0421 code (only code) but I've been using regular octane gas for the past few months(The car does say use premium only oops). Should going back to premium gas fix this error code? If so how long after switching back to premium will the light go back off. I put a tank of premium with octane booster in the car and reset the service engine light but the light turned back on about 25mi after resetting the code. If I in fact do need to replace the catalytic converter which one do I need to replace? Thanks for any help!
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Unfortunately there is no way to know how long it will take to clear the light if you start using high octane gas. Also, changing the fuel does not guaranty the problem will get fix. it all depends how bad is the catalytic converter. I recommend using high octane gas for about a month, if the code keeps coming back, then you may have to replace the catalytic converter. The catalytic converter is part of the exhaust manifold and bank 1 is the right side.
Click here to enlarge image -
I change my O2 sensor every year I have to get my car inspected. It never seems to last the full 2 years. I have a 2003 Mitsubishi Lancer with P0421 code. I see above there is a factory recall for this problem so I will look into that. The catalytic converter is suppose to last a lifetime if the engine is running properly (not dumping unburnt fuel into it). Seems like just changing the catalytic converter is a waste of money if you don't fix the underlying cause.
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What fuel octane and brand are you using? What I have seen often is that the problem is not the vehicle or driver, but the fuel quality.
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Why do I have to wait 'till the motor is warmed up before it works stationairy?
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Could you please elaborate your question? what mode and year is your vehicle?
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Sorry my fault. My car is a Mitsubishi Lancer 2005 Chasisnr:JMYSRCS1A5U001826 Engine; 4G13 MODEL;OSIASRDEL When cold it starts but when I put the car in gear (automatic) the engine stops running. When I leave the care idle with the trottle a little bit high for about 5 to ten minutes it keeps running normal. Thnx for your reply.
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Unfortunately there are many thing that could cause that problem, from low base idel, spark plugs, fuel injector to fuel pump, but if you only have the P0421 code, then there is a chance that the problem is a clogged catalytic converter. Do you have any rattle noises from the exhaust?
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Click here to enlarge imageHi, I have the code P0421 and my OBD reader shows me the following live data. Car is Mitsubishi Lancer 2004, 1.6 litres. The O2 sensor before converter shows reasonable volts (yellow line, averiging at 0,35 - 0,4 volts) but the latter goes from very lean to very rich all the time, except at cold start when it shows very rich all the time. The exhaust does not smell and the car passed exhaust test at May this year.
Does this information say the converter is bad, or is the latter O2 sensor failing (could be clogged or at the end of lifetime)? The car also gives some rough idle the first two minutes when cold starting, but settles very quickly when given a little RPMs. I have resetted the code several times and it does not come back immediately, but maybe after five starts.
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Unfortunately there are many variable than can affect the O2 sensors readings (e.g. engine temperature, engine speed, fuel quality, etc.) and the sample is to small to accurate diagnose the problem. Since you have the P0421 code and it takes some time to come back, after you clear, then either the catalytic converter is just starting to fail or you may have bad gas. I recommend using high octane gas for a couple of weeks and if possible use a fuel additive to clean carbon deposits that may affecting the O2 sensor readings.
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I hav a 01 Eclipse GT and the code came up on last smog check I don’t hav any lose in power no rattle from the cat what would be my next step
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You could clear the code and start by using high octane gas and a fuel additive for a couple of weeks, then check for codes again. If the problem persists then you may have to replace the catalytic converter.
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Hi, I have P0131 and P0421 on my 2006 Mitsubishi Lancer Oz rally 2.0L. It has been ON/OFF since 1-2 years ago, usually it turns on on cold weather, but now it's hot and the codes are still there. I replaced the O2 sensor (upstream before the cat) but that seemed to be hit/miss, sometimes it works, sometimes it doesn't (code shows up). Do you have any clue?
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Yes. They both do. I erased it already a week ago. Today I erased it and will observe again. How do I know if there are any leaks? Just visual inspection? I can't see anything near the upstream O2 sensor. I also took a video of the O2 sensor voltages (Bank 1 & 2), I was wondering if you could take a look at it and see if you can diagnose the cat converter..
Video is here: https://www.youtube.com/wat...
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Btw, I'd like to add that the car runs fine and I use it everyday with no problem. I can reach 50-70 MPH without observing any power issues in the engine.
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My old reply got deleted. But both the codes come back. I deleted them last week and they came back. I deleted them today and will observe it again. I took a video of my O2 sensor voltages (sensor 1 and 2) and found that they seem to follow each other when I throttle the gas pedal. I will put the video link in a separate reply so it's not deleted..
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You can find out if there are exhaust leaks by visual checking the exhaust or by listing for noise from the exhaust.
Unfortunately I'm not able to diagnose the sensor from the video, there are other parameters that needs to be consider (e.g sensor and outside temperature, mileage, age of your vehicle) to proper diagnose the problem.
My best guess is that the catalytic converter is deteriorating and setting the code under certain conditions.
Have to try using high octane gas or catalytic converter cleaner? sometimes that will take care of the problem. -
I haven't tried high octane gas yet. I might try that and the lucas fuel system cleaner. Outside temperature when doing this test was 60-70F if that helps. This is 2006 mitsu lancer oz-rally 75K miles.
I reset the code 3 days ago and it hasn't come up yet. The emission status of the system is ready. So I'm hoping it stays that way.
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Hello Vicente,
2004 mits lancer ES , I had the same code:P0421, 3 years back got it replaced with new Catalytic converter. after 1.5 years again same code is back, since last 6 months i am driving without repair.. I am worried cant spend much on this issue.With your above message, Understand I too can drive my car , No problem.
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2007 eclipse spyder 2.4L
P0431 code came up last september and i replaced the cat converter. Fast forward to the middle of March and now its the P0421 code. I took it to a mechanic and he suggested resetting the code and then driving for a while to see if it came back up. Fast forward two months and at least 300 miles later and the code just came back up (also it appears twice on the reading). Do I need to change the cat again? Or is there probably something else tripping it up? I'm wondering why it took so long to pop back up. Also car feels fine.
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Try using high octane gas and if possible, a fuel additive to clean the cat. If that doesn't work, you must replace the catalytic converter.
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