Traditional gasoline car fault

2004 Volkswagen Passat GLX P0300 and P0421 Error Codes: Causes and Solutions

Hello! I own a 2004 Volkswagen Passat GLX, and the check engine light has come on. A diagnostic scan revealed two trouble codes: P0300 (random misfire) and P0420 (catalyst syste...

2004 Passat | P0300

2004 Mazda6 P0421 Fault Code: Causes and Solutions for Catalytic Converter or Oxygen Sensor Issues

I own a 2004 Mazda6 with an automatic transmission, and I've recently received the P0420 diagnostic trouble code. As someone with limited car knowledge, I'm looking for clear gu...

2004 Mazda 6 | P0421

2002 Audi A4 3.0T P0171 P0421 P0431 Fault Codes: Affordable Repair Solutions

What is the most cost-effective way to diagnose and fix the P0171, P0421, and P0431 fault codes in a 2002 Audi A4 3.0T without spending a large amount of money? These codes indi...

2002 Audi A4 3.0T | P0171

2004 Hyundai Sonata P0401 and P0421: Causes, Fixes, and Next Steps Before Inspection

I've been experiencing a persistent P0400 code on my 2004 Hyundai Sonata for over a year. Recently, the vehicle has developed a new issue — a P0421 code. I'm trying to understan...

04 Sonata | P0401

2003 Hyundai Santa Fe P0401 and P0421 Codes After Timing Belt Replacement at 250,000 Miles

I have a 2003 Hyundai Santa Fe with 250,000 miles and a 4-cylinder engine. Recently, I had the timing belt replaced at a dealership. After returning, I noticed increased engine ...

2003 Santa Fe | P0401

2006 Mazda MX5 1.8L P0421 Fault After Using Terraclean - Cat Clog Suspected

I own a 2006 Mazda MX5 with a 1.8L MXR engine and 5-speed transmission (known as Miata in the US). After performing a Terraclean service, I began receiving a P042-1 diagnostic e...

2006 Mazda MX5 | P0421

2005 Mitsubishi Endeavor LS P0431, P0174, P0421, P0171, P0304, P0431

I have a 2005 Mitsubishi endeavor with the following codes: P0431, P0174, P0421, P0171, P0304, and P0431 and I haven't the faintest idea what any of them mean. I have searched t...

2005 Mitsubishi Endeavor LS | P0171

2002 Audi A6 P0421 and P0352 Fault Codes: Engine Shaking Until Oil Temperature Stabilizes

My 2002 Audi A6 is experiencing noticeable shaking or vibration when under load, which only stops once the engine oil temperature reaches its operating range. The vehicle has tr...

2002 Audi A6 | P0352

2002 Mitsubishi Lancer OZ Rally - P0421 Code Fix & Missing Vacuum Control Valve (California Smog Ready)

I recently acquired a 2002 Mitsubishi Lancer OZ Rally with 240,000 miles. After fixing several previous issues—P0401, P0507, P0441, and a misfire caused by oily spark plugs—I be...

2002 Mitsubishi Lancer OZ Rally | P0421

P0421 and P0300 Codes on 2003 Mazda Protege - O2 Sensor or Catalytic Converter Issue?

Note: This 2003 Mazda Protege has only 50,000 miles and was purchased from a woman who likely rarely drove it above 45 mph. I initially experienced misfiring in one or more cyl...

2003 Mazda Protege | P0300

2004 Eclipse Check Engine Light with Codes P0106, P0108, P0421 and Low Compression in Cylinder 1?

Our daughter's 2004 Dodge Eclipse has been causing significant trouble for over a year. The check engine light first appeared more than a year ago, and despite multiple visits t...

04 Eclipse | P0106

1999 Mazda Protege P0421 OBD2 Code: Causes and Solutions for Catalytic Converter Efficiency Issue

My 1999 Mazda Protege ES with 127,000 miles is currently displaying only the P0421 diagnostic trouble code. I recently replaced the spark plug set and lower radiator hose, and h...

99 Mazda Protege | P0421

2004 Mitsubishi Lancer OZ Rally P0421 Check Engine Light: Cat or Downstream O2 Sensor? How to Diagnose and Fix for Smog Compliance

My 2004 Mitsubishi Lancer OZ Rally passed smog inspection last year, but six months later the check engine light came on. Using an OBD-II scanner, I found fault code P0421 — ind...

2004 Mitsubishi Lancer OZ Rally | P0421

2000 Mazda MPV 2.5L California Model P0421 Fault Code: Which Bank Is the Catalyst Converter and How to Fix It?

I'm trying to identify which bank the catalyst converter is located in for my 2000 Mazda MPV 2.5L California model, specifically regarding OBD-II fault code P0421. Could someone...

2000 mazda MPV | P0421

Mazda Premacy 2001 1840cc P0420 and P0421: Is Catalytic Converter Replacement Necessary? Diagnosing OBD-II Error Codes for Older Vehicles

I own my Mazda Premacy 2001 (1.8L 1840cc) for about 10 years. For many years, I've had the check engine light on due to error codes P0420 and later P0421. At a local garage, the...

Mazda Premacy | P0420

2005 Jeep Wrangler P0421 Code Explanation: What It Means and How to Fix It

My 2005 Jeep Wrangler is showing a P0421 diagnostic trouble code. I want to understand what this code means and what repairs are needed to resolve it. The vehicle has a 4.0L eng...

2005 Jeep | P0421

2001 Audi A6 P0421 and P074-OBD2 Codes: Do I Need to Replace Catalytic Converter and Torque Converter? | Smog Test & Emission Fix

I own a 2001 Audi A6 with approximately 142,222 miles. Recently, my check engine light came on, and the OBD-II scanner detected two trouble codes: P0421 and P0741. P0421 (Warm-...

Audi A6 | P0421

01 Eclipse GT P0421 - Warm-Up Catalyst Efficiency Below Threshold (Bank 1) Diagnosis and Repair Guidance

I'm experiencing fault code P0421 on my 2001 Eclipse GT, which indicates 'Warm-up Catalyst Efficiency Below Threshold (Bank 1)' as reported by my PocketScan Plus. The code has b...

01 eclipse GT | P0421