• Car Reviews
• Test Drives
  
• Expert Opinions
• ОТЗЫВЫ ВЛАДЕЛЬЦЕВ
  
• Real-World Experience

🚦 Symptoms of Error Code P0420

Common signs you might see:

• Check Engine Light (CEL) stays on
• Drop in fuel efficiency
• Slight loss of power, especially under acceleration
• Rotten egg smell (sulfur) from the exhaust
• Failed emissions or smog test
• Occasional rough idle or hesitation (if O2 sensors also fail)

🔧 What Causes P0420 on Changan UNI-T?

Several factors may lead to this error:

Cause Description 

• Faulty catalytic converter The internal honeycomb gets clogged, cracked, or poisoned by unburned fuel, oil, or coolant.
• Worn oxygen sensors Inaccurate readings from upstream or downstream O2 sensors cause the ECM to misjudge converter efficiency.
• Exhaust leaks Even a small leak before the catalytic converter can cause the downstream sensor to detect incorrect O2 levels.
• Oil burning or misfires Can cause the cat to overheat or fail prematurely.
• ECM software issue Occasionally, incorrect ECM mapping causes false P0420 codes (rare, but possible).

🛠️ How to Fix P0420: Step-by-Step Guide

1. Scan the Code

Use an OBD-II scanner to confirm the P0420 code and check for any related codes, especially:

• P0171 / P0172 – fuel trim issues
• P0300 – misfires
• P2195 / P2197 – O2 sensor stuck readings

Clear the codes and observe if P0420 returns. 

2. Check for Exhaust Leaks

Leaks between the engine and catalytic converter may introduce extra air, which leads to incorrect O2 sensor readings.

What to do:

• Look for soot marks around the manifold or flex pipe
• Listen for hissing sounds
• Use a smoke machine or soap solution to detect leaks
• Repair with welding or replace damaged gaskets/pipes
• 
  

3. Test Oxygen Sensors

📊 Live Data Method:

Use an OBD-II scanner to view O2 sensor waveforms:

• Upstream sensor: Should fluctuate rapidly (rich/lean)
• Downstream sensor: Should be stable if the catalytic converter is working

If the downstream sensor mimics the upstream one (rapid fluctuations), the catalytic converter may be failing.

🧪 Multimeter Test:

• Test sensor resistance and heater circuit (if accessible)
• Typical resistance: 5–10 ohms (refer to service manual)
• 🛠️ Replace any faulty O2 sensors with OEM-quality parts. Cheap sensors often cause more problems.

4. Inspect or Replace the Catalytic Converter

If the sensors and exhaust system check out, it’s time to evaluate the converter itself.

Signs of a bad cat: 

• Metallic rattling when tapping on it
• Overheating under the floorboard
• Visual melting or discoloration
• Failed emissions even after clearing codes

✅ Best solution: OEM catalytic converter 💡 Budget option: Aftermarket converters — choose those with OBD2 compliance and legal emissions certification in your region.


5. ECM Reflash or Software Update

In some cases, the ECM might trigger false P0420 codes due to outdated firmware. Dealers may offer an ECM update that recalibrates the catalytic efficiency thresholds.

Ask your local Changan dealership if there’s a Technical Service Bulletin (TSB) for your UNI-T’s model year.

🧪 Optional: Use Catalytic Converter Cleaner

Sometimes carbon buildup affects the readings. You can try:

• Fuel additives that clean the converter (e.g., Cataclean)
• High-RPM highway driving (“Italian tune-up”) to burn off carbon
• Ensure the engine is fully warmed before daily short trips

🛑 This is a temporary fix — it may help delay the issue, but not solve it if the converter is truly failing.


🏷️ Estimated Repair Costs

Repair Estimated Cost (USD)

Diagnostic scan (OBD2)                     $20–$50
Oxygen sensor (each)                        $50–$120
Catalytic converter (OEM)                  $300–$800+
Catalytic converter (aftermarket)      $200–$500
Exhaust leak repair                             $50–$200
ECM reprogramming                          $100–$200

🛡️ How to Prevent P0420 in the Future

To extend the life of your catalytic converter and avoid future check engine lights:

✅ Tips:

• Use high-quality fuel and engine oil
• Stick to regular oil change intervals
• Fix engine misfires quickly
• Avoid driving with a rich fuel mixture (watch fuel trims)
• Never ignore low coolant levels or white smoke (head gasket failure)
• Use OEM-grade spark plugs and O2 sensors
• Don’t drive long-term with the CEL on, especially for misfire-related codes

❓ Frequently Asked Questions (FAQ)

Can I drive with P0420?
Yes, but prolonged driving with a faulty catalytic converter or misfiring engine can lead to further damage or failure to pass emissions.

Can I remove the catalytic converter?
In many countries (including the US, UK, EU, and parts of Asia), removing the cat is illegal and may lead to fines or failed inspections. Always check local laws.

Will P0420 cause damage if ignored?
Yes — unburned fuel can damage the catalytic converter further, affect other sensors, and reduce fuel economy. It’s best to fix it early.

Can a fuel additive fix P0420?
Sometimes. If the cat is just dirty, additives might temporarily help. But if it's physically damaged or clogged, replacement is the only solution.


✅ Final Thoughts

If your Changan UNI-T is showing a P0420 code, don’t panic. Start with a proper scan and diagnostics:

• Check for exhaust leaks
• Test or replace O2 sensors
• Inspect the catalytic converter
• Consider ECM updates if necessary

Taking action early can save you hundreds of dollars and keep your UNI-T running efficiently.