What is code P0420 on Peugeot 208?

The P0420 diagnostic trouble code (DTC) signifies “Catalyst System Efficiency Below Threshold Bank 1.” This code indicates that the Powertrain Control Module (PCM) has detected that the catalytic converter on Bank 1 of your Peugeot 208 is not functioning as efficiently as it should. Bank 1 refers to the side of the engine where cylinder number one is located. The PCM monitors the oxygen sensors (O2 sensors) before and after the catalytic converter. When the downstream O2 sensor reading is consistently lower than the upstream sensor reading, it suggests the catalytic converter isn’t effectively reducing harmful emissions. This is a common code, and the P0420 Peugeot 208 is particularly susceptible due to certain design characteristics and common failure points in the exhaust system. The Peugeot 208, especially those manufactured between 2012 and 2016, can experience issues with exhaust leaks and deteriorated catalytic converters, leading to this code. The catalytic converter’s primary role is to convert harmful pollutants like hydrocarbons, carbon monoxide, and nitrogen oxides into less harmful substances. It does this through a chemical process involving precious metals like platinum and palladium. A failing catalytic converter will allow these pollutants to pass through, triggering the P0420 code. It’s important to note that a P0420 code doesn’t always mean the catalytic converter is completely failed; it can also be triggered by issues with the O2 sensors themselves, exhaust leaks, or other engine problems affecting oxygen levels. Accurate diagnosis is crucial to avoid unnecessary replacement of a perfectly functional catalytic converter.

Symptoms of P0420 on Peugeot 208

  • Dashboard Check Engine Light (CEL) illuminated: This is the most common symptom.
  • Reduced Engine Power: You may notice a slight decrease in acceleration or overall engine performance.
  • Rough Idling: The engine might idle unevenly or vibrate noticeably.
  • Increased Exhaust Smoke: While not always present, a slight increase in dark or grey exhaust smoke, particularly during acceleration, can be a sign of incomplete combustion.
  • Fuel Economy Decrease: The Peugeot 208’s fuel efficiency may decline as the engine struggles to burn fuel effectively.
  • Slight Metallic Smell: In severe cases of catalytic converter failure, a faint metallic smell emanating from the exhaust could be present.
  • Hesitation During Acceleration: A noticeable hesitation or stumble when accelerating, particularly from a stop.
  • Failed Emissions Test: The vehicle may fail an emissions test due to elevated levels of pollutants.

Causes of P0420 on Peugeot 208 — by frequency

  • Faulty Oxygen Sensors (Upstream & Downstream): The O2 sensors are the most common cause of a P0420 code on the Peugeot 208. The upstream sensor provides data to the PCM, and the downstream sensor monitors the catalytic converter’s performance.
    Warning: A failing O2 sensor can mimic a failing catalytic converter, leading to unnecessary replacement. Always verify O2 sensor functionality before replacing the catalytic converter.
  • Exhaust Leaks: Leaks in the exhaust system, particularly around the catalytic converter or upstream joints, can introduce air into the exhaust stream, skewing O2 sensor readings and triggering the code.
  • Worn or Deteriorated Catalytic Converter: Over time, catalytic converters can become clogged or damaged, reducing their efficiency. The Peugeot 208, particularly those with higher mileage, are known to experience catalytic converter degradation.
  • Engine Issues: Problems like oil leaks into the combustion chamber, rich fuel mixtures, or misfires can damage the catalytic converter.
  • PCM Software Issues: In rare cases, a software glitch in the PCM can trigger a false P0420 code.
  • Contaminated Catalytic Converter: Excessive use of fuel additives or exposure to corrosive substances can damage the catalytic converter.
  • Loose or Corroded Connectors: Corrosion or loose connections to the O2 sensors or the catalytic converter can cause intermittent readings.
  • Mechanic Tip: Inspect all exhaust connections for signs of leaks – soot, rust, or discoloration. Use a smoke machine to pinpoint leaks accurately.

Step-by-step diagnostic procedure

  1. Scan for Codes: Use an OBD2 scanner to confirm the presence of P0420 and any other related codes.
  2. Inspect O2 Sensors: Visually inspect the upstream and downstream O2 sensors for damage or corrosion. Check the wiring and connectors for looseness or damage.
  3. Check for Exhaust Leaks: Perform a visual inspection of the exhaust system, paying close attention to the catalytic converter and exhaust manifold. Use a smoke machine to identify any leaks.
  4. Test O2 Sensor Readings: Using a multimeter, check the voltage output of the O2 sensors. Compare the readings to manufacturer specifications. The upstream sensor should fluctuate rapidly, while the downstream sensor should be relatively stable.
  5. Inspect Catalytic Converter: Visually inspect the catalytic converter for damage, excessive heat shielding, or signs of deterioration.
  6. Check Wiring and Connectors: Ensure that all wiring and connectors to the O2 sensors and catalytic converter are clean, secure, and free of corrosion.
  7. Perform a Fuel Trim Analysis: Use an OBD2 scanner to check the short-term and long-term fuel trims. High fuel trims can indicate an engine problem affecting the catalytic converter.
  8. Check for Misfires: Scan for misfire codes (P0300-P0304) as misfires can damage the catalytic converter.

Repair solutions and costs for Peugeot 208

Repair DIY Cost (EUR/USD) Garage Cost (EUR/USD) Difficulty Time
Oxygen Sensor Replacement (Upstream) 50-150 150-300 Medium 1-2 hours
Oxygen Sensor Replacement (Downstream) 60-180 200-400 Medium 1-2 hours
Exhaust Leak Repair (Minor) 30-80 100-250 Easy 30-60 minutes
Catalytic Converter Replacement 400-800 600-1200 Medium-Hard 2-4 hours
Catalytic Converter Cleaning (if applicable) 100-300 200-500 Easy 30-60 minutes
PCM Software Update (if applicable) 0-200 150-400 Medium 1-2 hours
O2 Sensor Wiring Repair 20-50 80-150 Easy 30-60 minutes

Can I drive with code P0420?

Driving with a P0420 code is generally permissible for short distances, but it’s not recommended for extended periods. While the engine might still run, the reduced efficiency of the catalytic converter can lead to increased emissions and potentially damage the engine over time. Prolonged driving with a faulty catalytic converter can also result in further emissions failures and potential fines. It’s crucial to address the underlying cause of the code as soon as possible to prevent more serious issues and ensure compliance with environmental regulations. Driving for more than 50-100 kilometers with a persistent P0420 is discouraged.

Frequently Asked Questions

Question: What is the typical repair cost for a P0420 code on a Peugeot 208?

Answer: The cost can vary significantly depending on the cause. Replacing an O2 sensor typically costs between €50 and €300. A minor exhaust leak repair could be around €30-€80. However, catalytic converter replacement is the most expensive, ranging from €400 to €1200, depending on the brand and quality.

Question: How long can I drive with a P0420 code?

Answer: It's best not to drive for extended periods. For short trips (under 50km), it’s usually okay, but for anything longer, you should have it diagnosed and repaired to avoid further damage to the engine and potential emissions violations.

Question: Is it possible to DIY a P0420 repair on a Peugeot 208?

Answer: Replacing O2 sensors and fixing minor