What is code P0420 on Peugeot 207?

The P0420 error code, “Catalyst System Efficiency Below Threshold Bank 1,” is a common diagnostic trouble code (DTC) indicating that the Powertrain Control Module (PCM) has detected that the catalytic converter on Bank 1 is not functioning as efficiently as it should. Bank 1 refers to the catalytic converter located on the engine’s side of the engine. This code doesn't necessarily mean the catalytic converter is *failed*, but rather that its performance is below the manufacturer’s specified thresholds. The Peugeot 207, particularly models from 2006 to 2015, is known to be susceptible to this code due to a combination of factors including the design of the exhaust system and the relatively aggressive engine tuning. The PCM constantly monitors the oxygen sensors (O2 sensors) before and after the catalytic converter. When the readings from these sensors are significantly different, the PCM interprets this as a problem with the catalytic converter's ability to reduce harmful emissions. The P0420 Peugeot 207 code is frequently triggered by a variety of issues, making it a complex diagnostic challenge. The catalytic converter’s primary role is to convert harmful pollutants like hydrocarbons, carbon monoxide, and nitrogen oxides into less harmful substances. It achieves this through chemical reactions facilitated by heat and a catalyst material. The O2 sensors play a crucial role in monitoring the efficiency of this process. A properly functioning catalytic converter will maintain a relatively stable voltage differential between the upstream and downstream O2 sensors. When this differential is too large, indicating reduced catalytic activity, the PCM sets the P0420 code. On the 207, the exhaust system design can sometimes lead to uneven exhaust flow, contributing to inconsistent O2 sensor readings and, ultimately, the P0420 code.

Symptoms of P0420 on Peugeot 207

  • Dashboard Check Engine Light (MIL) illuminated: This is the primary indicator.
  • Slightly Reduced Engine Power: You might notice a minor decrease in acceleration, particularly during uphill climbs or when carrying a heavy load.
  • Rough Idling: The engine may idle unevenly or feel slightly shaky.
  • Increased Exhaust Smell: While not always present, a more noticeable smell of exhaust fumes may be present, indicating incomplete combustion.
  • Poor Fuel Economy: You may observe a decrease in your vehicle’s fuel efficiency.
  • Hesitation During Acceleration: The engine might hesitate or stumble slightly when you press the accelerator pedal.
  • Slightly Higher Engine Temperatures: In some cases, the engine temperature gauge may rise slightly.
  • Catalytic Converter Warm to the Touch: Carefully feel the catalytic converter (when the exhaust system is cool!) – it should be warm, not excessively hot.

Causes of P0420 on Peugeot 207 — by frequency

  • Faulty Oxygen Sensors (O2 Sensors): The upstream (before the converter) and downstream (after the converter) O2 sensors are the most common culprits. Specifically, the DS3/207 style Bosch LSU 4.9 O2 sensors (12897507798) are known to fail prematurely.
  • Exhaust Leaks: Leaks in the exhaust system, particularly before the catalytic converter, can introduce air and affect O2 sensor readings.
  • Failing Catalytic Converter: While not always the immediate cause, a deteriorating catalytic converter can trigger the code.
  • Engine Oil Contamination: Oil leaking into the combustion chamber can contaminate the catalytic converter, reducing its efficiency.
  • Faulty Fuel Injectors: Leaky or clogged fuel injectors can cause incomplete combustion and affect the catalytic converter's performance.
  • PCM Software Issues: In rare cases, a software glitch in the PCM can cause a false P0420 code.
  • Wiring Issues: Damaged or corroded wiring to the O2 sensors can lead to inaccurate readings.
  • Loose Connections: Loose connections at the O2 sensor connectors.
  • Peugeot 207 Specific Issue: The 207’s exhaust manifold design is prone to cracking, leading to exhaust leaks and impacting O2 sensor readings.

Warning

Driving with a P0420 code for an extended period can damage the catalytic converter further, leading to more expensive repairs. Additionally, continuous emissions violations may result in failed emissions tests.

Step-by-step diagnostic procedure

  1. Scan Tool Connection: Connect a scan tool to the OBD2 port and retrieve the P0420 code. Record any other related codes.
  2. Visual Inspection: Inspect the exhaust system for leaks, particularly around the exhaust manifold and catalytic converter.
  3. O2 Sensor Check: Visually inspect the O2 sensor wiring for damage or corrosion. Check the connectors for looseness.
  4. Upstream O2 Sensor Voltage Check: With the engine running, use the scan tool to monitor the voltage output of the upstream O2 sensor. It should fluctuate rapidly between approximately 0.1V and 0.9V. A sluggish or flat voltage indicates a potential O2 sensor issue.
  5. Downstream O2 Sensor Voltage Check: Monitor the voltage output of the downstream O2 sensor. It should be relatively stable, typically around 0.45V to 0.8V. A fluctuating or high voltage indicates a problem with the catalytic converter.
  6. O2 Sensor Response Time Test: Some scan tools allow you to test the response time of the O2 sensors. Compare the response times of the upstream and downstream sensors. A significant difference can indicate a failing catalytic converter.
  7. Exhaust Backpressure Test: Using a backpressure gauge, check for excessive backpressure in the exhaust system. High backpressure indicates a clogged catalytic converter.
  8. Wiring Resistance Test: Use a multimeter to check the resistance of the O2 sensor wiring. High resistance indicates a wiring problem.
  9. Catalytic Converter Temperature Check: Use an infrared thermometer to measure the temperature of the catalytic converter. The upstream sensor side should be hotter than the downstream sensor side.

Mechanic Tip

A common mistake is to immediately replace the catalytic converter without investigating the O2 sensors. Often, a faulty O2 sensor is the root cause of the P0420 code. Replacing O2 sensors before tackling the catalytic converter can save time and money.

Repair solutions and costs for Peugeot 207

Repair DIY Cost (EUR/USD) Garage Cost (EUR/USD) Difficulty Time
Replace Upstream O2 Sensor 50-100 100-200 Medium 1-2 hours
Replace Downstream O2 Sensor 60-120 120-250 Medium 1-2 hours
Exhaust Leak Repair 30-80 80-200 Medium 1-3 hours
Catalytic Converter Replacement (OEM) 500-800 800-1500 Hard 3-6 hours
Catalytic Converter Replacement (Aftermarket) 300-600 500-1000 Medium 2-4 hours
PCM Software Update (if applicable) 0-100 100-300 Easy 30-60 minutes
Fuel Injector Cleaning/Replacement 80-200 200-400 Medium 1-3 hours

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 vehicle may still run and operate, the reduced catalytic converter efficiency can lead to increased emissions and potential failure of the catalytic converter. Prolonged exposure to high emissions can also negatively impact the environment. It's crucial to address the underlying cause of the code to prevent further damage and ensure compliance with emissions regulations. Driving with the check engine light on for more than a few days can also trigger a failed emissions test.

Frequently Asked Questions