What is code P0420 on Peugeot 5008?

The OBD2 diagnostic trouble code (DTC) P0420 indicates that the Powertrain Control Module (PCM) has detected that the efficiency of the catalytic converter on Bank 1 is below the specified threshold. Specifically, this means the oxygen sensor (O2 sensor) upstream of the catalytic converter is reporting a relatively high amount of oxygen, while the downstream O2 sensor is not showing a significant reduction in oxygen levels after the catalytic converter has done its job. This discrepancy suggests that the catalytic converter is not functioning as efficiently as it should, or that there’s an issue upstream affecting its performance. On the Peugeot 5008, this code is particularly common due to the engine's design and the age of the vehicles, often exacerbated by particulate filter (DPF) systems, if equipped.

The catalytic converter’s primary function is to reduce harmful emissions by converting pollutants like hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) into less harmful substances. The upstream O2 sensor monitors the oxygen content in the exhaust stream before it enters the catalytic converter, providing feedback to the PCM to adjust the air-fuel mixture. The downstream O2 sensor monitors the oxygen content *after* the catalytic converter has operated, confirming the converter’s effectiveness. The P0420 Peugeot 5008 code arises when the PCM sees a large difference between these two readings, indicating a problem with the catalytic converter’s ability to perform its function. Incorrect fuel trims and aging components are frequent contributors to this issue on this model.

Diagnosing P0420 on a Peugeot 5008 requires a systematic approach, considering potential issues ranging from simple sensor faults to more complex catalytic converter problems. Understanding the specific engine configuration (e.g., diesel vs. petrol) and any installed emissions control systems (like DPFs) is crucial for accurate diagnosis and repair. The Peugeot 5008, particularly models from 2009, can be susceptible to issues related to the exhaust system and oxygen sensors if not properly maintained.

Symptoms of P0420 on Peugeot 5008

  • Dashboard Check Engine Light illuminated – Persistent or intermittent flashing.
  • Slightly reduced engine power – Noticeable during acceleration, particularly uphill.
  • Increased fuel consumption – The car may use more fuel than normal.
  • Slightly rough idling – The engine may vibrate or idle unevenly.
  • Exhaust fumes – A faint smell of unburnt fuel might be noticeable, especially during cold starts.
  • Hesitation during acceleration – The engine might lag momentarily before responding to the accelerator pedal.
  • Reduced throttle response – The car may feel sluggish when accelerating.
  • Increased noise from the exhaust system – Though less common, a rattling or hissing sound could indicate exhaust leaks contributing to the issue.

Causes of P0420 on Peugeot 5008 — by frequency

  • Faulty Oxygen Sensors (Upstream or Downstream): 35% – Degradation or contamination of the O2 sensors is a common cause.
  • Catalytic Converter Failure: 25% – The catalytic converter itself may be clogged or damaged, reducing its efficiency.
  • Exhaust Leaks: 15% – Leaks upstream of the catalytic converter can introduce extra oxygen, triggering the code.
  • Fuel Trim Issues: 10% – Incorrect fuel mixture due to sensor problems or PCM calibration can affect catalytic converter performance.
  • Particulate Filter (DPF) Issues (if equipped): 10% – A clogged DPF can restrict exhaust flow and affect catalytic converter efficiency. Peugeot 5008 models with diesel engines are particularly prone to DPF problems.
  • PCM Software Issues: 5% – Rarely, a software glitch in the PCM can cause incorrect readings.

Warning

Driving with a P0420 code for an extended period can lead to further damage to the catalytic converter and potentially other engine components. While the car may still run, emissions will be elevated, and you risk violating emissions regulations. Address the issue promptly.

Mechanic Tip

A common mistake is to immediately replace the catalytic converter without investigating other potential causes. Always check O2 sensor readings and exhaust leaks first – it’s often a cheaper and more effective solution.

Step-by-step diagnostic procedure

  1. Scan for Codes: Use an OBD2 scanner to confirm the P0420 code and retrieve any related diagnostic trouble codes (DTCs).
  2. Check O2 Sensor Readings: Using a scan tool with live data capabilities, monitor the upstream and downstream O2 sensor readings. Record the values during idle and under acceleration. Expected values on a Peugeot 5008 are typically around 0.4-0.8V for the upstream sensor and 0.1-0.4V for the downstream sensor. Significant deviations indicate a sensor issue.
  3. Inspect Exhaust System: Visually inspect the entire exhaust system for leaks, particularly around the catalytic converter flanges, exhaust manifold, and downpipe. Use a soapy water solution to check for bubbles forming when the engine is running.
  4. Check Fuel Trims: Access the PCM data through a scan tool and examine the short-term and long-term fuel trim values. Excessive positive or negative fuel trims can indicate a sensor or fuel delivery problem.
  5. Test O2 Sensors: Use a multimeter to test the resistance of the O2 sensors. Compare the readings to the manufacturer’s specifications. A faulty sensor needs replacement.
  6. Check Wiring and Connectors: Inspect the wiring and connectors for the O2 sensors and catalytic converter for damage, corrosion, or loose connections.
  7. Catalytic Converter Temperature Test: Using an infrared thermometer, measure the temperature of the catalytic converter inlet and outlet. A significant temperature difference (typically 30-50°C) indicates proper function. Low outlet temperature suggests a converter issue.
  8. Component Replacement (if needed): Based on the diagnostic findings, replace faulty components such as O2 sensors, catalytic converter, or exhaust gaskets. Use genuine Peugeot parts or equivalent quality replacements.

Mechanic Tip

When replacing O2 sensors on a Peugeot 5008, ensure you use the correct sensor type (e.g., Bosch LSU 4.9) and torque specifications to avoid damaging the sensor or the vehicle’s electrical system.

Repair solutions and costs for Peugeot 5008

Repair DIY Cost (EUR) Garage Cost (EUR) Difficulty Time
Oxygen Sensor Replacement (Upstream) 80 - 150 120 - 250 Medium 1-2 hours
Oxygen Sensor Replacement (Downstream) 70 - 140 110 - 230 Medium 1-2 hours
Catalytic Converter Replacement 300 - 800 500 - 1200 Hard 3-6 hours
Exhaust Leak Repair (Gasket Replacement) 50 - 150 100 - 200 Easy 30-60 minutes
Fuel Injector Cleaning/Replacement 60 - 200 150 - 400 Medium 1-3 hours
PCM Software Update (if applicable) 0 - 100 100 - 300 Easy 30-60 minutes
DPF Cleaning (if equipped) 80 - 200 150 - 350 Medium 1-2 hours

Can I drive with code P0420?

Driving with a P0420 code is generally not recommended for extended periods. While the Peugeot 5008 might still run, the reduced catalytic converter efficiency will result in increased emissions, potentially violating environmental regulations