The largest online repair guide library for every car

About us
Contact support
FAQ
Sign up
Sign in

2018 Discovery Sport P0420 Code - Check Engine Light On

0

Mike T. · rep 0 · May 24, 3:43 PM · 1 replies · solved · Question

Vehicle: 2018 Land Rover Discovery Sport HSE

Hey everyone,

My 2018 Land Rover Discovery Sport HSE recently threw a Check Engine Light, and when I scanned it, I got a P0420 code: 'Catalyst System Efficiency Below Threshold (Bank 1)'. The car seems to be driving mostly fine, but I feel like my fuel economy might have dipped slightly, and there's a subtle exhaust smell sometimes.

I'm wondering what the most common culprits are for this code on a Discovery Sport of this vintage. Is it usually an O2 sensor, or am I looking at a potentially more expensive catalytic converter replacement? I'd appreciate any advice on troubleshooting steps I can take myself before heading to the dealer.

Thanks for your help!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 24, 3:43 PM

0

ClearTheCode admin answer:

The P0420 code on your 2018 Land Rover Discovery Sport indicates that the catalytic converter on Bank 1 is not operating at optimal efficiency. While it points to the catalytic converter, it doesn't always mean the converter itself is bad. Here's a breakdown of common causes and diagnostic steps:

  1. Oxygen Sensors: Failing upstream or downstream oxygen sensors can trigger a P0420. The downstream O2 sensor monitors the catalytic converter's efficiency. If it's faulty, it might incorrectly report low efficiency.
  2. Exhaust Leaks: Any leaks in the exhaust system before or near the catalytic converter can introduce unmetered air, confusing the O2 sensors and leading to a P0420.
  3. Catalytic Converter Failure: Over time, catalytic converters can become clogged or damaged, reducing their ability to convert harmful emissions. This is often due to engine misfires, excessive oil consumption, or fuel additives.
  4. Engine Misfires: Consistent misfires can send unburnt fuel into the catalytic converter, causing it to overheat and fail prematurely.

Troubleshooting Steps:

  1. Check for Exhaust Leaks: Visually inspect the exhaust system for any cracks, holes, or loose connections, especially around the manifold and catalytic converter.
  2. Monitor O2 Sensor Data: If you have a capable scan tool, monitor the live data for both upstream and downstream O2 sensors on Bank 1. A healthy downstream sensor should show a relatively steady voltage, while a failing converter might cause it to mimic the upstream sensor's fluctuations.
  3. Fuel System Inspection: Ensure your fuel system is operating correctly, as rich or lean conditions can impact converter life.

When to See a Shop:

If after checking for exhaust leaks and monitoring O2 sensor data you're still unsure, or if the code persists, it's best to consult a qualified Land Rover specialist. They have advanced diagnostic tools to perform a comprehensive analysis, including backpressure tests on the catalytic converter and more detailed O2 sensor diagnostics, to accurately pinpoint the root cause and recommend the correct repair.

Menu

Help & account