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2016 V60 T5 - P0420 Code, Reduced MPG, Sulfur Smell

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Mike T. · rep 0 · May 25, 3:53 AM · 1 replies · solved · Question

Vehicle: 2016 Volvo V60 T5

Hey forum,

I've got a 2016 Volvo V60 T5 with about 95,000 miles, and I'm running into an issue that's causing me some concern. The check engine light came on about a week ago, and when I scanned it, I got a P0420 code, which points to 'Catalyst System Efficiency Below Threshold (Bank 1)'.

Along with the CEL, I've noticed a significant drop in my fuel economy lately, and there's a distinct sulfur or rotten egg smell coming from the exhaust, especially after driving for a bit. The car otherwise seems to be running fine, no noticeable power loss or rough idle, but the smell and MPG are definitely off.

Is this a common problem for the 2016 V60 T5? Could it just be an O2 sensor, or am I looking at a catalytic converter replacement? Any advice on how to confirm the diagnosis or what steps I should take next?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 3:53 AM

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ClearTheCode admin answer:

The P0420 code, combined with reduced fuel economy and a sulfur smell, strongly suggests an issue with your catalytic converter's efficiency. While an O2 sensor can sometimes trigger this code, the smell and MPG drop make a failing catalytic converter more likely.

Here's a breakdown of what's likely happening and what to do:

  1. Catalytic Converter Failure: The sulfur smell (rotten eggs) is a classic symptom of a catalytic converter that is no longer efficiently converting hydrogen sulfide into odorless sulfur dioxide. The P0420 code means the post-catalytic converter oxygen sensor is detecting similar oxygen levels to the pre-catalytic converter sensor, indicating the catalyst isn't doing its job.
  2. Oxygen Sensors: While less likely to cause the sulfur smell, a faulty downstream (post-cat) O2 sensor could falsely report low efficiency. However, a failing catalytic converter often causes the O2 sensor to read out of spec, rather than the sensor being the primary issue.
  3. Engine Running Rich: Sometimes, an underlying engine issue causing the engine to run excessively rich (too much fuel) can overload and damage the catalytic converter over time. This could be due to faulty fuel injectors, a leaking fuel pressure regulator, or even a persistent misfire (though you mentioned no power loss).

When to See a Shop:

  • Soon: While a P0420 code doesn't typically require immediate roadside assistance, it's important to address it promptly. A failing catalytic converter can significantly increase harmful emissions and, if left unaddressed, could eventually become clogged, leading to severe exhaust restriction, loss of power, and even engine damage.
  • A qualified Volvo technician can perform a thorough diagnosis. This usually involves:
    • Checking O2 Sensor Readings: Using a diagnostic scanner to monitor live data from both upstream and downstream O2 sensors to see if they are switching correctly and if the catalyst is showing proper efficiency.
    • Visual Inspection: Looking for exhaust leaks before or around the catalytic converter.
    • Backpressure Test: Measuring exhaust backpressure to see if the converter is internally clogged.
    • They can accurately determine if it's the O2 sensor, an underlying engine issue, or indeed a failing catalytic converter that needs replacement.
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