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2017 Tacoma TRD Off-Road - P0420 Code and Reduced MPG

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

Vehicle: 2017 Toyota Tacoma TRD Off-Road

Hey Tacoma owners,

I've got a 2017 Toyota Tacoma TRD Off-Road with the 3.5L V6, just hit 85,000 miles. A few weeks ago, my check engine light came on, and when I scanned it, I got a P0420 code: 'Catalyst System Efficiency Below Threshold (Bank 1)'.

Since then, I've noticed a slight drop in my fuel economy, maybe 1-2 MPG, and occasionally the exhaust smells a bit richer than usual. The truck still runs fine, no misfires or obvious power loss, but the CEL is annoying, and I'm worried about the catalytic converter.

Has anyone dealt with this P0420 code on their Tacoma? What was the fix? I've heard it could be O2 sensors, an exhaust leak, or the cat itself. Any advice on how to troubleshoot this before I commit to potentially expensive repairs?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 1:25 AM

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ClearTheCode admin answer:

The P0420 code on your 2017 Toyota Tacoma TRD Off-Road indicates that the catalytic converter on Bank 1 is not operating efficiently enough to reduce emissions as required. While it often points to a failing catalytic converter, it's crucial to rule out other, less expensive causes first.

Possible Causes:

  1. Failing Catalytic Converter: Over time, catalytic converters can become clogged or their internal substrate can degrade, losing efficiency. This is the most common reason for a P0420 code.
  2. Faulty Oxygen Sensors (O2 Sensors): Specifically, the downstream (post-catalyst) O2 sensor monitors the catalyst's efficiency. If this sensor is faulty, it might incorrectly report low efficiency. The upstream (pre-catalyst) O2 sensor also plays a role in fuel mixture, and if it's inaccurate, it can cause the catalyst to work harder.
  3. Exhaust Leaks: Leaks in the exhaust system before or between the O2 sensors can allow unmetered air in, skewing O2 sensor readings and leading the ECU to believe the catalyst is inefficient.
  4. Engine Misfires or Rich/Lean Conditions: Persistent misfires, fuel injector issues, or other engine problems causing an improper air/fuel mixture can damage the catalytic converter over time or trigger the code due to excessive unburnt fuel reaching the cat.

When to See a Shop:

  • Soon: While the truck runs fine now, a failing catalytic converter can eventually restrict exhaust flow, leading to significant power loss and further fuel economy degradation. It also means your truck is producing higher emissions.
  • If you experience: Rough idling, significant power loss, or a very strong rotten egg smell (sulfur) from the exhaust.

What to Expect:

  1. Comprehensive Diagnostic Scan: A professional scan tool can monitor live data from both upstream and downstream O2 sensors to compare their readings and determine if the catalyst is truly inefficient or if a sensor is faulty.
  2. Exhaust System Inspection: The mechanic will check for any exhaust leaks, especially around the manifold, pipes, and O2 sensor bungs.
  3. Engine Performance Check: They will verify that the engine is running properly, checking for misfires, proper fuel pressure, and injector function.
  4. Catalytic Converter Test: In some cases, a backpressure test can be performed to check for a clogged catalytic converter. If all other components are ruled out, replacement of the catalytic converter may be necessary. Ensure you get an OEM or high-quality aftermarket unit for proper function and longevity.
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