Q: Check engine light on. Code read as p0420. Bank 1 below threshold for predetermined amount of time. What 02 sensor up or lower?

asked by on

Check engine light is on. Car is slower to accelerate above 40-50. Got code read as P0420, bank 1 system was below threshold for predetermined amount of time. Car has 110,000 miles. No major issues thus far. Recently replaced serpentine belt.

Sources so far have suggested 02 sensor repair. In your services, I see upper and lower as an option. How do I know which one to choose?

Does 02 sensor make sense for that code? I would like to schedule a repair, I just don't want to waste a ton of money on useless repairs. Thank you very much.
My car has an automatic transmission.

Hi there. When the oxygen sensors have readings that are similar to each other, it is an indication that the catalytic converter is not working as intended. If the voltage of the downstream oxygen sensor decreases, and begins to fluctuate like the upstream oxygen sensor, it means that the oxygen levels are too high and the Powertrain Control Module (PCM) will store the P0420 trouble code. By having a professional mechanic complete a check engine light inspection, they can narrow the root cause of this error code - which is not always due to the O2 sensors.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. Check engine light on. Code read as p0420. Bank 1 below threshold for predetermined amount of time. What 02 sensor up or lower?

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: My Lincoln MKZ Rear Left Lid Tail Light Tail Lamp , the brake light is out I need the part number to order

Hi Donald. Thanks for the question. Unfortunately, we typically don't look up parts by VIN number to supply you with a part number, as this is something that needs to be done by a dealership. I've forwarded your inquiry to...

Q: Speedometer stick and jumps

Hello. Your Geo utilizes a speedometer cable (rather than an electronic sensor and wiring) to communicate speed from the transmission to the speedometer cluster. Given your mileage, the cable lining has probably deteriorated and the cable should be replaced. If...

Q: car jerks/gas pedal

Hi, thanks for writing in. This is more than likely a fuel delivery issue, given the symptoms you describe. The idle air control valve is a unit that regulates the air flow into the engine as it is mixed with...

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.