Mazda MX-5 P2272:  B2S2 O2 Sensor – Stuck Lean

P2272 Mazda MX-5

P2272 in the Mazda MX-5 is a general diagnostic trouble code.  It means that the “bank 2” downstream oxygen sensor (behind the catalytic converter) is continuously sending voltage that indicates a lean air/fuel mixture.  

This does not necessarily mean that the vehicle is running lean (although it can, but usually doesn’t).  P2272 is typically caused by a bad oxygen sensor, or an exhaust leak.


Bank 2 Sensor 2 Location

There are oxygen sensors on both sides of your MX-5’s catalytic converter(s).  This lets it read the exhaust before and after it runs through each converter to make sure that it is removing pollutants.  

Here’s what P2272 means, and how to find Bank 2 Sensor 2.

P2272: O2 Sensor Signal → Biased/Stuck Lean (Bank 2 | Sensor 2)

  • Bank 2 is the side of your MX-5’s engine with the second cylinder.  If it has a four cylinder engine, you don’t have to worry about this, as there is only one cylinder head.  If you do have more than one cylinder head (as is the case here), you will need to look up where cylinder one is for your particular engine.  Correspondingly, P2270 affects bank 1.
  • Sensor 2 is “downstream” of the catalytic converter, which means that it is the sensor that comes after the catalytic converter.  On some vehicles, there may be a second sensor (B2S3) after the catalytic converter, but if that were causing the problem, you’d be dealing with P2276.

P2272 Symptoms:  Mazda MX-5

Mazda MX-5 P2272 Check Engine

There are almost never any symptoms associated with P2272.  It is indicating that the signal coming from the oxygen sensor at B2S2 is leaner than it should be.  

The signal from the oxygen sensor upstream of the catalytic converter does not agree with the lean condition indicated by the downstream oxygen sensor.  If it did, you’d have P0171.

There are usually no drivability issues when P2272 appears by itself.

P2272 Causes:  Mazda MX-5

Here are some of the more common causes of P2272.

Exhaust Leak (Highly Likely)

An exhaust leak is one of the more common reasons why P2272 is thrown.  If an exhaust leak is big enough to cause P2272, it’s probably going to be big enough to make some noticeable noise.

Oxygen Sensor (Highly Likely)

P2272 Causes
Your O2 sensor will be under the car after the catalytic converter.

If there isn’t an exhaust leak, the most likely cause of P2272 is a bad O2 sensor.  Take a look at the wiring going to it and see if it looks cracked or corroded. The O2 sensor wiring harnesses (due to their proximity to the exhaust system) have some of the roughest lives of any automotive wiring.

You can check your MX-5’s wiring harness with a multimeter set to OHMS.  Check the resistance compared to the factory specs.  Or if you have dual exhaust, check it vs the other downstream O2 sensor.

You can also check the voltage at the oxygen sensor if you have a good scan tool.  It should fluctuate as you press the gas.  If it’s stuck at 0, that would indicate that the sensor itself is bad.

Other Causes

  • Low fuel pressure
  • Loose O2 sensor
  • Bad fuel injector on bank 2
  • Bad purge valve
  • Bad PCM 

Conclusion:  P2272 is Usually Caused by a Bad O2 Sensor

It’s normally the oxygen sensor that needs replaced when P2272 appears.  But, there can be other issues as well.  Good luck fixing your MX-5!

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