# P2A00 CEL Issues



## NormPhillips (Mar 17, 2015)

Hello,

On Sunday, I saw my check engine light was on my 2011 Nissan Altima 2.5s. I took it into Auto Zone and they found only one code reading: P2A00. I double checked online and spoke with friends, et cetera and they told me basically my Air Fuel Ratio (A/F) (upstream) Bank 1 Sensor 1 probably went bad. 

I took it into the shop today and have performing some inspections and tests, they told me that BOTH my upstream and downstream sensors went bad.

Does this sound feasible to you? Could they both have gone bad at the same time and yet the check engine light comes on for just the upstream sensor? Or was I just taken advantage of?

Please let me know. Thanks.


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## rogoman (Dec 16, 2004)

Check the harness connectors at the sensor. Clear the ECU code with a scan tool, then see if the code comes back.

If the code comes back, check for the following possible causes:
• A/F sensor 1.
• A/F sensor 1 heater.
• Fuel pressure. 
• Fuel injector(s) may be dirty. Run some good injection cleaner, like Techron or Redline SL-1, through the system; give the cleaner about a week or two to do it's job. 
• Intake air leaks. To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg.

If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.

Consider taking the car to another shop for a second opinion.


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## smj999smj (Jan 1, 2006)

To what did they base this rear sensor failure on? Rear sensors have no affect on engine performance and are only used as monitoring sensors to help the ECM determine catalytic converter efficiency. If there was no rear sensor code nor code for catalyst efficiency, I'd be hard pressed to believe the rear sensor was bad unless the shop can provide some other information to prove it.


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