What Does the Engine Code P2A04 Mean?

If your car is showing the P2A04 engine code, your vehicle has a problem with its rear oxygen sensor.
Written by Marlee John
Reviewed by Melanie Reiff
If your vehicle is displaying the P2A04 engine code, your oxygen sensor is either damaged or not functioning correctly. This code doesn’t indicate a direct danger for the driver, however, you should get it fixed quickly to avoid other problems with your vehicle including significantly reduced fuel efficiency.
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What does the engine code P2A04 mean?

Definition: O2 sensor Circuit Range/Performance Bank 2 Sensor 2 
The P2A04 engine code is signaling an issue with your vehicle’s rear oxygen sensor, a sensor responsible for reading the oxygen levels in the air coming out of your car’s exhaust pipe.

How much will it cost to fix? 

Oftentimes, you will need to replace the
oxygen sensor
, which comes at an additional cost of $20 to $200 for the part. While
car repair costs
vary by location, an approximate total cost to replace could be anywhere from $75 to $150 per hour
Diagnosis time and repair rates may change based on factors such as the mechanic’s location, the make of your vehicle, and your engine type.
MORE: How to know if a mechanic is taking too long with car repairs

What can cause the P2A04 engine code? 

If your vehicle is displaying the P2A04 engine code, it’s likely because the rear oxygen sensors aren’t working properly. The malfunction may be the result of the following: the sensor harness is open or shorted, the circuit has a bad electrical connection, or the sensor itself is simply faulty and in need of replacement. 
Rear oxygen sensors are small sensors that reside at the back end of your car’s exhaust system. These sensors are responsible for evaluating the quality of air that leaves the exhaust pipe, which can be used to determine the efficiency of your vehicle. 
Some other possible causes for this code include: 
  • Incorrect fuel pressure (too high or too low)
  • Intake air leaks may be malfunctioning
  • Exhaust gas leaks 

Common symptoms of the P2A04 engine code 

Some common symptoms of the P2A04 engine code include: 
  • Check Engine Light is ON
    (or the Service Engine Soon warning light) 
  • Bad gas mileage
  • Excessive smoke from the exhaust pipe

How serious is the P2A04 engine code? 

Your car may start and be drivable with a P2A04 engine code, but it will quickly accumulate other problems if you wait too long before getting it fixed. 
The oxygen (or O2) sensor is responsible for helping your vehicle adjust its air-fuel levels. Without the sensor, your fuel efficiency will suffer, and your car’s emissions will be unregulated. It may also cause your vehicle to stall. 
If your car is showing the P2A04 engine code, you should get it fixed (by a professional) immediately

Can I fix the P2A04 engine code myself?

While experienced car owners with access to the needed parts may be able to do it at home, it’s much safer to leave it to a professional who has the proper tools and training to diagnose and repair it. 
You can visually inspect it to see if any wires or connectors look out of place or damaged, but you want to ensure that the job is done properly before you get back on the road. After all, this is your safety at risk!  
In most cases, replacing the rear O2 sensor bank 2 solves the issue. 

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