P1273 is a common Nissan diagnostic code. It indicates that the air fuel ratio sensor has detected a lean shift in the exhaust output.
An air/fuel ratio sensor is effectively an oxygen sensor with a wider band than a traditional O2 sensor. A good scan tool can really aid in this diagnosis.
P1273: Air Fuel Ratio Sensor (Sensor 1 Bank 1) – Lean Shift Monitoring
Symptoms
Here are the most common symptoms of P1273:
- Check Engine Light– If code P1273 is accompanied by any other codes (particularly oxygen sensor ones) it can really help narrow down the problem.
- Rough/Choppy Idle– As the fuel system adjusts the air fuel ratio, it can cause the vehicle to idle rough.
P1273 Causes
This code is triggered when the O2 sensor has reported a lean condition for an extended period of time.
Vacuum Leak
A good place to start your diagnosis is with the vacuum system. A vacuum leak can and will throw P1273. Here’s a pretty thorough article on finding vacuum leak from popular mechanics.
If you happen to have access to a code scanner, you can check the short term fuel trim on bank 1 and see if it changes if you squirt starting fluid at the intake manifold. The short term trim should go down if a vacuum leak is responsible for the code.
A/F Sensors
If the a/f sensors are bad, P1273 is likely to be triggered. You can do a quick inspection and see if there is any wiring issue around the upstream (before catalytic converter) or downstream (after the catalytic converter). A good code scanner will tell you if the O2 sensors have voltage or not. You can also use a volt meter.
Exhaust Leak
The exhaust system is one of the most common reasons that you’ll get this code. An exhaust gasket that has gone bad can alter the content of the oxygen in the exhaust. This will cause the A/F sensor to falsely report to the PCM that the vehicle is running lean.
Once you find the cause of the problem, you’ll need to clear the learned fuel values. Otherwise, the code will come back.
This video is a great tool that can help you diagnose the code with a scanner. Clearing the learned fuel values happens at about the 5 minute mark. It involves unplugging the MAF sensor and clearing the codes.
Conclusion
Diagnosing P1273 can be a real challenge if you don’t have a scanner. You can look for obvious problems such as frayed wiring to the a/f sensor, or an exhaust leak. Good luck!