P1273

A/F Sensor 1 Lean Shift Monitoring (Bank 1)

Car Fault Codes Nissan Emissions & exhaust

Can you still drive? Yes, normally

Who can fix it? Needs a workshop

Typical repair time 30 minutes – 2 hours

Typical cost SAR 150 to 1,500

What it means

This is a Nissan-specific code; the same number can mean something different on other makes. It means the engine computer found that the signal from the front air/fuel ratio sensor (sensor 1, before the catalytic converter) on bank 1 is consistently shifted toward lean. The cause may be the sensor itself, or a truly lean mixture from an air leak or weak fuel delivery.

Models covered: Nissan models with air/fuel ratio sensors, mainly around 2003–2008.

Symptoms4

Check engine light on.
Slight hesitation or weakness on acceleration in some cases.
A slightly rough idle if the mixture is actually lean.
Driving may feel normal if only the sensor has drifted.

Possible causes6

An aged or contaminated front air/fuel ratio sensor.
An air leak in the intake, vacuum hoses or PCV system.
An exhaust leak ahead of the sensor that lets in outside air.
Low fuel pressure or dirty injectors.
Inaccurate readings from the mass airflow (MAF) sensor.
A fault in the sensor heater or its wiring.

How to diagnose6

Read all codes; P0171 alongside this code points to a truly lean mixture rather than a sensor-only fault.
Watch short- and long-term fuel trims on a scan tool; high positive values confirm too little fuel or too much air.
Check for air leaks with a smoke test or by listening for hissing around the intake manifold.
Check the exhaust ahead of the sensor for leaks.
Measure fuel pressure against the manufacturer specification and review the MAF reading.
If all checks pass, the sensor itself has most likely drifted.

How to fix6

Fix any air leak in the vacuum hoses, intake or PCV system.
Repair the exhaust leak ahead of the sensor.
Clean the MAF sensor with a dedicated cleaner.
Correct low fuel pressure or dirty injectors if confirmed.
Replace the bank 1 front air/fuel ratio sensor if it is confirmed to have drifted.
Clear the codes and drive until the self-test completes, then confirm the code does not return.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is low when an air leak or MAF cleaning is the fix, and rises if a new air/fuel ratio sensor or fuel system repair is needed.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

Is the sensor always the faulty part?

No. The code means the signal is shifted lean, which may be correct if the mixture really is lean from an air leak or weak fuel delivery, so check those causes before replacing the sensor.

How is this sensor different from a regular O2 sensor?

An air/fuel ratio sensor measures the mixture precisely over a wide range, while a regular O2 sensor only signals rich or lean. The correct type for the car must be fitted.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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