- Air fuel ratio (A/F) sensor 1 Bank 1
- Air fuel ratio (A/F) sensor 1 heater Bank 1
- Fuel pressure
- Fuel injector
- Intake air leaks
- Air Flow Meter

There is an Infiniti service bulletin with information on how to repair the P1284 code. The bulletin is for the following models:

2003-2006 FX
2002 G20
2003-2006 G35 Sedan
2003-2006 G35 Coupe
2002-2004 I35
2004-2006 M
2002-2006 Q45
2002-2003 QX4
2004-2006 QX56

P1284 Infiniti Service Bulletin

The A/F signal computed by ECM from the A/F sensor 1 signal is shifted to the rich side for a specified period.

- Engine Light ON (or Service Engine Soon Warning Light)
- Possible rough engine idle

The A/F sensor is a planar dual-cell limit current sensor. The sensor element of the A/F sensor is the combination of a Nernst concentration cell (sensor cell) with an oxygen-pump cell, which transports ions. It has a heater in the element.

The sensor is capable of precise measurement λ= 1, but also in the lean and rich range. Together with its control electronics, the sensor outputs a clear, continuous signal throughout a wide λ range (0.7 < λ < air).

The exhaust gas components diffuse through the diffusion gap at the electrode of the oxygen pump and Nernst concentration cell, where they are brought to thermodynamic balance.

An electronic circuit controls the pump current through the oxygen-pump cell so that the composition of the exhaust gas in the diffusion gap remains constant at λ = 1. Therefore, the A/F sensor is able to indicate air/fuel ratio by this pumping of current. In addition, a heater is integrated in the sensor to ensure the required operating temperature of 700 - 800 C (1,292 - 1,472 F).