Possible causes

For Models 2005 and up:
– Faulty Air Fuel Ratio Sensor 1 Bank 1
– Air Fuel Ratio Sensor 1 Bank 1 circuit is open or shorted
– Air Fuel Ratio Sensor 1 Bank 1 circuit electrical connection

For Models before 2005:
– Faulty Heated Oxygen Sensor 1 Bank 1
– Heated Oxygen Sensor 1 Bank 1 circuit is open or shorted
– Heated Oxygen Sensor 1 Bank 1 circuit electrical connection

Tech notes

There is a factory service bulletin for the following Infiniti models:

2004-2005 Infiniti FX35
2004-2005 Infiniti FX45
2004-2005 Infiniti G35 Sedan
2004-2005 Infiniti G35 Sedan
Infiniti Factory Service Bulletin OBDII Code P1148

The bulletin suggest reprogramming the Engine Control Module (ECM) first before replacing any parts.

When is the code detected?

The closed loop control function for bank 1 does not operate even when vehicle is driving in the specified condition, the closed loop control function for bank 2 does not operate even when vehicle is driving in the specified condition.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P1148 INFINITI Description

The Engine Control Module (ECM) performs ON/OFF duty control of the Air Fuel Ratio (A/F)/Heated Oxygen Sensor 1 heater corresponding to the engine operating condition to keep the temperature of Air Fuel Ratio (A/F)/Heated Oxygen Sensor 1 element at the specified range.

INFINITI Technical Service Bulletins for P1148 code