Question

2007 Infiniti M35 5.0L with engine codes P1148 and P1421, what to do when the codes come up on the scanner?

Answer 1

You mean 3.5 L engine.

The P1148 codes mean that you probably have a faulty Air Fuel Ratio Sensor 1 Bank 1

Read more: P1148 INFINITI - Closed Loop Control Function Bank 1

The sensor is located under the vehicle on the passenger side before the catalytic converter.