P1646 and P1647 on your XJ

P1646 and P1647 are two mighty and very common Oxygen sensor codes. The first (P1646 is for the right bank, here in the USA that's the passenger side) and the other (P1647 is for the left bank or driver's side in the USA). The probable causes are:

1. Oxygen sensor failure: fixes the problem 95% of the time
2. Oxygen sensor circuit failure (either the connector or the cable going to the computer): Fixes the problem 1% of the time 
3. Computer failure: fixes the problem 4% of the time

The computer is constantly comparing the upstream Oxygen sensors with the downstream oxygen sensors so it is always recommended to change them in pairs (front and rear for each bank). All you have to do to fix your code is to replace both oxygen sensors respective to your bank. For a guide on which parts to buy look below:

Question: What oxygen sensors do I need?

Answer: Depends on what car... Buy one of each, here is a guide:

1997 - 1998 XJ8 with a 3.2L and a 4.0L engine

• NGK 25620 for the front
• NGK 25573 for the rear

1999 - 2003 XJ8 with a 3.2L and a 4.0L engine

• Denso 234-9016 for the front
• Denso 234-4798 for the rear

2003 - 2005 XJ with a 4.2L engine

• Denso 234-9030 for the front
• Denso 234-4798 for the rear

2006 - 2009 XJ with a 4.2L engine

• Denso 234-9125 for the front
• Bosch 15373 for the rear