Questions about O2 sensors....plus.....

[mikecgolf]

96 328i Conv. 95K miles, manual trans.


Getting the code that precat 4,5,6 cylds O2 sensor is not pre heating.

Can you tell me:

1. where the fuse and or relay for the O2 preheat is located?

2. does each O2 sensor (4 of them) have a seperate fuse and or relay?

Are these sensors easily located, reached, and removed? do you need a special socket?

Thanks!!!!

[Manolito]

The oxygen sensor heaters get power from the red/white wire that is the common power source to all kinds of different things in the engine control system. If the problem were the relay, lots of things from the mass airflow sensor to the vapor purge would not be working.

Either the oxygen sensor is bad, or the wire to that sensor is damaged. At 95k miles, you are just about to have to replace all four sensors anyway. The owner's manual says to change them every 90k miles, and my experience is that they don't go much farther than that.

I would get all four sensors and look carefully at the wires upstream from their plugs while I was replacing them. NTK sensors (OEM) are $100 each.

All you need to replace the sensors is a combination wrench and a set of ramps. Do them one at a time so you don't cross the wires. Soak them in penetrating oil overnight before you try to loosen them. Sometimes they are pretty well frozen in place. The new sensors should come with antisieze compound already on the threads.

[mikecgolf]

So there is no other fuse associated with this pre heat function?

I am thinking that the sensors are starting to go.

Thanks again.

MC