I have found three of the 4 or more O2 sensors and from reading old posts I think this code refers to the engineward (flow-wise) of the two on the manifold between the (below the front windshield) firewall and the block (rear of the block facing engine from front of car).

Is this correct?

Then P0051 then refers to the upper sensor on the oposite bank...

What codes refer to the other sensors and how many more are their... for instance does code P0031 refer only to that upper O2 sensor and some other code refers to the lower...

Thanks.

 

Also, is there any trick to disconnecting the harness plug connector? I was having trouble getting the lower one disconnected without being able to see it when I started pulling it by mistake... before finding the upper one.

 

Those codes indicate o2 sensor heater failure. You can test the heaters with an ohm meter. The 2 black wires are for the preheater circuit. Unplug them and ohm them outfirst. 6 ohms or so is good. They get power from the black/white wire.

 

What does the plug connector look like ? I dont want to break it but could be 100,000 miles has just made it resistant to removal...hard to say when you can't see anything back there. Is there something to depress or pry up on the connector?

 

You can follow the o2 sensor to find the connector. There is a little red slide tab that locks it then just push the other tab and pull.

 

Ah a slide tab. That expains it. Thanks.