...between the three wires guys?

 

For a good sensor I mean :cool:

Hope this helps

 

Warm the car up, and with the car at hot idle and with the connectors all plugged in, insert an open safety pin into the end of the connector along the red wire, making sure that it makes contact with the red wire inside the connector. Connect the voltmeter (low volts range, eg 20 V) with red probe to the safety pin and black to earth. You should see 12 volts DC. Note the engine should be above 2,000rpm while performing the test.

 

Then plug the safety pin into the white wire, making sure that it makes contact with the white wire inside the connector. Connect the voltmeter (low volts range, eg 2 volts) with red probe to the safety pin and black to earth. A good 02 sensor when warm should show the voltage moving between around 0.3 volts DC and around 0.7 volts DC - this is the ECU cycling the oxygen content (via varying the fuel content) to keep the ratio correct. At higher revs, the upper voltage increases from memory, but it always cycles, except possibly at WOT (which I recommend that you DON'T do while parked in the driveway! ).

 

If the voltage reading doesn't cycle, then it's probable that the 02 sensor or cable/connector is stuffed. I'm not sure about the Zed, but some/most 02 sensors take a while to heat up, so until the engine and exhaust are hot enough, the ecu usually operates in 'open loop', which means that the voltage won't vary. Thus, you have to do the test when the engine is hot, eg after a 10 minute drive.

 

The Black/red wire is a heating wire I think - most 02 sensors have a heating coil in them to help them heat up. NOTE! I've seen a Zed 02 sensor test article on a web page somewhere which says to check the resistance between the red/black wire and the black wire - this is only testing the heater coil, not the actual 02 sensor, so it's not a valid test.

 

Lastly, the Zed ecu controls the 02 sensors via the black wires to each sensor. THEY DO NOT GO STARIGHT TO EARTH. Don't use the black wires for the above test - use a chassis earth, or the battery negative.

 

Cheers

Graham

That's GREAT advice Graham - much appreciated. WIll test later and feed back.

 

What would happen if the Red and Blue were switched - it looks like I have after market O2 sensors with 2 x white and one black connector sir!!!!

 

Andy

Red and blue? usually red, black and a white, Probably not aftermarket, may be discoloured from the heat. You are looking at getting a cycle reading akin to an led sound bar up and down with the beat of the music.

 

The best way to be sure is to get it on a consult diagnostic, you can actually see the sensors working............. or not

 

Cheers

Graham

Thanks again Graham