im trying to do a test on one of my o2 sensors to see if they need replaced or if theyre getting enough voltage. the way I'm testing it is getting 0.0 volts to the electrical connector. but since I'm an absolute newb at electrical and doing any types of tests with it, I'm more inclined to think I'm doing the test wrong. so heres a step by step of what I'm doing to test it. tell me which step(s) I'm doing wrong if any. I'm working on a 96 4.9l. on the sensor closest to the front of the truck (easiest to reach)

1. let the truck idle until reaches normal operating temp
2. turn off engine but leave ignition on
3. unplug o2 sensor connector
4. take multimeter and set it to 20v dc.
5. put black lead on negative terminal of battery
6. put positive lead on one of the prongs inside connector
7. not getting anything
8. try it with each of the other three prongs (theres two white wires and one black and one gray. I'm not sure which is which as my manual didn't say or at least i couldn't find where. I'm guessing that black is ground, gray is power to the sensor and the two white ones are for the sensor heater. correct me if I'm wrong)
9. still nothing.
10. make a post asking for help on f150 forum

so where am i screwing this up?

thanks in advance guys, sorry if i sound like a total newb. but i kinda am when it comes to electrical. id like to get better

 

Probe the connector with the engine running and see if you have any voltage to any of the lines. Of course having it unplugged while running will set a trouble code but that's easily erased once you're done testing.

 

ok, I did what you said and got 12 volts to two different connectors I tested. my question now is, what do I need to do to get the signal I should be getting from the o2 sensor (oscillating between 0.1v and 0.9 or 1v) how do I do that test to know if ive got a bad o2 sensor??

 

should've mentioned before that theyre already setting codes. that's why I'm testing them. p0135 p0141 and p0155 if I'm not mistaken.

 

When those codes are set on obd2 the o2 sensor has gone bad. The only exception would be a wiring/fuse problem. If you are getting voltage at the sensor that pretty much rules that out.

 

in that case I'm buying o2 sensors. the sensor closest to the front of the truck is the upstream sensor correct? I'm buying just one right now and waiting till I get paid to get the other one(s)