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PO420 and still confused

OK...I just put my scope away and I'm as confused as I was before. I'll make it simple. Here are my questions...

  1. We have 4 O2 sensors, right? 2 upstream and 2 downstream?...bank 1 and bank 2.

  1. Should both upstreams be cycling between .1 and .9V or just one of them?

  2. Where is bank 1 and where is bank 2?

  1. Bonus point here: There are 4 connectors at the front of the motor, the three left go to O2 sensors. What is what?....for example left connector to bank 2 upstream. Middle connector to bank 2 downstream, and right connector to downstream on bank 1. There's another connector for the 4th O2 sensor on top of the passenger's side fender well. Is that upstream?...downstream....bank 1 ...bank 2...?

Here's what I've got: front L connector cycles from .1 to .9. Middle connector stays at .4 with no change even with a lean or rich condition. The others will change with lean or rich condition.

lastly, only the one o2 sensor cycles it's voltage up and down.

Thanks in advance.

Reply to
unix-freak
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What year Maxima and are you from Cali?

Only the California emissions Maxima's have 4 o2 sensors. The rest have 3, two in the y-pipe, and one on (95-96) or after (97-99) the cat.

Nick

Reply to
Nick

It's a 2001 SE and I'm on the east coast.

Reply to
unix-freak

Ah ok, then you do have 4 sensors.

Nick

Reply to
Nick

I guess the thing that confusing me, is that with 2 upstream sensors, I would expect both to be cycling instead of one just sitting at .4v.

Reply to
unix-freak

What are you using to measure the volts? I don't think you can just use your average multimeter on O2 sensors, you'll throw the impedance completely off and get goofy results.

JM

Reply to
JM

Your absolutely right. An analog volt ohmmeter that's rated at

20Kohms/V will load down the circuit and give false readings.

I'm using a dual channel Tektronix oscilloscope for monitoring upstream/downstream simultaneously. There's obviously no loading issues there.

Reply to
unix-freak

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